core/intrinsics/

mod.rs

//! Compiler intrinsics.
//!
//! The functions in this module are implementation details of `core` and should
//! not be used outside of the standard library. We generally provide access to
//! intrinsics via stable wrapper functions. Use these instead.
//!
//! These are the imports making intrinsics available to Rust code. The actual implementations live in the compiler.
//! Some of these intrinsics are lowered to MIR in <https://github.com/rust-lang/rust/blob/HEAD/compiler/rustc_mir_transform/src/lower_intrinsics.rs>.
//! The remaining intrinsics are implemented for the LLVM backend in <https://github.com/rust-lang/rust/blob/HEAD/compiler/rustc_codegen_ssa/src/mir/intrinsic.rs>
//! and <https://github.com/rust-lang/rust/blob/HEAD/compiler/rustc_codegen_llvm/src/intrinsic.rs>,
//! and for const evaluation in <https://github.com/rust-lang/rust/blob/HEAD/compiler/rustc_const_eval/src/interpret/intrinsics.rs>.
//!
//! # Const intrinsics
//!
//! In order to make an intrinsic unstable usable at compile-time, copy the implementation from
//! <https://github.com/rust-lang/miri/blob/master/src/intrinsics> to
//! <https://github.com/rust-lang/rust/blob/HEAD/compiler/rustc_const_eval/src/interpret/intrinsics.rs>
//! and make the intrinsic declaration below a `const fn`. This should be done in coordination with
//! wg-const-eval.
//!
//! If an intrinsic is supposed to be used from a `const fn` with a `rustc_const_stable` attribute,
//! `#[rustc_intrinsic_const_stable_indirect]` needs to be added to the intrinsic. Such a change requires
//! T-lang approval, because it may bake a feature into the language that cannot be replicated in
//! user code without compiler support.
//!
//! # Volatiles
//!
//! The volatile intrinsics provide operations intended to act on I/O
//! memory, which are guaranteed to not be reordered by the compiler
//! across other volatile intrinsics. See [`read_volatile`][ptr::read_volatile]
//! and [`write_volatile`][ptr::write_volatile].
//!
//! # Atomics
//!
//! The atomic intrinsics provide common atomic operations on machine
//! words, with multiple possible memory orderings. See the
//! [atomic types][atomic] docs for details.
//!
//! # Unwinding
//!
//! Rust intrinsics may, in general, unwind. If an intrinsic can never unwind, add the
//! `#[rustc_nounwind]` attribute so that the compiler can make use of this fact.
//!
//! However, even for intrinsics that may unwind, rustc assumes that a Rust intrinsics will never
//! initiate a foreign (non-Rust) unwind, and thus for panic=abort we can always assume that these
//! intrinsics cannot unwind.

#![unstable(
    feature = "core_intrinsics",
    reason = "intrinsics are unlikely to ever be stabilized, instead \
                      they should be used through stabilized interfaces \
                      in the rest of the standard library",
    issue = "none"
)]

use crate::ffi::{VaArgSafe, VaList};
use crate::marker::{ConstParamTy, DiscriminantKind, PointeeSized, Tuple};
use crate::{mem, ptr};

mod bounds;
pub mod fallback;
pub mod gpu;
pub mod mir;
pub mod simd;

// These imports are used for simplifying intra-doc links
#[allow(unused_imports)]
#[cfg(all(target_has_atomic = "8", target_has_atomic = "32", target_has_atomic = "ptr"))]
use crate::sync::atomic::{self, AtomicBool, AtomicI32, AtomicIsize, AtomicU32, Ordering};

/// A type for atomic ordering parameters for intrinsics. This is a separate type from
/// `atomic::Ordering` so that we can make it `ConstParamTy` and fix the values used here without a
/// risk of leaking that to stable code.
#[allow(missing_docs)]
#[derive(Debug, ConstParamTy, PartialEq, Eq)]
#[ferrocene::prevalidated]
pub enum AtomicOrdering {
    // These values must match the compiler's `AtomicOrdering` defined in
    // `rustc_middle/src/ty/consts/int.rs`!
    Relaxed = 0,
    Release = 1,
    Acquire = 2,
    AcqRel = 3,
    SeqCst = 4,
}

// N.B., these intrinsics take raw pointers because they mutate aliased
// memory, which is not valid for either `&` or `&mut`.

/// Stores a value if the current value is the same as the `old` value.
/// `T` must be an integer or pointer type.
///
/// The stabilized version of this intrinsic is available on the
/// [`atomic`] types via the `compare_exchange` method.
/// For example, [`AtomicBool::compare_exchange`].
#[rustc_intrinsic]
#[rustc_nounwind]
pub unsafe fn atomic_cxchg<
    T: Copy,
    const ORD_SUCC: AtomicOrdering,
    const ORD_FAIL: AtomicOrdering,
>(
    dst: *mut T,
    old: T,
    src: T,
) -> (T, bool);

/// Stores a value if the current value is the same as the `old` value.
/// `T` must be an integer or pointer type. The comparison may spuriously fail.
///
/// The stabilized version of this intrinsic is available on the
/// [`atomic`] types via the `compare_exchange_weak` method.
/// For example, [`AtomicBool::compare_exchange_weak`].
#[rustc_intrinsic]
#[rustc_nounwind]
pub unsafe fn atomic_cxchgweak<
    T: Copy,
    const ORD_SUCC: AtomicOrdering,
    const ORD_FAIL: AtomicOrdering,
>(
    _dst: *mut T,
    _old: T,
    _src: T,
) -> (T, bool);

/// Loads the current value of the pointer.
/// `T` must be an integer or pointer type.
///
/// The stabilized version of this intrinsic is available on the
/// [`atomic`] types via the `load` method. For example, [`AtomicBool::load`].
#[rustc_intrinsic]
#[rustc_nounwind]
pub unsafe fn atomic_load<T: Copy, const ORD: AtomicOrdering>(src: *const T) -> T;

/// Stores the value at the specified memory location.
/// `T` must be an integer or pointer type.
///
/// The stabilized version of this intrinsic is available on the
/// [`atomic`] types via the `store` method. For example, [`AtomicBool::store`].
#[rustc_intrinsic]
#[rustc_nounwind]
pub unsafe fn atomic_store<T: Copy, const ORD: AtomicOrdering>(dst: *mut T, val: T);

/// Stores the value at the specified memory location, returning the old value.
/// `T` must be an integer or pointer type.
///
/// The stabilized version of this intrinsic is available on the
/// [`atomic`] types via the `swap` method. For example, [`AtomicBool::swap`].
#[rustc_intrinsic]
#[rustc_nounwind]
pub unsafe fn atomic_xchg<T: Copy, const ORD: AtomicOrdering>(dst: *mut T, src: T) -> T;

/// Adds to the current value, returning the previous value.
/// `T` must be an integer or pointer type.
/// `U` must be the same as `T` if that is an integer type, or `usize` if `T` is a pointer type.
///
/// The stabilized version of this intrinsic is available on the
/// [`atomic`] types via the `fetch_add` method. For example, [`AtomicIsize::fetch_add`].
#[rustc_intrinsic]
#[rustc_nounwind]
pub unsafe fn atomic_xadd<T: Copy, U: Copy, const ORD: AtomicOrdering>(dst: *mut T, src: U) -> T;

/// Subtract from the current value, returning the previous value.
/// `T` must be an integer or pointer type.
/// `U` must be the same as `T` if that is an integer type, or `usize` if `T` is a pointer type.
///
/// The stabilized version of this intrinsic is available on the
/// [`atomic`] types via the `fetch_sub` method. For example, [`AtomicIsize::fetch_sub`].
#[rustc_intrinsic]
#[rustc_nounwind]
pub unsafe fn atomic_xsub<T: Copy, U: Copy, const ORD: AtomicOrdering>(dst: *mut T, src: U) -> T;

/// Bitwise and with the current value, returning the previous value.
/// `T` must be an integer or pointer type.
/// `U` must be the same as `T` if that is an integer type, or `usize` if `T` is a pointer type.
///
/// The stabilized version of this intrinsic is available on the
/// [`atomic`] types via the `fetch_and` method. For example, [`AtomicBool::fetch_and`].
#[rustc_intrinsic]
#[rustc_nounwind]
pub unsafe fn atomic_and<T: Copy, U: Copy, const ORD: AtomicOrdering>(dst: *mut T, src: U) -> T;

/// Bitwise nand with the current value, returning the previous value.
/// `T` must be an integer or pointer type.
/// `U` must be the same as `T` if that is an integer type, or `usize` if `T` is a pointer type.
///
/// The stabilized version of this intrinsic is available on the
/// [`AtomicBool`] type via the `fetch_nand` method. For example, [`AtomicBool::fetch_nand`].
#[rustc_intrinsic]
#[rustc_nounwind]
pub unsafe fn atomic_nand<T: Copy, U: Copy, const ORD: AtomicOrdering>(dst: *mut T, src: U) -> T;

/// Bitwise or with the current value, returning the previous value.
/// `T` must be an integer or pointer type.
/// `U` must be the same as `T` if that is an integer type, or `usize` if `T` is a pointer type.
///
/// The stabilized version of this intrinsic is available on the
/// [`atomic`] types via the `fetch_or` method. For example, [`AtomicBool::fetch_or`].
#[rustc_intrinsic]
#[rustc_nounwind]
pub unsafe fn atomic_or<T: Copy, U: Copy, const ORD: AtomicOrdering>(dst: *mut T, src: U) -> T;

/// Bitwise xor with the current value, returning the previous value.
/// `T` must be an integer or pointer type.
/// `U` must be the same as `T` if that is an integer type, or `usize` if `T` is a pointer type.
///
/// The stabilized version of this intrinsic is available on the
/// [`atomic`] types via the `fetch_xor` method. For example, [`AtomicBool::fetch_xor`].
#[rustc_intrinsic]
#[rustc_nounwind]
pub unsafe fn atomic_xor<T: Copy, U: Copy, const ORD: AtomicOrdering>(dst: *mut T, src: U) -> T;

/// Maximum with the current value using a signed comparison.
/// `T` must be a signed integer type.
///
/// The stabilized version of this intrinsic is available on the
/// [`atomic`] signed integer types via the `fetch_max` method. For example, [`AtomicI32::fetch_max`].
#[rustc_intrinsic]
#[rustc_nounwind]
pub unsafe fn atomic_max<T: Copy, const ORD: AtomicOrdering>(dst: *mut T, src: T) -> T;

/// Minimum with the current value using a signed comparison.
/// `T` must be a signed integer type.
///
/// The stabilized version of this intrinsic is available on the
/// [`atomic`] signed integer types via the `fetch_min` method. For example, [`AtomicI32::fetch_min`].
#[rustc_intrinsic]
#[rustc_nounwind]
pub unsafe fn atomic_min<T: Copy, const ORD: AtomicOrdering>(dst: *mut T, src: T) -> T;

/// Minimum with the current value using an unsigned comparison.
/// `T` must be an unsigned integer type.
///
/// The stabilized version of this intrinsic is available on the
/// [`atomic`] unsigned integer types via the `fetch_min` method. For example, [`AtomicU32::fetch_min`].
#[rustc_intrinsic]
#[rustc_nounwind]
pub unsafe fn atomic_umin<T: Copy, const ORD: AtomicOrdering>(dst: *mut T, src: T) -> T;

/// Maximum with the current value using an unsigned comparison.
/// `T` must be an unsigned integer type.
///
/// The stabilized version of this intrinsic is available on the
/// [`atomic`] unsigned integer types via the `fetch_max` method. For example, [`AtomicU32::fetch_max`].
#[rustc_intrinsic]
#[rustc_nounwind]
pub unsafe fn atomic_umax<T: Copy, const ORD: AtomicOrdering>(dst: *mut T, src: T) -> T;

/// An atomic fence.
///
/// The stabilized version of this intrinsic is available in
/// [`atomic::fence`].
#[rustc_intrinsic]
#[rustc_nounwind]
pub unsafe fn atomic_fence<const ORD: AtomicOrdering>();

/// An atomic fence for synchronization within a single thread.
///
/// The stabilized version of this intrinsic is available in
/// [`atomic::compiler_fence`].
#[rustc_intrinsic]
#[rustc_nounwind]
pub unsafe fn atomic_singlethreadfence<const ORD: AtomicOrdering>();

/// The `prefetch` intrinsic is a hint to the code generator to insert a prefetch instruction
/// for the given address if supported; otherwise, it is a no-op.
/// Prefetches have no effect on the behavior of the program but can change its performance
/// characteristics.
///
/// The `LOCALITY` argument is a temporal locality specifier ranging from (0) - no locality,
/// to (3) - extremely local keep in cache.
///
/// This intrinsic does not have a stable counterpart.
#[rustc_intrinsic]
#[rustc_nounwind]
#[miri::intrinsic_fallback_is_spec]
pub const fn prefetch_read_data<T, const LOCALITY: i32>(data: *const T) {
    // This operation is a no-op, unless it is overridden by the backend.
    let _ = data;
}

/// The `prefetch` intrinsic is a hint to the code generator to insert a prefetch instruction
/// for the given address if supported; otherwise, it is a no-op.
/// Prefetches have no effect on the behavior of the program but can change its performance
/// characteristics.
///
/// The `LOCALITY` argument is a temporal locality specifier ranging from (0) - no locality,
/// to (3) - extremely local keep in cache.
///
/// This intrinsic does not have a stable counterpart.
#[rustc_intrinsic]
#[rustc_nounwind]
#[miri::intrinsic_fallback_is_spec]
pub const fn prefetch_write_data<T, const LOCALITY: i32>(data: *const T) {
    // This operation is a no-op, unless it is overridden by the backend.
    let _ = data;
}

/// The `prefetch` intrinsic is a hint to the code generator to insert a prefetch instruction
/// for the given address if supported; otherwise, it is a no-op.
/// Prefetches have no effect on the behavior of the program but can change its performance
/// characteristics.
///
/// The `LOCALITY` argument is a temporal locality specifier ranging from (0) - no locality,
/// to (3) - extremely local keep in cache.
///
/// This intrinsic does not have a stable counterpart.
#[rustc_intrinsic]
#[rustc_nounwind]
#[miri::intrinsic_fallback_is_spec]
pub const fn prefetch_read_instruction<T, const LOCALITY: i32>(data: *const T) {
    // This operation is a no-op, unless it is overridden by the backend.
    let _ = data;
}

/// The `prefetch` intrinsic is a hint to the code generator to insert a prefetch instruction
/// for the given address if supported; otherwise, it is a no-op.
/// Prefetches have no effect on the behavior of the program but can change its performance
/// characteristics.
///
/// The `LOCALITY` argument is a temporal locality specifier ranging from (0) - no locality,
/// to (3) - extremely local keep in cache.
///
/// This intrinsic does not have a stable counterpart.
#[rustc_intrinsic]
#[rustc_nounwind]
#[miri::intrinsic_fallback_is_spec]
pub const fn prefetch_write_instruction<T, const LOCALITY: i32>(data: *const T) {
    // This operation is a no-op, unless it is overridden by the backend.
    let _ = data;
}

/// Executes a breakpoint trap, for inspection by a debugger.
///
/// This intrinsic does not have a stable counterpart.
#[rustc_intrinsic]
#[rustc_nounwind]
pub fn breakpoint();

/// Magic intrinsic that derives its meaning from attributes
/// attached to the function.
///
/// For example, dataflow uses this to inject static assertions so
/// that `rustc_peek(potentially_uninitialized)` would actually
/// double-check that dataflow did indeed compute that it is
/// uninitialized at that point in the control flow.
///
/// This intrinsic should not be used outside of the compiler.
#[rustc_nounwind]
#[rustc_intrinsic]
pub fn rustc_peek<T>(_: T) -> T;

/// Aborts the execution of the process.
///
/// Note that, unlike most intrinsics, this is safe to call;
/// it does not require an `unsafe` block.
/// Therefore, implementations must not require the user to uphold
/// any safety invariants.
///
/// [`std::process::abort`](../../std/process/fn.abort.html) is to be preferred if possible,
/// as its behavior is more user-friendly and more stable.
///
/// The current implementation of `intrinsics::abort` is to invoke an invalid instruction,
/// on most platforms.
/// On Unix, the
/// process will probably terminate with a signal like `SIGABRT`, `SIGILL`, `SIGTRAP`, `SIGSEGV` or
/// `SIGBUS`.  The precise behavior is not guaranteed and not stable.
///
/// The stabilization-track version of this intrinsic is [`core::process::abort_immediate`].
#[rustc_nounwind]
#[rustc_intrinsic]
pub fn abort() -> !;

/// Informs the optimizer that this point in the code is not reachable,
/// enabling further optimizations.
///
/// N.B., this is very different from the `unreachable!()` macro: Unlike the
/// macro, which panics when it is executed, it is *undefined behavior* to
/// reach code marked with this function.
///
/// The stabilized version of this intrinsic is [`core::hint::unreachable_unchecked`].
#[rustc_intrinsic_const_stable_indirect]
#[rustc_nounwind]
#[rustc_intrinsic]
pub const unsafe fn unreachable() -> !;

/// Informs the optimizer that a condition is always true.
/// If the condition is false, the behavior is undefined.
///
/// No code is generated for this intrinsic, but the optimizer will try
/// to preserve it (and its condition) between passes, which may interfere
/// with optimization of surrounding code and reduce performance. It should
/// not be used if the invariant can be discovered by the optimizer on its
/// own, or if it does not enable any significant optimizations.
///
/// The stabilized version of this intrinsic is [`core::hint::assert_unchecked`].
#[rustc_intrinsic_const_stable_indirect]
#[rustc_nounwind]
#[unstable(feature = "core_intrinsics", issue = "none")]
#[rustc_intrinsic]
#[ferrocene::annotation(
    "Cannot be covered, since the purpose of the function is to never receive a `b` that is `false`, and if it does it will kill the process."
)]
#[ferrocene::prevalidated]
pub const unsafe fn assume(b: bool) {
    if !b {
        // SAFETY: the caller must guarantee the argument is never `false`
        unsafe { unreachable() }
    }
}

/// Hints to the compiler that current code path is cold.
///
/// Note that, unlike most intrinsics, this is safe to call;
/// it does not require an `unsafe` block.
/// Therefore, implementations must not require the user to uphold
/// any safety invariants.
///
/// The stabilized version of this intrinsic is [`core::hint::cold_path`].
#[ferrocene::annotation(
    "All calls of this function are removed during code generation as this is only a hint used to do certain optimizations. The correctness of the code generation is tested in `tests/codegen-llvm/intrinsics/cold_path.rs`, `tests/codegen-llvm/intrinsics/cold_path2.rs` and `tests/codegen-llvm/intrinsics/cold_path3.rs`."
)]
#[rustc_intrinsic]
#[rustc_nounwind]
#[miri::intrinsic_fallback_is_spec]
#[cold]
#[ferrocene::prevalidated]
pub const fn cold_path() {}

/// Hints to the compiler that branch condition is likely to be true.
/// Returns the value passed to it.
///
/// Any use other than with `if` statements will probably not have an effect.
///
/// Note that, unlike most intrinsics, this is safe to call;
/// it does not require an `unsafe` block.
/// Therefore, implementations must not require the user to uphold
/// any safety invariants.
///
/// This intrinsic does not have a stable counterpart.
#[unstable(feature = "core_intrinsics", issue = "none")]
#[rustc_nounwind]
#[inline(always)]
#[ferrocene::prevalidated]
pub const fn likely(b: bool) -> bool {
    if b {
        true
    } else {
        cold_path();
        false
    }
}

/// Hints to the compiler that branch condition is likely to be false.
/// Returns the value passed to it.
///
/// Any use other than with `if` statements will probably not have an effect.
///
/// Note that, unlike most intrinsics, this is safe to call;
/// it does not require an `unsafe` block.
/// Therefore, implementations must not require the user to uphold
/// any safety invariants.
///
/// This intrinsic does not have a stable counterpart.
#[unstable(feature = "core_intrinsics", issue = "none")]
#[rustc_nounwind]
#[inline(always)]
#[ferrocene::prevalidated]
pub const fn unlikely(b: bool) -> bool {
    if b {
        cold_path();
        true
    } else {
        false
    }
}

/// Returns either `true_val` or `false_val` depending on condition `b` with a
/// hint to the compiler that this condition is unlikely to be correctly
/// predicted by a CPU's branch predictor (e.g. a binary search).
///
/// This is otherwise functionally equivalent to `if b { true_val } else { false_val }`.
///
/// Note that, unlike most intrinsics, this is safe to call;
/// it does not require an `unsafe` block.
/// Therefore, implementations must not require the user to uphold
/// any safety invariants.
///
/// The public form of this intrinsic is [`core::hint::select_unpredictable`].
/// However unlike the public form, the intrinsic will not drop the value that
/// is not selected.
#[ferrocene::annotation(
    "All calls of this function are replaced during code generation, meaning that the code inside the function is never run. The correctness of the code generation is tested in `tests/codegen-llvm/intrinsics/select_unpredictable.rs`"
)]
#[unstable(feature = "core_intrinsics", issue = "none")]
#[rustc_const_unstable(feature = "const_select_unpredictable", issue = "145938")]
#[rustc_intrinsic]
#[rustc_nounwind]
#[miri::intrinsic_fallback_is_spec]
#[inline]
#[ferrocene::prevalidated]
pub const fn select_unpredictable<T>(b: bool, true_val: T, false_val: T) -> T {
    if b {
        forget(false_val);
        true_val
    } else {
        forget(true_val);
        false_val
    }
}

/// A guard for unsafe functions that cannot ever be executed if `T` is uninhabited:
/// This will statically either panic, or do nothing. It does not *guarantee* to ever panic,
/// and should only be called if an assertion failure will imply language UB in the following code.
///
/// This intrinsic does not have a stable counterpart.
#[rustc_intrinsic_const_stable_indirect]
#[rustc_nounwind]
#[rustc_intrinsic]
pub const fn assert_inhabited<T>();

/// A guard for unsafe functions that cannot ever be executed if `T` does not permit
/// zero-initialization: This will statically either panic, or do nothing. It does not *guarantee*
/// to ever panic, and should only be called if an assertion failure will imply language UB in the
/// following code.
///
/// This intrinsic does not have a stable counterpart.
#[rustc_intrinsic_const_stable_indirect]
#[rustc_nounwind]
#[rustc_intrinsic]
pub const fn assert_zero_valid<T>();

/// A guard for `std::mem::uninitialized`. This will statically either panic, or do nothing. It does
/// not *guarantee* to ever panic, and should only be called if an assertion failure will imply
/// language UB in the following code.
///
/// This intrinsic does not have a stable counterpart.
#[rustc_intrinsic_const_stable_indirect]
#[rustc_nounwind]
#[rustc_intrinsic]
pub const fn assert_mem_uninitialized_valid<T>();

/// Gets a reference to a static `Location` indicating where it was called.
///
/// Note that, unlike most intrinsics, this is safe to call;
/// it does not require an `unsafe` block.
/// Therefore, implementations must not require the user to uphold
/// any safety invariants.
///
/// Consider using [`core::panic::Location::caller`] instead.
#[rustc_intrinsic_const_stable_indirect]
#[rustc_nounwind]
#[rustc_intrinsic]
pub const fn caller_location() -> &'static crate::panic::Location<'static>;

/// Moves a value out of scope without running drop glue.
///
/// This exists solely for [`crate::mem::forget_unsized`]; normal `forget` uses
/// `ManuallyDrop` instead.
///
/// Note that, unlike most intrinsics, this is safe to call;
/// it does not require an `unsafe` block.
/// Therefore, implementations must not require the user to uphold
/// any safety invariants.
#[rustc_intrinsic_const_stable_indirect]
#[rustc_nounwind]
#[rustc_intrinsic]
pub const fn forget<T: ?Sized>(_: T);

/// Reinterprets the bits of a value of one type as another type.
///
/// Both types must have the same size. Compilation will fail if this is not guaranteed.
///
/// `transmute` is semantically equivalent to a bitwise move of one type
/// into another. It copies the bits from the source value into the
/// destination value, then forgets the original. Note that source and destination
/// are passed by-value, which means if `Src` or `Dst` contain padding, that padding
/// is *not* guaranteed to be preserved by `transmute`.
///
/// Both the argument and the result must be [valid](../../nomicon/what-unsafe-does.html) at
/// their given type. Violating this condition leads to [undefined behavior][ub]. The compiler
/// will generate code *assuming that you, the programmer, ensure that there will never be
/// undefined behavior*. It is therefore your responsibility to guarantee that every value
/// passed to `transmute` is valid at both types `Src` and `Dst`. Failing to uphold this condition
/// may lead to unexpected and unstable compilation results. This makes `transmute` **incredibly
/// unsafe**. `transmute` should be the absolute last resort.
///
/// Because `transmute` is a by-value operation, alignment of the *transmuted values
/// themselves* is not a concern. As with any other function, the compiler already ensures
/// both `Src` and `Dst` are properly aligned. However, when transmuting values that *point
/// elsewhere* (such as pointers, references, boxes…), the caller has to ensure proper
/// alignment of the pointed-to values.
///
/// The [nomicon](../../nomicon/transmutes.html) has additional documentation.
///
/// [ub]: ../../reference/behavior-considered-undefined.html
///
/// # Transmutation between pointers and integers
///
/// Special care has to be taken when transmuting between pointers and integers, e.g.
/// transmuting between `*const ()` and `usize`.
///
/// Transmuting *pointers to integers* in a `const` context is [undefined behavior][ub], unless
/// the pointer was originally created *from* an integer. (That includes this function
/// specifically, integer-to-pointer casts, and helpers like [`dangling`][crate::ptr::dangling],
/// but also semantically-equivalent conversions such as punning through `repr(C)` union
/// fields.) Any attempt to use the resulting value for integer operations will abort
/// const-evaluation. (And even outside `const`, such transmutation is touching on many
/// unspecified aspects of the Rust memory model and should be avoided. See below for
/// alternatives.)
///
/// Transmuting *integers to pointers* is a largely unspecified operation. It is likely *not*
/// equivalent to an `as` cast. Doing non-zero-sized memory accesses with a pointer constructed
/// this way is currently considered undefined behavior.
///
/// All this also applies when the integer is nested inside an array, tuple, struct, or enum.
/// However, `MaybeUninit<usize>` is not considered an integer type for the purpose of this
/// section. Transmuting `*const ()` to `MaybeUninit<usize>` is fine---but then calling
/// `assume_init()` on that result is considered as completing the pointer-to-integer transmute
/// and thus runs into the issues discussed above.
///
/// In particular, doing a pointer-to-integer-to-pointer roundtrip via `transmute` is *not* a
/// lossless process. If you want to round-trip a pointer through an integer in a way that you
/// can get back the original pointer, you need to use `as` casts, or replace the integer type
/// by `MaybeUninit<$int>` (and never call `assume_init()`). If you are looking for a way to
/// store data of arbitrary type, also use `MaybeUninit<T>` (that will also handle uninitialized
/// memory due to padding). If you specifically need to store something that is "either an
/// integer or a pointer", use `*mut ()`: integers can be converted to pointers and back without
/// any loss (via `as` casts or via `transmute`).
///
/// # Examples
///
/// There are a few things that `transmute` is really useful for.
///
/// Turning a pointer into a function pointer. This is *not* portable to
/// machines where function pointers and data pointers have different sizes.
///
/// ```
/// fn foo() -> i32 {
///     0
/// }
/// // Crucially, we `as`-cast to a raw pointer before `transmute`ing to a function pointer.
/// // This avoids an integer-to-pointer `transmute`, which can be problematic.
/// // Transmuting between raw pointers and function pointers (i.e., two pointer types) is fine.
/// let pointer = foo as fn() -> i32 as *const ();
/// let function = unsafe {
///     std::mem::transmute::<*const (), fn() -> i32>(pointer)
/// };
/// assert_eq!(function(), 0);
/// ```
///
/// Extending a lifetime, or shortening an invariant lifetime. This is
/// advanced, very unsafe Rust!
///
/// ```
/// struct R<'a>(&'a i32);
/// unsafe fn extend_lifetime<'b>(r: R<'b>) -> R<'static> {
///     unsafe { std::mem::transmute::<R<'b>, R<'static>>(r) }
/// }
///
/// unsafe fn shorten_invariant_lifetime<'b, 'c>(r: &'b mut R<'static>)
///                                              -> &'b mut R<'c> {
///     unsafe { std::mem::transmute::<&'b mut R<'static>, &'b mut R<'c>>(r) }
/// }
/// ```
///
/// # Alternatives
///
/// Don't despair: many uses of `transmute` can be achieved through other means.
/// Below are common applications of `transmute` which can be replaced with safer
/// constructs.
///
/// Turning raw bytes (`[u8; SZ]`) into `u32`, `f64`, etc.:
///
/// ```
/// # #![allow(unnecessary_transmutes)]
/// let raw_bytes = [0x78, 0x56, 0x34, 0x12];
///
/// let num = unsafe {
///     std::mem::transmute::<[u8; 4], u32>(raw_bytes)
/// };
///
/// // use `u32::from_ne_bytes` instead
/// let num = u32::from_ne_bytes(raw_bytes);
/// // or use `u32::from_le_bytes` or `u32::from_be_bytes` to specify the endianness
/// let num = u32::from_le_bytes(raw_bytes);
/// assert_eq!(num, 0x12345678);
/// let num = u32::from_be_bytes(raw_bytes);
/// assert_eq!(num, 0x78563412);
/// ```
///
/// Turning a pointer into a `usize`:
///
/// ```no_run
/// let ptr = &0;
/// let ptr_num_transmute = unsafe {
///     std::mem::transmute::<&i32, usize>(ptr)
/// };
///
/// // Use an `as` cast instead
/// let ptr_num_cast = ptr as *const i32 as usize;
/// ```
///
/// Note that using `transmute` to turn a pointer to a `usize` is (as noted above) [undefined
/// behavior][ub] in `const` contexts. Also outside of consts, this operation might not behave
/// as expected -- this is touching on many unspecified aspects of the Rust memory model.
/// Depending on what the code is doing, the following alternatives are preferable to
/// pointer-to-integer transmutation:
/// - If the code just wants to store data of arbitrary type in some buffer and needs to pick a
///   type for that buffer, it can use [`MaybeUninit`][crate::mem::MaybeUninit].
/// - If the code actually wants to work on the address the pointer points to, it can use `as`
///   casts or [`ptr.addr()`][pointer::addr].
///
/// Turning a `*mut T` into a `&mut T`:
///
/// ```
/// let ptr: *mut i32 = &mut 0;
/// let ref_transmuted = unsafe {
///     std::mem::transmute::<*mut i32, &mut i32>(ptr)
/// };
///
/// // Use a reborrow instead
/// let ref_casted = unsafe { &mut *ptr };
/// ```
///
/// Turning a `&mut T` into a `&mut U`:
///
/// ```
/// let ptr = &mut 0;
/// let val_transmuted = unsafe {
///     std::mem::transmute::<&mut i32, &mut u32>(ptr)
/// };
///
/// // Now, put together `as` and reborrowing - note the chaining of `as`
/// // `as` is not transitive
/// let val_casts = unsafe { &mut *(ptr as *mut i32 as *mut u32) };
/// ```
///
/// Turning a `&str` into a `&[u8]`:
///
/// ```
/// // this is not a good way to do this.
/// let slice = unsafe { std::mem::transmute::<&str, &[u8]>("Rust") };
/// assert_eq!(slice, &[82, 117, 115, 116]);
///
/// // You could use `str::as_bytes`
/// let slice = "Rust".as_bytes();
/// assert_eq!(slice, &[82, 117, 115, 116]);
///
/// // Or, just use a byte string, if you have control over the string
/// // literal
/// assert_eq!(b"Rust", &[82, 117, 115, 116]);
/// ```
///
/// Turning a `Vec<&T>` into a `Vec<Option<&T>>`.
///
/// To transmute the inner type of the contents of a container, you must make sure to not
/// violate any of the container's invariants. For `Vec`, this means that both the size
/// *and alignment* of the inner types have to match. Other containers might rely on the
/// size of the type, alignment, or even the `TypeId`, in which case transmuting wouldn't
/// be possible at all without violating the container invariants.
///
/// ```
/// let store = [0, 1, 2, 3];
/// let v_orig = store.iter().collect::<Vec<&i32>>();
///
/// // clone the vector as we will reuse them later
/// let v_clone = v_orig.clone();
///
/// // Using transmute: this relies on the unspecified data layout of `Vec`, which is a
/// // bad idea and could cause Undefined Behavior.
/// // However, it is no-copy.
/// let v_transmuted = unsafe {
///     std::mem::transmute::<Vec<&i32>, Vec<Option<&i32>>>(v_clone)
/// };
///
/// let v_clone = v_orig.clone();
///
/// // This is the suggested, safe way.
/// // It may copy the entire vector into a new one though, but also may not.
/// let v_collected = v_clone.into_iter()
///                          .map(Some)
///                          .collect::<Vec<Option<&i32>>>();
///
/// let v_clone = v_orig.clone();
///
/// // This is the proper no-copy, unsafe way of "transmuting" a `Vec`, without relying on the
/// // data layout. Instead of literally calling `transmute`, we perform a pointer cast, but
/// // in terms of converting the original inner type (`&i32`) to the new one (`Option<&i32>`),
/// // this has all the same caveats. Besides the information provided above, also consult the
/// // [`from_raw_parts`] documentation.
/// let (ptr, len, capacity) = v_clone.into_raw_parts();
/// let v_from_raw = unsafe {
///     Vec::from_raw_parts(ptr.cast::<*mut Option<&i32>>(), len, capacity)
/// };
/// ```
///
/// [`from_raw_parts`]: ../../std/vec/struct.Vec.html#method.from_raw_parts
///
/// Implementing `split_at_mut`:
///
/// ```
/// use std::{slice, mem};
///
/// // There are multiple ways to do this, and there are multiple problems
/// // with the following (transmute) way.
/// fn split_at_mut_transmute<T>(slice: &mut [T], mid: usize)
///                              -> (&mut [T], &mut [T]) {
///     let len = slice.len();
///     assert!(mid <= len);
///     unsafe {
///         let slice2 = mem::transmute::<&mut [T], &mut [T]>(slice);
///         // first: transmute is not type safe; all it checks is that T and
///         // U are of the same size. Second, right here, you have two
///         // mutable references pointing to the same memory.
///         (&mut slice[0..mid], &mut slice2[mid..len])
///     }
/// }
///
/// // This gets rid of the type safety problems; `&mut *` will *only* give
/// // you a `&mut T` from a `&mut T` or `*mut T`.
/// fn split_at_mut_casts<T>(slice: &mut [T], mid: usize)
///                          -> (&mut [T], &mut [T]) {
///     let len = slice.len();
///     assert!(mid <= len);
///     unsafe {
///         let slice2 = &mut *(slice as *mut [T]);
///         // however, you still have two mutable references pointing to
///         // the same memory.
///         (&mut slice[0..mid], &mut slice2[mid..len])
///     }
/// }
///
/// // This is how the standard library does it. This is the best method, if
/// // you need to do something like this
/// fn split_at_stdlib<T>(slice: &mut [T], mid: usize)
///                       -> (&mut [T], &mut [T]) {
///     let len = slice.len();
///     assert!(mid <= len);
///     unsafe {
///         let ptr = slice.as_mut_ptr();
///         // This now has three mutable references pointing at the same
///         // memory. `slice`, the rvalue ret.0, and the rvalue ret.1.
///         // `slice` is never used after `let ptr = ...`, and so one can
///         // treat it as "dead", and therefore, you only have two real
///         // mutable slices.
///         (slice::from_raw_parts_mut(ptr, mid),
///          slice::from_raw_parts_mut(ptr.add(mid), len - mid))
///     }
/// }
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[rustc_allowed_through_unstable_modules = "import this function via `std::mem` instead"]
#[rustc_const_stable(feature = "const_transmute", since = "1.56.0")]
#[rustc_diagnostic_item = "transmute"]
#[rustc_nounwind]
#[rustc_intrinsic]
pub const unsafe fn transmute<Src, Dst>(src: Src) -> Dst;

/// Like [`transmute`], but even less checked at compile-time: rather than
/// giving an error for `size_of::<Src>() != size_of::<Dst>()`, it's
/// **Undefined Behavior** at runtime.
///
/// Prefer normal `transmute` where possible, for the extra checking, since
/// both do exactly the same thing at runtime, if they both compile.
///
/// This is not expected to ever be exposed directly to users, rather it
/// may eventually be exposed through some more-constrained API.
#[rustc_intrinsic_const_stable_indirect]
#[rustc_nounwind]
#[rustc_intrinsic]
pub const unsafe fn transmute_unchecked<Src, Dst>(src: Src) -> Dst;

/// Returns `true` if the actual type given as `T` requires drop
/// glue; returns `false` if the actual type provided for `T`
/// implements `Copy`.
///
/// If the actual type neither requires drop glue nor implements
/// `Copy`, then the return value of this function is unspecified.
///
/// Note that, unlike most intrinsics, this can only be called at compile-time
/// as backends do not have an implementation for it. The only caller (its
/// stable counterpart) wraps this intrinsic call in a `const` block so that
/// backends only see an evaluated constant.
///
/// The stabilized version of this intrinsic is [`mem::needs_drop`](crate::mem::needs_drop).
#[rustc_intrinsic_const_stable_indirect]
#[rustc_nounwind]
#[rustc_intrinsic]
pub const fn needs_drop<T: ?Sized>() -> bool;

/// Calculates the offset from a pointer.
///
/// This is implemented as an intrinsic to avoid converting to and from an
/// integer, since the conversion would throw away aliasing information.
///
/// This can only be used with `Ptr` as a raw pointer type (`*mut` or `*const`)
/// to a `Sized` pointee and with `Delta` as `usize` or `isize`.  Any other
/// instantiations may arbitrarily misbehave, and that's *not* a compiler bug.
///
/// # Safety
///
/// If the computed offset is non-zero, then both the starting and resulting pointer must be
/// either in bounds or at the end of an allocation. If either pointer is out
/// of bounds or arithmetic overflow occurs then this operation is undefined behavior.
///
/// The stabilized version of this intrinsic is [`pointer::offset`].
#[must_use = "returns a new pointer rather than modifying its argument"]
#[rustc_intrinsic_const_stable_indirect]
#[rustc_nounwind]
#[rustc_intrinsic]
pub const unsafe fn offset<Ptr: bounds::BuiltinDeref, Delta>(dst: Ptr, offset: Delta) -> Ptr;

/// Calculates the offset from a pointer, potentially wrapping.
///
/// This is implemented as an intrinsic to avoid converting to and from an
/// integer, since the conversion inhibits certain optimizations.
///
/// # Safety
///
/// Unlike the `offset` intrinsic, this intrinsic does not restrict the
/// resulting pointer to point into or at the end of an allocated
/// object, and it wraps with two's complement arithmetic. The resulting
/// value is not necessarily valid to be used to actually access memory.
///
/// The stabilized version of this intrinsic is [`pointer::wrapping_offset`].
#[must_use = "returns a new pointer rather than modifying its argument"]
#[rustc_intrinsic_const_stable_indirect]
#[rustc_nounwind]
#[rustc_intrinsic]
pub const unsafe fn arith_offset<T>(dst: *const T, offset: isize) -> *const T;

/// Projects to the `index`-th element of `slice_ptr`, as the same kind of pointer
/// as the slice was provided -- so `&mut [T] → &mut T`, `&[T] → &T`,
/// `*mut [T] → *mut T`, or `*const [T] → *const T` -- without a bounds check.
///
/// This is exposed via `<usize as SliceIndex>::get(_unchecked)(_mut)`,
/// and isn't intended to be used elsewhere.
///
/// Expands in MIR to `{&, &mut, &raw const, &raw mut} (*slice_ptr)[index]`,
/// depending on the types involved, so no backend support is needed.
///
/// # Safety
///
/// - `index < PtrMetadata(slice_ptr)`, so the indexing is in-bounds for the slice
/// - the resulting offsetting is in-bounds of the allocation, which is
///   always the case for references, but needs to be upheld manually for pointers
#[rustc_nounwind]
#[rustc_intrinsic]
pub const unsafe fn slice_get_unchecked<
    ItemPtr: bounds::ChangePointee<[T], Pointee = T, Output = SlicePtr>,
    SlicePtr,
    T,
>(
    slice_ptr: SlicePtr,
    index: usize,
) -> ItemPtr;

/// Masks out bits of the pointer according to a mask.
///
/// Note that, unlike most intrinsics, this is safe to call;
/// it does not require an `unsafe` block.
/// Therefore, implementations must not require the user to uphold
/// any safety invariants.
///
/// Consider using [`pointer::mask`] instead.
#[rustc_nounwind]
#[rustc_intrinsic]
pub fn ptr_mask<T>(ptr: *const T, mask: usize) -> *const T;

/// Equivalent to the appropriate `llvm.memcpy.p0i8.0i8.*` intrinsic, with
/// a size of `count` * `size_of::<T>()` and an alignment of `align_of::<T>()`.
///
/// This intrinsic does not have a stable counterpart.
/// # Safety
///
/// The safety requirements are consistent with [`copy_nonoverlapping`]
/// while the read and write behaviors are volatile,
/// which means it will not be optimized out unless `_count` or `size_of::<T>()` is equal to zero.
///
/// [`copy_nonoverlapping`]: ptr::copy_nonoverlapping
#[rustc_intrinsic]
#[rustc_nounwind]
pub unsafe fn volatile_copy_nonoverlapping_memory<T>(dst: *mut T, src: *const T, count: usize);
/// Equivalent to the appropriate `llvm.memmove.p0i8.0i8.*` intrinsic, with
/// a size of `count * size_of::<T>()` and an alignment of `align_of::<T>()`.
///
/// The volatile parameter is set to `true`, so it will not be optimized out
/// unless size is equal to zero.
///
/// This intrinsic does not have a stable counterpart.
#[rustc_intrinsic]
#[rustc_nounwind]
pub unsafe fn volatile_copy_memory<T>(dst: *mut T, src: *const T, count: usize);
/// Equivalent to the appropriate `llvm.memset.p0i8.*` intrinsic, with a
/// size of `count * size_of::<T>()` and an alignment of `align_of::<T>()`.
///
/// This intrinsic does not have a stable counterpart.
/// # Safety
///
/// The safety requirements are consistent with [`write_bytes`] while the write behavior is volatile,
/// which means it will not be optimized out unless `_count` or `size_of::<T>()` is equal to zero.
///
/// [`write_bytes`]: ptr::write_bytes
#[rustc_intrinsic]
#[rustc_nounwind]
pub unsafe fn volatile_set_memory<T>(dst: *mut T, val: u8, count: usize);

/// Performs a volatile load from the `src` pointer.
///
/// The stabilized version of this intrinsic is [`core::ptr::read_volatile`].
#[rustc_intrinsic]
#[rustc_nounwind]
pub unsafe fn volatile_load<T>(src: *const T) -> T;
/// Performs a volatile store to the `dst` pointer.
///
/// The stabilized version of this intrinsic is [`core::ptr::write_volatile`].
#[rustc_intrinsic]
#[rustc_nounwind]
pub unsafe fn volatile_store<T>(dst: *mut T, val: T);

/// Performs a volatile load from the `src` pointer
/// The pointer is not required to be aligned.
///
/// This intrinsic does not have a stable counterpart.
#[rustc_intrinsic]
#[rustc_nounwind]
#[rustc_diagnostic_item = "intrinsics_unaligned_volatile_load"]
pub unsafe fn unaligned_volatile_load<T>(src: *const T) -> T;
/// Performs a volatile store to the `dst` pointer.
/// The pointer is not required to be aligned.
///
/// This intrinsic does not have a stable counterpart.
#[rustc_intrinsic]
#[rustc_nounwind]
#[rustc_diagnostic_item = "intrinsics_unaligned_volatile_store"]
pub unsafe fn unaligned_volatile_store<T>(dst: *mut T, val: T);

/// Returns the square root of an `f16`
///
/// The stabilized version of this intrinsic is
/// [`f16::sqrt`](../../std/primitive.f16.html#method.sqrt)
#[rustc_intrinsic]
#[rustc_nounwind]
pub fn sqrtf16(x: f16) -> f16;
/// Returns the square root of an `f32`
///
/// The stabilized version of this intrinsic is
/// [`f32::sqrt`](../../std/primitive.f32.html#method.sqrt)
#[rustc_intrinsic]
#[rustc_nounwind]
pub fn sqrtf32(x: f32) -> f32;
/// Returns the square root of an `f64`
///
/// The stabilized version of this intrinsic is
/// [`f64::sqrt`](../../std/primitive.f64.html#method.sqrt)
#[rustc_intrinsic]
#[rustc_nounwind]
pub fn sqrtf64(x: f64) -> f64;
/// Returns the square root of an `f128`
///
/// The stabilized version of this intrinsic is
/// [`f128::sqrt`](../../std/primitive.f128.html#method.sqrt)
#[rustc_intrinsic]
#[rustc_nounwind]
pub fn sqrtf128(x: f128) -> f128;

/// Raises an `f16` to an integer power.
///
/// The stabilized version of this intrinsic is
/// [`f16::powi`](../../std/primitive.f16.html#method.powi)
#[rustc_intrinsic]
#[rustc_nounwind]
pub fn powif16(a: f16, x: i32) -> f16;
/// Raises an `f32` to an integer power.
///
/// The stabilized version of this intrinsic is
/// [`f32::powi`](../../std/primitive.f32.html#method.powi)
#[rustc_intrinsic]
#[rustc_nounwind]
pub fn powif32(a: f32, x: i32) -> f32;
/// Raises an `f64` to an integer power.
///
/// The stabilized version of this intrinsic is
/// [`f64::powi`](../../std/primitive.f64.html#method.powi)
#[rustc_intrinsic]
#[rustc_nounwind]
pub fn powif64(a: f64, x: i32) -> f64;
/// Raises an `f128` to an integer power.
///
/// The stabilized version of this intrinsic is
/// [`f128::powi`](../../std/primitive.f128.html#method.powi)
#[rustc_intrinsic]
#[rustc_nounwind]
pub fn powif128(a: f128, x: i32) -> f128;

/// Returns the sine of an `f16`.
///
/// The stabilized version of this intrinsic is
/// [`f16::sin`](../../std/primitive.f16.html#method.sin)
#[rustc_intrinsic]
#[rustc_nounwind]
pub fn sinf16(x: f16) -> f16;
/// Returns the sine of an `f32`.
///
/// The stabilized version of this intrinsic is
/// [`f32::sin`](../../std/primitive.f32.html#method.sin)
#[rustc_intrinsic]
#[rustc_nounwind]
pub fn sinf32(x: f32) -> f32;
/// Returns the sine of an `f64`.
///
/// The stabilized version of this intrinsic is
/// [`f64::sin`](../../std/primitive.f64.html#method.sin)
#[rustc_intrinsic]
#[rustc_nounwind]
pub fn sinf64(x: f64) -> f64;
/// Returns the sine of an `f128`.
///
/// The stabilized version of this intrinsic is
/// [`f128::sin`](../../std/primitive.f128.html#method.sin)
#[rustc_intrinsic]
#[rustc_nounwind]
pub fn sinf128(x: f128) -> f128;

/// Returns the cosine of an `f16`.
///
/// The stabilized version of this intrinsic is
/// [`f16::cos`](../../std/primitive.f16.html#method.cos)
#[rustc_intrinsic]
#[rustc_nounwind]
pub fn cosf16(x: f16) -> f16;
/// Returns the cosine of an `f32`.
///
/// The stabilized version of this intrinsic is
/// [`f32::cos`](../../std/primitive.f32.html#method.cos)
#[rustc_intrinsic]
#[rustc_nounwind]
pub fn cosf32(x: f32) -> f32;
/// Returns the cosine of an `f64`.
///
/// The stabilized version of this intrinsic is
/// [`f64::cos`](../../std/primitive.f64.html#method.cos)
#[rustc_intrinsic]
#[rustc_nounwind]
pub fn cosf64(x: f64) -> f64;
/// Returns the cosine of an `f128`.
///
/// The stabilized version of this intrinsic is
/// [`f128::cos`](../../std/primitive.f128.html#method.cos)
#[rustc_intrinsic]
#[rustc_nounwind]
pub fn cosf128(x: f128) -> f128;

/// Raises an `f16` to an `f16` power.
///
/// The stabilized version of this intrinsic is
/// [`f16::powf`](../../std/primitive.f16.html#method.powf)
#[rustc_intrinsic]
#[rustc_nounwind]
pub fn powf16(a: f16, x: f16) -> f16;
/// Raises an `f32` to an `f32` power.
///
/// The stabilized version of this intrinsic is
/// [`f32::powf`](../../std/primitive.f32.html#method.powf)
#[rustc_intrinsic]
#[rustc_nounwind]
pub fn powf32(a: f32, x: f32) -> f32;
/// Raises an `f64` to an `f64` power.
///
/// The stabilized version of this intrinsic is
/// [`f64::powf`](../../std/primitive.f64.html#method.powf)
#[rustc_intrinsic]
#[rustc_nounwind]
pub fn powf64(a: f64, x: f64) -> f64;
/// Raises an `f128` to an `f128` power.
///
/// The stabilized version of this intrinsic is
/// [`f128::powf`](../../std/primitive.f128.html#method.powf)
#[rustc_intrinsic]
#[rustc_nounwind]
pub fn powf128(a: f128, x: f128) -> f128;

/// Returns the exponential of an `f16`.
///
/// The stabilized version of this intrinsic is
/// [`f16::exp`](../../std/primitive.f16.html#method.exp)
#[rustc_intrinsic]
#[rustc_nounwind]
pub fn expf16(x: f16) -> f16;
/// Returns the exponential of an `f32`.
///
/// The stabilized version of this intrinsic is
/// [`f32::exp`](../../std/primitive.f32.html#method.exp)
#[rustc_intrinsic]
#[rustc_nounwind]
pub fn expf32(x: f32) -> f32;
/// Returns the exponential of an `f64`.
///
/// The stabilized version of this intrinsic is
/// [`f64::exp`](../../std/primitive.f64.html#method.exp)
#[rustc_intrinsic]
#[rustc_nounwind]
pub fn expf64(x: f64) -> f64;
/// Returns the exponential of an `f128`.
///
/// The stabilized version of this intrinsic is
/// [`f128::exp`](../../std/primitive.f128.html#method.exp)
#[rustc_intrinsic]
#[rustc_nounwind]
pub fn expf128(x: f128) -> f128;

/// Returns 2 raised to the power of an `f16`.
///
/// The stabilized version of this intrinsic is
/// [`f16::exp2`](../../std/primitive.f16.html#method.exp2)
#[rustc_intrinsic]
#[rustc_nounwind]
pub fn exp2f16(x: f16) -> f16;
/// Returns 2 raised to the power of an `f32`.
///
/// The stabilized version of this intrinsic is
/// [`f32::exp2`](../../std/primitive.f32.html#method.exp2)
#[rustc_intrinsic]
#[rustc_nounwind]
pub fn exp2f32(x: f32) -> f32;
/// Returns 2 raised to the power of an `f64`.
///
/// The stabilized version of this intrinsic is
/// [`f64::exp2`](../../std/primitive.f64.html#method.exp2)
#[rustc_intrinsic]
#[rustc_nounwind]
pub fn exp2f64(x: f64) -> f64;
/// Returns 2 raised to the power of an `f128`.
///
/// The stabilized version of this intrinsic is
/// [`f128::exp2`](../../std/primitive.f128.html#method.exp2)
#[rustc_intrinsic]
#[rustc_nounwind]
pub fn exp2f128(x: f128) -> f128;

/// Returns the natural logarithm of an `f16`.
///
/// The stabilized version of this intrinsic is
/// [`f16::ln`](../../std/primitive.f16.html#method.ln)
#[rustc_intrinsic]
#[rustc_nounwind]
pub fn logf16(x: f16) -> f16;
/// Returns the natural logarithm of an `f32`.
///
/// The stabilized version of this intrinsic is
/// [`f32::ln`](../../std/primitive.f32.html#method.ln)
#[rustc_intrinsic]
#[rustc_nounwind]
pub fn logf32(x: f32) -> f32;
/// Returns the natural logarithm of an `f64`.
///
/// The stabilized version of this intrinsic is
/// [`f64::ln`](../../std/primitive.f64.html#method.ln)
#[rustc_intrinsic]
#[rustc_nounwind]
pub fn logf64(x: f64) -> f64;
/// Returns the natural logarithm of an `f128`.
///
/// The stabilized version of this intrinsic is
/// [`f128::ln`](../../std/primitive.f128.html#method.ln)
#[rustc_intrinsic]
#[rustc_nounwind]
pub fn logf128(x: f128) -> f128;

/// Returns the base 10 logarithm of an `f16`.
///
/// The stabilized version of this intrinsic is
/// [`f16::log10`](../../std/primitive.f16.html#method.log10)
#[rustc_intrinsic]
#[rustc_nounwind]
pub fn log10f16(x: f16) -> f16;
/// Returns the base 10 logarithm of an `f32`.
///
/// The stabilized version of this intrinsic is
/// [`f32::log10`](../../std/primitive.f32.html#method.log10)
#[rustc_intrinsic]
#[rustc_nounwind]
pub fn log10f32(x: f32) -> f32;
/// Returns the base 10 logarithm of an `f64`.
///
/// The stabilized version of this intrinsic is
/// [`f64::log10`](../../std/primitive.f64.html#method.log10)
#[rustc_intrinsic]
#[rustc_nounwind]
pub fn log10f64(x: f64) -> f64;
/// Returns the base 10 logarithm of an `f128`.
///
/// The stabilized version of this intrinsic is
/// [`f128::log10`](../../std/primitive.f128.html#method.log10)
#[rustc_intrinsic]
#[rustc_nounwind]
pub fn log10f128(x: f128) -> f128;

/// Returns the base 2 logarithm of an `f16`.
///
/// The stabilized version of this intrinsic is
/// [`f16::log2`](../../std/primitive.f16.html#method.log2)
#[rustc_intrinsic]
#[rustc_nounwind]
pub fn log2f16(x: f16) -> f16;
/// Returns the base 2 logarithm of an `f32`.
///
/// The stabilized version of this intrinsic is
/// [`f32::log2`](../../std/primitive.f32.html#method.log2)
#[rustc_intrinsic]
#[rustc_nounwind]
pub fn log2f32(x: f32) -> f32;
/// Returns the base 2 logarithm of an `f64`.
///
/// The stabilized version of this intrinsic is
/// [`f64::log2`](../../std/primitive.f64.html#method.log2)
#[rustc_intrinsic]
#[rustc_nounwind]
pub fn log2f64(x: f64) -> f64;
/// Returns the base 2 logarithm of an `f128`.
///
/// The stabilized version of this intrinsic is
/// [`f128::log2`](../../std/primitive.f128.html#method.log2)
#[rustc_intrinsic]
#[rustc_nounwind]
pub fn log2f128(x: f128) -> f128;

/// Returns `a * b + c` for `f16` values.
///
/// The stabilized version of this intrinsic is
/// [`f16::mul_add`](../../std/primitive.f16.html#method.mul_add)
#[rustc_intrinsic_const_stable_indirect]
#[rustc_intrinsic]
#[rustc_nounwind]
pub const fn fmaf16(a: f16, b: f16, c: f16) -> f16;
/// Returns `a * b + c` for `f32` values.
///
/// The stabilized version of this intrinsic is
/// [`f32::mul_add`](../../std/primitive.f32.html#method.mul_add)
#[rustc_intrinsic_const_stable_indirect]
#[rustc_intrinsic]
#[rustc_nounwind]
pub const fn fmaf32(a: f32, b: f32, c: f32) -> f32;
/// Returns `a * b + c` for `f64` values.
///
/// The stabilized version of this intrinsic is
/// [`f64::mul_add`](../../std/primitive.f64.html#method.mul_add)
#[rustc_intrinsic_const_stable_indirect]
#[rustc_intrinsic]
#[rustc_nounwind]
pub const fn fmaf64(a: f64, b: f64, c: f64) -> f64;
/// Returns `a * b + c` for `f128` values.
///
/// The stabilized version of this intrinsic is
/// [`f128::mul_add`](../../std/primitive.f128.html#method.mul_add)
#[rustc_intrinsic_const_stable_indirect]
#[rustc_intrinsic]
#[rustc_nounwind]
pub const fn fmaf128(a: f128, b: f128, c: f128) -> f128;

/// Returns `a * b + c` for `f16` values, non-deterministically executing
/// either a fused multiply-add or two operations with rounding of the
/// intermediate result.
///
/// The operation is fused if the code generator determines that target
/// instruction set has support for a fused operation, and that the fused
/// operation is more efficient than the equivalent, separate pair of mul
/// and add instructions. It is unspecified whether or not a fused operation
/// is selected, and that may depend on optimization level and context, for
/// example.
#[rustc_intrinsic]
#[rustc_nounwind]
pub const fn fmuladdf16(a: f16, b: f16, c: f16) -> f16;
/// Returns `a * b + c` for `f32` values, non-deterministically executing
/// either a fused multiply-add or two operations with rounding of the
/// intermediate result.
///
/// The operation is fused if the code generator determines that target
/// instruction set has support for a fused operation, and that the fused
/// operation is more efficient than the equivalent, separate pair of mul
/// and add instructions. It is unspecified whether or not a fused operation
/// is selected, and that may depend on optimization level and context, for
/// example.
#[rustc_intrinsic]
#[rustc_nounwind]
pub const fn fmuladdf32(a: f32, b: f32, c: f32) -> f32;
/// Returns `a * b + c` for `f64` values, non-deterministically executing
/// either a fused multiply-add or two operations with rounding of the
/// intermediate result.
///
/// The operation is fused if the code generator determines that target
/// instruction set has support for a fused operation, and that the fused
/// operation is more efficient than the equivalent, separate pair of mul
/// and add instructions. It is unspecified whether or not a fused operation
/// is selected, and that may depend on optimization level and context, for
/// example.
#[rustc_intrinsic]
#[rustc_nounwind]
pub const fn fmuladdf64(a: f64, b: f64, c: f64) -> f64;
/// Returns `a * b + c` for `f128` values, non-deterministically executing
/// either a fused multiply-add or two operations with rounding of the
/// intermediate result.
///
/// The operation is fused if the code generator determines that target
/// instruction set has support for a fused operation, and that the fused
/// operation is more efficient than the equivalent, separate pair of mul
/// and add instructions. It is unspecified whether or not a fused operation
/// is selected, and that may depend on optimization level and context, for
/// example.
#[rustc_intrinsic]
#[rustc_nounwind]
pub const fn fmuladdf128(a: f128, b: f128, c: f128) -> f128;

/// Returns the largest integer less than or equal to an `f16`.
///
/// The stabilized version of this intrinsic is
/// [`f16::floor`](../../std/primitive.f16.html#method.floor)
#[rustc_intrinsic_const_stable_indirect]
#[rustc_intrinsic]
#[rustc_nounwind]
pub const fn floorf16(x: f16) -> f16;
/// Returns the largest integer less than or equal to an `f32`.
///
/// The stabilized version of this intrinsic is
/// [`f32::floor`](../../std/primitive.f32.html#method.floor)
#[rustc_intrinsic_const_stable_indirect]
#[rustc_intrinsic]
#[rustc_nounwind]
pub const fn floorf32(x: f32) -> f32;
/// Returns the largest integer less than or equal to an `f64`.
///
/// The stabilized version of this intrinsic is
/// [`f64::floor`](../../std/primitive.f64.html#method.floor)
#[rustc_intrinsic_const_stable_indirect]
#[rustc_intrinsic]
#[rustc_nounwind]
pub const fn floorf64(x: f64) -> f64;
/// Returns the largest integer less than or equal to an `f128`.
///
/// The stabilized version of this intrinsic is
/// [`f128::floor`](../../std/primitive.f128.html#method.floor)
#[rustc_intrinsic_const_stable_indirect]
#[rustc_intrinsic]
#[rustc_nounwind]
pub const fn floorf128(x: f128) -> f128;

/// Returns the smallest integer greater than or equal to an `f16`.
///
/// The stabilized version of this intrinsic is
/// [`f16::ceil`](../../std/primitive.f16.html#method.ceil)
#[rustc_intrinsic_const_stable_indirect]
#[rustc_intrinsic]
#[rustc_nounwind]
pub const fn ceilf16(x: f16) -> f16;
/// Returns the smallest integer greater than or equal to an `f32`.
///
/// The stabilized version of this intrinsic is
/// [`f32::ceil`](../../std/primitive.f32.html#method.ceil)
#[rustc_intrinsic_const_stable_indirect]
#[rustc_intrinsic]
#[rustc_nounwind]
pub const fn ceilf32(x: f32) -> f32;
/// Returns the smallest integer greater than or equal to an `f64`.
///
/// The stabilized version of this intrinsic is
/// [`f64::ceil`](../../std/primitive.f64.html#method.ceil)
#[rustc_intrinsic_const_stable_indirect]
#[rustc_intrinsic]
#[rustc_nounwind]
pub const fn ceilf64(x: f64) -> f64;
/// Returns the smallest integer greater than or equal to an `f128`.
///
/// The stabilized version of this intrinsic is
/// [`f128::ceil`](../../std/primitive.f128.html#method.ceil)
#[rustc_intrinsic_const_stable_indirect]
#[rustc_intrinsic]
#[rustc_nounwind]
pub const fn ceilf128(x: f128) -> f128;

/// Returns the integer part of an `f16`.
///
/// The stabilized version of this intrinsic is
/// [`f16::trunc`](../../std/primitive.f16.html#method.trunc)
#[rustc_intrinsic_const_stable_indirect]
#[rustc_intrinsic]
#[rustc_nounwind]
pub const fn truncf16(x: f16) -> f16;
/// Returns the integer part of an `f32`.
///
/// The stabilized version of this intrinsic is
/// [`f32::trunc`](../../std/primitive.f32.html#method.trunc)
#[rustc_intrinsic_const_stable_indirect]
#[rustc_intrinsic]
#[rustc_nounwind]
pub const fn truncf32(x: f32) -> f32;
/// Returns the integer part of an `f64`.
///
/// The stabilized version of this intrinsic is
/// [`f64::trunc`](../../std/primitive.f64.html#method.trunc)
#[rustc_intrinsic_const_stable_indirect]
#[rustc_intrinsic]
#[rustc_nounwind]
pub const fn truncf64(x: f64) -> f64;
/// Returns the integer part of an `f128`.
///
/// The stabilized version of this intrinsic is
/// [`f128::trunc`](../../std/primitive.f128.html#method.trunc)
#[rustc_intrinsic_const_stable_indirect]
#[rustc_intrinsic]
#[rustc_nounwind]
pub const fn truncf128(x: f128) -> f128;

/// Returns the nearest integer to an `f16`. Rounds half-way cases to the number with an even
/// least significant digit.
///
/// The stabilized version of this intrinsic is
/// [`f16::round_ties_even`](../../std/primitive.f16.html#method.round_ties_even)
#[rustc_intrinsic_const_stable_indirect]
#[rustc_intrinsic]
#[rustc_nounwind]
pub const fn round_ties_even_f16(x: f16) -> f16;

/// Returns the nearest integer to an `f32`. Rounds half-way cases to the number with an even
/// least significant digit.
///
/// The stabilized version of this intrinsic is
/// [`f32::round_ties_even`](../../std/primitive.f32.html#method.round_ties_even)
#[rustc_intrinsic_const_stable_indirect]
#[rustc_intrinsic]
#[rustc_nounwind]
pub const fn round_ties_even_f32(x: f32) -> f32;

/// Returns the nearest integer to an `f64`. Rounds half-way cases to the number with an even
/// least significant digit.
///
/// The stabilized version of this intrinsic is
/// [`f64::round_ties_even`](../../std/primitive.f64.html#method.round_ties_even)
#[rustc_intrinsic_const_stable_indirect]
#[rustc_intrinsic]
#[rustc_nounwind]
pub const fn round_ties_even_f64(x: f64) -> f64;

/// Returns the nearest integer to an `f128`. Rounds half-way cases to the number with an even
/// least significant digit.
///
/// The stabilized version of this intrinsic is
/// [`f128::round_ties_even`](../../std/primitive.f128.html#method.round_ties_even)
#[rustc_intrinsic_const_stable_indirect]
#[rustc_intrinsic]
#[rustc_nounwind]
pub const fn round_ties_even_f128(x: f128) -> f128;

/// Returns the nearest integer to an `f16`. Rounds half-way cases away from zero.
///
/// The stabilized version of this intrinsic is
/// [`f16::round`](../../std/primitive.f16.html#method.round)
#[rustc_intrinsic_const_stable_indirect]
#[rustc_intrinsic]
#[rustc_nounwind]
pub const fn roundf16(x: f16) -> f16;
/// Returns the nearest integer to an `f32`. Rounds half-way cases away from zero.
///
/// The stabilized version of this intrinsic is
/// [`f32::round`](../../std/primitive.f32.html#method.round)
#[rustc_intrinsic_const_stable_indirect]
#[rustc_intrinsic]
#[rustc_nounwind]
pub const fn roundf32(x: f32) -> f32;
/// Returns the nearest integer to an `f64`. Rounds half-way cases away from zero.
///
/// The stabilized version of this intrinsic is
/// [`f64::round`](../../std/primitive.f64.html#method.round)
#[rustc_intrinsic_const_stable_indirect]
#[rustc_intrinsic]
#[rustc_nounwind]
pub const fn roundf64(x: f64) -> f64;
/// Returns the nearest integer to an `f128`. Rounds half-way cases away from zero.
///
/// The stabilized version of this intrinsic is
/// [`f128::round`](../../std/primitive.f128.html#method.round)
#[rustc_intrinsic_const_stable_indirect]
#[rustc_intrinsic]
#[rustc_nounwind]
pub const fn roundf128(x: f128) -> f128;

/// Float addition that allows optimizations based on algebraic rules.
/// Requires that inputs and output of the operation are finite, causing UB otherwise.
///
/// This intrinsic does not have a stable counterpart.
#[rustc_intrinsic]
#[rustc_nounwind]
pub unsafe fn fadd_fast<T: bounds::FloatPrimitive>(a: T, b: T) -> T;

/// Float subtraction that allows optimizations based on algebraic rules.
/// Requires that inputs and output of the operation are finite, causing UB otherwise.
///
/// This intrinsic does not have a stable counterpart.
#[rustc_intrinsic]
#[rustc_nounwind]
pub unsafe fn fsub_fast<T: bounds::FloatPrimitive>(a: T, b: T) -> T;

/// Float multiplication that allows optimizations based on algebraic rules.
/// Requires that inputs and output of the operation are finite, causing UB otherwise.
///
/// This intrinsic does not have a stable counterpart.
#[rustc_intrinsic]
#[rustc_nounwind]
pub unsafe fn fmul_fast<T: bounds::FloatPrimitive>(a: T, b: T) -> T;

/// Float division that allows optimizations based on algebraic rules.
/// Requires that inputs and output of the operation are finite, causing UB otherwise.
///
/// This intrinsic does not have a stable counterpart.
#[rustc_intrinsic]
#[rustc_nounwind]
pub unsafe fn fdiv_fast<T: bounds::FloatPrimitive>(a: T, b: T) -> T;

/// Float remainder that allows optimizations based on algebraic rules.
/// Requires that inputs and output of the operation are finite, causing UB otherwise.
///
/// This intrinsic does not have a stable counterpart.
#[rustc_intrinsic]
#[rustc_nounwind]
pub unsafe fn frem_fast<T: bounds::FloatPrimitive>(a: T, b: T) -> T;

/// Converts with LLVM’s fptoui/fptosi, which may return undef for values out of range
/// (<https://github.com/rust-lang/rust/issues/10184>)
///
/// Stabilized as [`f32::to_int_unchecked`] and [`f64::to_int_unchecked`].
#[rustc_intrinsic]
#[rustc_nounwind]
pub unsafe fn float_to_int_unchecked<Float: bounds::FloatPrimitive, Int: Copy>(value: Float)
-> Int;

/// Float addition that allows optimizations based on algebraic rules.
///
/// Stabilized as [`f16::algebraic_add`], [`f32::algebraic_add`], [`f64::algebraic_add`] and [`f128::algebraic_add`].
#[rustc_intrinsic_const_stable_indirect]
#[rustc_nounwind]
#[rustc_intrinsic]
pub const fn fadd_algebraic<T: bounds::FloatPrimitive>(a: T, b: T) -> T;

/// Float subtraction that allows optimizations based on algebraic rules.
///
/// Stabilized as [`f16::algebraic_sub`], [`f32::algebraic_sub`], [`f64::algebraic_sub`] and [`f128::algebraic_sub`].
#[rustc_intrinsic_const_stable_indirect]
#[rustc_nounwind]
#[rustc_intrinsic]
pub const fn fsub_algebraic<T: bounds::FloatPrimitive>(a: T, b: T) -> T;

/// Float multiplication that allows optimizations based on algebraic rules.
///
/// Stabilized as [`f16::algebraic_mul`], [`f32::algebraic_mul`], [`f64::algebraic_mul`] and [`f128::algebraic_mul`].
#[rustc_intrinsic_const_stable_indirect]
#[rustc_nounwind]
#[rustc_intrinsic]
pub const fn fmul_algebraic<T: bounds::FloatPrimitive>(a: T, b: T) -> T;

/// Float division that allows optimizations based on algebraic rules.
///
/// Stabilized as [`f16::algebraic_div`], [`f32::algebraic_div`], [`f64::algebraic_div`] and [`f128::algebraic_div`].
#[rustc_intrinsic_const_stable_indirect]
#[rustc_nounwind]
#[rustc_intrinsic]
pub const fn fdiv_algebraic<T: bounds::FloatPrimitive>(a: T, b: T) -> T;

/// Float remainder that allows optimizations based on algebraic rules.
///
/// Stabilized as [`f16::algebraic_rem`], [`f32::algebraic_rem`], [`f64::algebraic_rem`] and [`f128::algebraic_rem`].
#[rustc_intrinsic_const_stable_indirect]
#[rustc_nounwind]
#[rustc_intrinsic]
pub const fn frem_algebraic<T: bounds::FloatPrimitive>(a: T, b: T) -> T;

/// Returns the number of bits set in an integer type `T`
///
/// Note that, unlike most intrinsics, this is safe to call;
/// it does not require an `unsafe` block.
/// Therefore, implementations must not require the user to uphold
/// any safety invariants.
///
/// The stabilized versions of this intrinsic are available on the integer
/// primitives via the `count_ones` method. For example,
/// [`u32::count_ones`]
#[rustc_intrinsic_const_stable_indirect]
#[rustc_nounwind]
#[rustc_intrinsic]
pub const fn ctpop<T: Copy>(x: T) -> u32;

/// Returns the number of leading unset bits (zeroes) in an integer type `T`.
///
/// Note that, unlike most intrinsics, this is safe to call;
/// it does not require an `unsafe` block.
/// Therefore, implementations must not require the user to uphold
/// any safety invariants.
///
/// The stabilized versions of this intrinsic are available on the integer
/// primitives via the `leading_zeros` method. For example,
/// [`u32::leading_zeros`]
///
/// # Examples
///
/// ```
/// #![feature(core_intrinsics)]
/// # #![allow(internal_features)]
///
/// use std::intrinsics::ctlz;
///
/// let x = 0b0001_1100_u8;
/// let num_leading = ctlz(x);
/// assert_eq!(num_leading, 3);
/// ```
///
/// An `x` with value `0` will return the bit width of `T`.
///
/// ```
/// #![feature(core_intrinsics)]
/// # #![allow(internal_features)]
///
/// use std::intrinsics::ctlz;
///
/// let x = 0u16;
/// let num_leading = ctlz(x);
/// assert_eq!(num_leading, 16);
/// ```
#[rustc_intrinsic_const_stable_indirect]
#[rustc_nounwind]
#[rustc_intrinsic]
pub const fn ctlz<T: Copy>(x: T) -> u32;

/// Like `ctlz`, but extra-unsafe as it returns `undef` when
/// given an `x` with value `0`.
///
/// This intrinsic does not have a stable counterpart.
///
/// # Examples
///
/// ```
/// #![feature(core_intrinsics)]
/// # #![allow(internal_features)]
///
/// use std::intrinsics::ctlz_nonzero;
///
/// let x = 0b0001_1100_u8;
/// let num_leading = unsafe { ctlz_nonzero(x) };
/// assert_eq!(num_leading, 3);
/// ```
#[rustc_intrinsic_const_stable_indirect]
#[rustc_nounwind]
#[rustc_intrinsic]
pub const unsafe fn ctlz_nonzero<T: Copy>(x: T) -> u32;

/// Returns the number of trailing unset bits (zeroes) in an integer type `T`.
///
/// Note that, unlike most intrinsics, this is safe to call;
/// it does not require an `unsafe` block.
/// Therefore, implementations must not require the user to uphold
/// any safety invariants.
///
/// The stabilized versions of this intrinsic are available on the integer
/// primitives via the `trailing_zeros` method. For example,
/// [`u32::trailing_zeros`]
///
/// # Examples
///
/// ```
/// #![feature(core_intrinsics)]
/// # #![allow(internal_features)]
///
/// use std::intrinsics::cttz;
///
/// let x = 0b0011_1000_u8;
/// let num_trailing = cttz(x);
/// assert_eq!(num_trailing, 3);
/// ```
///
/// An `x` with value `0` will return the bit width of `T`:
///
/// ```
/// #![feature(core_intrinsics)]
/// # #![allow(internal_features)]
///
/// use std::intrinsics::cttz;
///
/// let x = 0u16;
/// let num_trailing = cttz(x);
/// assert_eq!(num_trailing, 16);
/// ```
#[rustc_intrinsic_const_stable_indirect]
#[rustc_nounwind]
#[rustc_intrinsic]
pub const fn cttz<T: Copy>(x: T) -> u32;

/// Like `cttz`, but extra-unsafe as it returns `undef` when
/// given an `x` with value `0`.
///
/// This intrinsic does not have a stable counterpart.
///
/// # Examples
///
/// ```
/// #![feature(core_intrinsics)]
/// # #![allow(internal_features)]
///
/// use std::intrinsics::cttz_nonzero;
///
/// let x = 0b0011_1000_u8;
/// let num_trailing = unsafe { cttz_nonzero(x) };
/// assert_eq!(num_trailing, 3);
/// ```
#[rustc_intrinsic_const_stable_indirect]
#[rustc_nounwind]
#[rustc_intrinsic]
pub const unsafe fn cttz_nonzero<T: Copy>(x: T) -> u32;

/// Reverses the bytes in an integer type `T`.
///
/// Note that, unlike most intrinsics, this is safe to call;
/// it does not require an `unsafe` block.
/// Therefore, implementations must not require the user to uphold
/// any safety invariants.
///
/// The stabilized versions of this intrinsic are available on the integer
/// primitives via the `swap_bytes` method. For example,
/// [`u32::swap_bytes`]
#[rustc_intrinsic_const_stable_indirect]
#[rustc_nounwind]
#[rustc_intrinsic]
pub const fn bswap<T: Copy>(x: T) -> T;

/// Reverses the bits in an integer type `T`.
///
/// Note that, unlike most intrinsics, this is safe to call;
/// it does not require an `unsafe` block.
/// Therefore, implementations must not require the user to uphold
/// any safety invariants.
///
/// The stabilized versions of this intrinsic are available on the integer
/// primitives via the `reverse_bits` method. For example,
/// [`u32::reverse_bits`]
#[rustc_intrinsic_const_stable_indirect]
#[rustc_nounwind]
#[rustc_intrinsic]
pub const fn bitreverse<T: Copy>(x: T) -> T;

/// Does a three-way comparison between the two arguments,
/// which must be of character or integer (signed or unsigned) type.
///
/// This was originally added because it greatly simplified the MIR in `cmp`
/// implementations, and then LLVM 20 added a backend intrinsic for it too.
///
/// The stabilized version of this intrinsic is [`Ord::cmp`].
#[rustc_intrinsic_const_stable_indirect]
#[rustc_nounwind]
#[rustc_intrinsic]
pub const fn three_way_compare<T: Copy>(lhs: T, rhss: T) -> crate::cmp::Ordering;

/// Combine two values which have no bits in common.
///
/// This allows the backend to implement it as `a + b` *or* `a | b`,
/// depending which is easier to implement on a specific target.
///
/// # Safety
///
/// Requires that `(a & b) == 0`, or equivalently that `(a | b) == (a + b)`.
///
/// Otherwise it's immediate UB.
#[rustc_const_unstable(feature = "disjoint_bitor", issue = "135758")]
#[rustc_nounwind]
#[rustc_intrinsic]
#[track_caller]
#[miri::intrinsic_fallback_is_spec] // the fallbacks all `assume` to tell Miri
#[ferrocene::annotation(
    "All calls to this function are replaced during code generation unless the target doesn't have this intrinsic. In the latter case, the body of this function remains unchanged, meaning that it calls `intrinsics::fallback::DisjointBitOr::disjoint_bitor` which is thoroughly tested.  The correctness of the code generation is tested in `tests/codegen-llvm/intrinsics/disjoint_bitor.rs`"
)]
#[ferrocene::prevalidated]
pub const unsafe fn disjoint_bitor<T: [const] fallback::DisjointBitOr>(a: T, b: T) -> T {
    // SAFETY: same preconditions as this function.
    unsafe { fallback::DisjointBitOr::disjoint_bitor(a, b) }
}

/// Performs checked integer addition.
///
/// Note that, unlike most intrinsics, this is safe to call;
/// it does not require an `unsafe` block.
/// Therefore, implementations must not require the user to uphold
/// any safety invariants.
///
/// The stabilized versions of this intrinsic are available on the integer
/// primitives via the `overflowing_add` method. For example,
/// [`u32::overflowing_add`]
#[rustc_intrinsic_const_stable_indirect]
#[rustc_nounwind]
#[rustc_intrinsic]
pub const fn add_with_overflow<T: Copy>(x: T, y: T) -> (T, bool);

/// Performs checked integer subtraction
///
/// Note that, unlike most intrinsics, this is safe to call;
/// it does not require an `unsafe` block.
/// Therefore, implementations must not require the user to uphold
/// any safety invariants.
///
/// The stabilized versions of this intrinsic are available on the integer
/// primitives via the `overflowing_sub` method. For example,
/// [`u32::overflowing_sub`]
#[rustc_intrinsic_const_stable_indirect]
#[rustc_nounwind]
#[rustc_intrinsic]
pub const fn sub_with_overflow<T: Copy>(x: T, y: T) -> (T, bool);

/// Performs checked integer multiplication
///
/// Note that, unlike most intrinsics, this is safe to call;
/// it does not require an `unsafe` block.
/// Therefore, implementations must not require the user to uphold
/// any safety invariants.
///
/// The stabilized versions of this intrinsic are available on the integer
/// primitives via the `overflowing_mul` method. For example,
/// [`u32::overflowing_mul`]
#[rustc_intrinsic_const_stable_indirect]
#[rustc_nounwind]
#[rustc_intrinsic]
pub const fn mul_with_overflow<T: Copy>(x: T, y: T) -> (T, bool);

/// Performs full-width multiplication and addition with a carry:
/// `multiplier * multiplicand + addend + carry`.
///
/// This is possible without any overflow.  For `uN`:
///    MAX * MAX + MAX + MAX
/// => (2ⁿ-1) × (2ⁿ-1) + (2ⁿ-1) + (2ⁿ-1)
/// => (2²ⁿ - 2ⁿ⁺¹ + 1) + (2ⁿ⁺¹ - 2)
/// => 2²ⁿ - 1
///
/// For `iN`, the upper bound is MIN * MIN + MAX + MAX => 2²ⁿ⁻² + 2ⁿ - 2,
/// and the lower bound is MAX * MIN + MIN + MIN => -2²ⁿ⁻² - 2ⁿ + 2ⁿ⁺¹.
///
/// This currently supports unsigned integers *only*, no signed ones.
/// The stabilized versions of this intrinsic are available on integers.
#[ferrocene::annotation(
    "All calls to this function are replaced during code generation unless the target doesn't have this intrinsic. In the latter case, the body of this function remains unchanged, meaning that it calls `intrinsics::fallback::CarryingMulAdd::carrying_mul_add` which is thoroughly tested.  The correctness of the code generation is tested in `tests/codegen-llvm/intrinsics/carrying_mul_add.rs`"
)]
#[unstable(feature = "core_intrinsics", issue = "none")]
#[rustc_const_unstable(feature = "const_carrying_mul_add", issue = "85532")]
#[rustc_nounwind]
#[rustc_intrinsic]
#[miri::intrinsic_fallback_is_spec]
#[ferrocene::prevalidated]
pub const fn carrying_mul_add<T: [const] fallback::CarryingMulAdd<Unsigned = U>, U>(
    multiplier: T,
    multiplicand: T,
    addend: T,
    carry: T,
) -> (U, T) {
    multiplier.carrying_mul_add(multiplicand, addend, carry)
}

/// Performs an exact division, resulting in undefined behavior where
/// `x % y != 0` or `y == 0` or `x == T::MIN && y == -1`
///
/// This intrinsic does not have a stable counterpart.
#[rustc_intrinsic_const_stable_indirect]
#[rustc_nounwind]
#[rustc_intrinsic]
pub const unsafe fn exact_div<T: Copy>(x: T, y: T) -> T;

/// Performs an unchecked division, resulting in undefined behavior
/// where `y == 0` or `x == T::MIN && y == -1`
///
/// Safe wrappers for this intrinsic are available on the integer
/// primitives via the `checked_div` method. For example,
/// [`u32::checked_div`]
#[rustc_intrinsic_const_stable_indirect]
#[rustc_nounwind]
#[rustc_intrinsic]
pub const unsafe fn unchecked_div<T: Copy>(x: T, y: T) -> T;
/// Returns the remainder of an unchecked division, resulting in
/// undefined behavior when `y == 0` or `x == T::MIN && y == -1`
///
/// Safe wrappers for this intrinsic are available on the integer
/// primitives via the `checked_rem` method. For example,
/// [`u32::checked_rem`]
#[rustc_intrinsic_const_stable_indirect]
#[rustc_nounwind]
#[rustc_intrinsic]
pub const unsafe fn unchecked_rem<T: Copy>(x: T, y: T) -> T;

/// Performs an unchecked left shift, resulting in undefined behavior when
/// `y < 0` or `y >= N`, where N is the width of T in bits.
///
/// Safe wrappers for this intrinsic are available on the integer
/// primitives via the `checked_shl` method. For example,
/// [`u32::checked_shl`]
#[rustc_intrinsic_const_stable_indirect]
#[rustc_nounwind]
#[rustc_intrinsic]
pub const unsafe fn unchecked_shl<T: Copy, U: Copy>(x: T, y: U) -> T;
/// Performs an unchecked right shift, resulting in undefined behavior when
/// `y < 0` or `y >= N`, where N is the width of T in bits.
///
/// Safe wrappers for this intrinsic are available on the integer
/// primitives via the `checked_shr` method. For example,
/// [`u32::checked_shr`]
#[rustc_intrinsic_const_stable_indirect]
#[rustc_nounwind]
#[rustc_intrinsic]
pub const unsafe fn unchecked_shr<T: Copy, U: Copy>(x: T, y: U) -> T;

/// Returns the result of an unchecked addition, resulting in
/// undefined behavior when `x + y > T::MAX` or `x + y < T::MIN`.
///
/// The stable counterpart of this intrinsic is `unchecked_add` on the various
/// integer types, such as [`u16::unchecked_add`] and [`i64::unchecked_add`].
#[rustc_intrinsic_const_stable_indirect]
#[rustc_nounwind]
#[rustc_intrinsic]
pub const unsafe fn unchecked_add<T: Copy>(x: T, y: T) -> T;

/// Returns the result of an unchecked subtraction, resulting in
/// undefined behavior when `x - y > T::MAX` or `x - y < T::MIN`.
///
/// The stable counterpart of this intrinsic is `unchecked_sub` on the various
/// integer types, such as [`u16::unchecked_sub`] and [`i64::unchecked_sub`].
#[rustc_intrinsic_const_stable_indirect]
#[rustc_nounwind]
#[rustc_intrinsic]
pub const unsafe fn unchecked_sub<T: Copy>(x: T, y: T) -> T;

/// Returns the result of an unchecked multiplication, resulting in
/// undefined behavior when `x * y > T::MAX` or `x * y < T::MIN`.
///
/// The stable counterpart of this intrinsic is `unchecked_mul` on the various
/// integer types, such as [`u16::unchecked_mul`] and [`i64::unchecked_mul`].
#[rustc_intrinsic_const_stable_indirect]
#[rustc_nounwind]
#[rustc_intrinsic]
pub const unsafe fn unchecked_mul<T: Copy>(x: T, y: T) -> T;

/// Performs rotate left.
///
/// Note that, unlike most intrinsics, this is safe to call;
/// it does not require an `unsafe` block.
/// Therefore, implementations must not require the user to uphold
/// any safety invariants.
///
/// The stabilized versions of this intrinsic are available on the integer
/// primitives via the `rotate_left` method. For example,
/// [`u32::rotate_left`]
#[rustc_intrinsic_const_stable_indirect]
#[rustc_nounwind]
#[rustc_intrinsic]
#[rustc_allow_const_fn_unstable(const_trait_impl, funnel_shifts)]
#[miri::intrinsic_fallback_is_spec]
#[ferrocene::prevalidated]
pub const fn rotate_left<T: [const] fallback::FunnelShift>(x: T, shift: u32) -> T {
    // Make sure to call the intrinsic for `funnel_shl`, not the fallback impl.
    // SAFETY: we modulo `shift` so that the result is definitely less than the size of
    // `T` in bits.
    unsafe { unchecked_funnel_shl(x, x, shift % (mem::size_of::<T>() as u32 * 8)) }
}

/// Performs rotate right.
///
/// Note that, unlike most intrinsics, this is safe to call;
/// it does not require an `unsafe` block.
/// Therefore, implementations must not require the user to uphold
/// any safety invariants.
///
/// The stabilized versions of this intrinsic are available on the integer
/// primitives via the `rotate_right` method. For example,
/// [`u32::rotate_right`]
#[rustc_intrinsic_const_stable_indirect]
#[rustc_nounwind]
#[rustc_intrinsic]
#[rustc_allow_const_fn_unstable(const_trait_impl, funnel_shifts)]
#[miri::intrinsic_fallback_is_spec]
#[ferrocene::prevalidated]
pub const fn rotate_right<T: [const] fallback::FunnelShift>(x: T, shift: u32) -> T {
    // Make sure to call the intrinsic for `funnel_shr`, not the fallback impl.
    // SAFETY: we modulo `shift` so that the result is definitely less than the size of
    // `T` in bits.
    unsafe { unchecked_funnel_shr(x, x, shift % (mem::size_of::<T>() as u32 * 8)) }
}

/// Wrapping (modular) addition. Computes `a + b`,
/// wrapping around at the boundary of the type.
///
/// Note that, unlike most intrinsics, this is safe to call;
/// it does not require an `unsafe` block.
/// Therefore, implementations must not require the user to uphold
/// any safety invariants.
///
/// The stabilized versions of this intrinsic are available on the integer
/// primitives via the `wrapping_add` method. For example,
/// [`u32::wrapping_add`]
#[rustc_intrinsic_const_stable_indirect]
#[rustc_nounwind]
#[rustc_intrinsic]
pub const fn wrapping_add<T: Copy>(a: T, b: T) -> T;
/// Wrapping (modular) subtraction. Computes `a - b`,
/// wrapping around at the boundary of the type.
///
/// Note that, unlike most intrinsics, this is safe to call;
/// it does not require an `unsafe` block.
/// Therefore, implementations must not require the user to uphold
/// any safety invariants.
///
/// The stabilized versions of this intrinsic are available on the integer
/// primitives via the `wrapping_sub` method. For example,
/// [`u32::wrapping_sub`]
#[rustc_intrinsic_const_stable_indirect]
#[rustc_nounwind]
#[rustc_intrinsic]
pub const fn wrapping_sub<T: Copy>(a: T, b: T) -> T;
/// Wrapping (modular) multiplication. Computes `a *
/// b`, wrapping around at the boundary of the type.
///
/// Note that, unlike most intrinsics, this is safe to call;
/// it does not require an `unsafe` block.
/// Therefore, implementations must not require the user to uphold
/// any safety invariants.
///
/// The stabilized versions of this intrinsic are available on the integer
/// primitives via the `wrapping_mul` method. For example,
/// [`u32::wrapping_mul`]
#[rustc_intrinsic_const_stable_indirect]
#[rustc_nounwind]
#[rustc_intrinsic]
pub const fn wrapping_mul<T: Copy>(a: T, b: T) -> T;

/// Computes `a + b`, saturating at numeric bounds.
///
/// Note that, unlike most intrinsics, this is safe to call;
/// it does not require an `unsafe` block.
/// Therefore, implementations must not require the user to uphold
/// any safety invariants.
///
/// The stabilized versions of this intrinsic are available on the integer
/// primitives via the `saturating_add` method. For example,
/// [`u32::saturating_add`]
#[rustc_intrinsic_const_stable_indirect]
#[rustc_nounwind]
#[rustc_intrinsic]
pub const fn saturating_add<T: Copy>(a: T, b: T) -> T;
/// Computes `a - b`, saturating at numeric bounds.
///
/// Note that, unlike most intrinsics, this is safe to call;
/// it does not require an `unsafe` block.
/// Therefore, implementations must not require the user to uphold
/// any safety invariants.
///
/// The stabilized versions of this intrinsic are available on the integer
/// primitives via the `saturating_sub` method. For example,
/// [`u32::saturating_sub`]
#[rustc_intrinsic_const_stable_indirect]
#[rustc_nounwind]
#[rustc_intrinsic]
pub const fn saturating_sub<T: Copy>(a: T, b: T) -> T;

/// Funnel Shift left.
///
/// Concatenates `a` and `b` (with `a` in the most significant half),
/// creating an integer twice as wide. Then shift this integer left
/// by `shift`), and extract the most significant half. If `a` and `b`
/// are the same, this is equivalent to a rotate left operation.
///
/// It is undefined behavior if `shift` is greater than or equal to the
/// bit size of `T`.
///
/// Safe versions of this intrinsic are available on the integer primitives
/// via the `funnel_shl` method. For example, [`u32::funnel_shl`].
#[rustc_intrinsic]
#[rustc_nounwind]
#[rustc_const_unstable(feature = "funnel_shifts", issue = "145686")]
#[unstable(feature = "funnel_shifts", issue = "145686")]
#[track_caller]
#[miri::intrinsic_fallback_is_spec]
#[ferrocene::annotation(
    "All calls to this function are replaced during code generation unless the target doesn't have this intrinsic. In the latter case, the body of this function remains unchanged, meaning that it calls `intrinsics::fallback::FunnelShift::unchecked_funnel_shl` which is thoroughly tested. The correctness of the code generation is tested in `tests/codegen-llvm/intrinsics/rotate_left.rs`"
)]
#[ferrocene::prevalidated]
pub const unsafe fn unchecked_funnel_shl<T: [const] fallback::FunnelShift>(
    a: T,
    b: T,
    shift: u32,
) -> T {
    // SAFETY: caller ensures that `shift` is in-range
    unsafe { a.unchecked_funnel_shl(b, shift) }
}

/// Funnel Shift right.
///
/// Concatenates `a` and `b` (with `a` in the most significant half),
/// creating an integer twice as wide. Then shift this integer right
/// by `shift` (taken modulo the bit size of `T`), and extract the
/// least significant half. If `a` and `b` are the same, this is equivalent
/// to a rotate right operation.
///
/// It is undefined behavior if `shift` is greater than or equal to the
/// bit size of `T`.
///
/// Safer versions of this intrinsic are available on the integer primitives
/// via the `funnel_shr` method. For example, [`u32::funnel_shr`]
#[rustc_intrinsic]
#[rustc_nounwind]
#[rustc_const_unstable(feature = "funnel_shifts", issue = "145686")]
#[unstable(feature = "funnel_shifts", issue = "145686")]
#[track_caller]
#[miri::intrinsic_fallback_is_spec]
#[ferrocene::annotation(
    "All calls to this function are replaced during code generation unless the target doesn't have this intrinsic. In the latter case, the body of this function remains unchanged, meaning that it calls `intrinsics::fallback::FunnelShift::unchecked_funnel_shr` which is thoroughly tested. "
)]
#[ferrocene::prevalidated]
pub const unsafe fn unchecked_funnel_shr<T: [const] fallback::FunnelShift>(
    a: T,
    b: T,
    shift: u32,
) -> T {
    // SAFETY: caller ensures that `shift` is in-range
    unsafe { a.unchecked_funnel_shr(b, shift) }
}

/// Carryless multiply.
///
/// Safe versions of this intrinsic are available on the integer primitives
/// via the `carryless_mul` method. For example, [`u32::carryless_mul`].
#[rustc_intrinsic]
#[rustc_nounwind]
#[rustc_const_unstable(feature = "uint_carryless_mul", issue = "152080")]
#[unstable(feature = "uint_carryless_mul", issue = "152080")]
#[miri::intrinsic_fallback_is_spec]
#[ferrocene::annotation(
    "All calls to this function are replaced during code generation unless the target doesn't have this intrinsic. In the latter case, the body of this function remains unchanged, meaning that it calls `intrinsics::fallback::CarryingMul::carryless_mul` which is thoroughly tested. "
)]
#[ferrocene::prevalidated]
pub const fn carryless_mul<T: [const] fallback::CarrylessMul>(a: T, b: T) -> T {
    a.carryless_mul(b)
}

/// This is an implementation detail of [`crate::ptr::read`] and should
/// not be used anywhere else.  See its comments for why this exists.
///
/// This intrinsic can *only* be called where the pointer is a local without
/// projections (`read_via_copy(ptr)`, not `read_via_copy(*ptr)`) so that it
/// trivially obeys runtime-MIR rules about derefs in operands.
#[rustc_intrinsic_const_stable_indirect]
#[rustc_nounwind]
#[rustc_intrinsic]
pub const unsafe fn read_via_copy<T>(ptr: *const T) -> T;

/// This is an implementation detail of [`crate::ptr::write`] and should
/// not be used anywhere else.  See its comments for why this exists.
///
/// This intrinsic can *only* be called where the pointer is a local without
/// projections (`write_via_move(ptr, x)`, not `write_via_move(*ptr, x)`) so
/// that it trivially obeys runtime-MIR rules about derefs in operands.
#[rustc_intrinsic_const_stable_indirect]
#[rustc_nounwind]
#[rustc_intrinsic]
pub const unsafe fn write_via_move<T>(ptr: *mut T, value: T);

/// Returns the value of the discriminant for the variant in 'v';
/// if `T` has no discriminant, returns `0`.
///
/// Note that, unlike most intrinsics, this is safe to call;
/// it does not require an `unsafe` block.
/// Therefore, implementations must not require the user to uphold
/// any safety invariants.
///
/// The stabilized version of this intrinsic is [`core::mem::discriminant`].
#[rustc_intrinsic_const_stable_indirect]
#[rustc_nounwind]
#[rustc_intrinsic]
pub const fn discriminant_value<T>(v: &T) -> <T as DiscriminantKind>::Discriminant;

/// Rust's "try catch" construct for unwinding. Invokes the function pointer `try_fn` with the
/// data pointer `data`, and calls `catch_fn` if unwinding occurs while `try_fn` runs.
/// Returns `true` if unwinding occurred and `catch_fn` was called; returns `false` otherwise.
///
/// `catch_fn` must not unwind.
///
/// The third argument is a function called if an unwind occurs (both Rust `panic` and foreign
/// unwinds). This function takes the data pointer and a pointer to the target- and
/// runtime-specific exception object that was caught.
///
/// Note that in the case of a foreign unwinding operation, the exception object data may not be
/// safely usable from Rust, and should not be directly exposed via the standard library. To
/// prevent unsafe access, the library implementation may either abort the process or present an
/// opaque error type to the user.
///
/// For more information, see the compiler's source, as well as the documentation for the stable
/// version of this intrinsic, `std::panic::catch_unwind`.
#[rustc_intrinsic]
#[rustc_nounwind]
pub unsafe fn catch_unwind<Data: ptr::Thin>(
    _try_fn: unsafe fn(*mut Data),
    _data: *mut Data,
    _catch_fn: unsafe fn(*mut Data, *mut u8),
) -> bool;

/// Emits a `nontemporal` store, which gives a hint to the CPU that the data should not be held
/// in cache. Except for performance, this is fully equivalent to `ptr.write(val)`.
///
/// Not all architectures provide such an operation. For instance, x86 does not: while `MOVNT`
/// exists, that operation is *not* equivalent to `ptr.write(val)` (`MOVNT` writes can be reordered
/// in ways that are not allowed for regular writes).
#[rustc_intrinsic]
#[rustc_nounwind]
pub unsafe fn nontemporal_store<T>(ptr: *mut T, val: T);

/// See documentation of `<*const T>::offset_from` for details.
#[rustc_intrinsic_const_stable_indirect]
#[rustc_nounwind]
#[rustc_intrinsic]
pub const unsafe fn ptr_offset_from<T>(ptr: *const T, base: *const T) -> isize;

/// See documentation of `<*const T>::offset_from_unsigned` for details.
#[rustc_nounwind]
#[rustc_intrinsic]
#[rustc_intrinsic_const_stable_indirect]
pub const unsafe fn ptr_offset_from_unsigned<T>(ptr: *const T, base: *const T) -> usize;

/// See documentation of `<*const T>::guaranteed_eq` for details.
/// Returns `2` if the result is unknown.
/// Returns `1` if the pointers are guaranteed equal.
/// Returns `0` if the pointers are guaranteed inequal.
#[rustc_intrinsic]
#[rustc_nounwind]
#[rustc_do_not_const_check]
#[inline]
#[miri::intrinsic_fallback_is_spec]
#[ferrocene::prevalidated]
pub const fn ptr_guaranteed_cmp<T>(ptr: *const T, other: *const T) -> u8 {
    (ptr == other) as u8
}

/// Determines whether the raw bytes of the two values are equal.
///
/// This is particularly handy for arrays, since it allows things like just
/// comparing `i96`s instead of forcing `alloca`s for `[6 x i16]`.
///
/// Above some backend-decided threshold this will emit calls to `memcmp`,
/// like slice equality does, instead of causing massive code size.
///
/// Since this works by comparing the underlying bytes, the actual `T` is
/// not particularly important.  It will be used for its size and alignment,
/// but any validity restrictions will be ignored, not enforced.
///
/// # Safety
///
/// It's UB to call this if any of the *bytes* in `*a` or `*b` are uninitialized.
/// Note that this is a stricter criterion than just the *values* being
/// fully-initialized: if `T` has padding, it's UB to call this intrinsic.
///
/// At compile-time, it is furthermore UB to call this if any of the bytes
/// in `*a` or `*b` have provenance.
///
/// (The implementation is allowed to branch on the results of comparisons,
/// which is UB if any of their inputs are `undef`.)
#[rustc_nounwind]
#[rustc_intrinsic]
pub const unsafe fn raw_eq<T>(a: &T, b: &T) -> bool;

/// Lexicographically compare `[left, left + bytes)` and `[right, right + bytes)`
/// as unsigned bytes, returning negative if `left` is less, zero if all the
/// bytes match, or positive if `left` is greater.
///
/// This underlies things like `<[u8]>::cmp`, and will usually lower to `memcmp`.
///
/// # Safety
///
/// `left` and `right` must each be [valid] for reads of `bytes` bytes.
///
/// Note that this applies to the whole range, not just until the first byte
/// that differs.  That allows optimizations that can read in large chunks.
///
/// [valid]: crate::ptr#safety
#[rustc_nounwind]
#[rustc_intrinsic]
#[rustc_const_unstable(feature = "const_cmp", issue = "143800")]
pub const unsafe fn compare_bytes(left: *const u8, right: *const u8, bytes: usize) -> i32;

/// See documentation of [`std::hint::black_box`] for details.
///
/// [`std::hint::black_box`]: crate::hint::black_box
#[rustc_nounwind]
#[rustc_intrinsic]
#[rustc_intrinsic_const_stable_indirect]
pub const fn black_box<T>(dummy: T) -> T;

/// Selects which function to call depending on the context.
///
/// If this function is evaluated at compile-time, then a call to this
/// intrinsic will be replaced with a call to `called_in_const`. It gets
/// replaced with a call to `called_at_rt` otherwise.
///
/// This function is safe to call, but note the stability concerns below.
///
/// # Type Requirements
///
/// The two functions must be both function items. They cannot be function
/// pointers or closures. The first function must be a `const fn`.
///
/// `arg` will be the tupled arguments that will be passed to either one of
/// the two functions, therefore, both functions must accept the same type of
/// arguments. Both functions must return RET.
///
/// # Stability concerns
///
/// Rust has not yet decided that `const fn` are allowed to tell whether
/// they run at compile-time or at runtime. Therefore, when using this
/// intrinsic anywhere that can be reached from stable, it is crucial that
/// the end-to-end behavior of the stable `const fn` is the same for both
/// modes of execution. (Here, Undefined Behavior is considered "the same"
/// as any other behavior, so if the function exhibits UB at runtime then
/// it may do whatever it wants at compile-time.)
///
/// Here is an example of how this could cause a problem:
/// ```no_run
/// #![feature(const_eval_select)]
/// #![feature(core_intrinsics)]
/// # #![allow(internal_features)]
/// use std::intrinsics::const_eval_select;
///
/// // Standard library
/// pub const fn inconsistent() -> i32 {
///     fn runtime() -> i32 { 1 }
///     const fn compiletime() -> i32 { 2 }
///
///     // ⚠ This code violates the required equivalence of `compiletime`
///     // and `runtime`.
///     const_eval_select((), compiletime, runtime)
/// }
///
/// // User Crate
/// const X: i32 = inconsistent();
/// let x = inconsistent();
/// assert_eq!(x, X);
/// ```
///
/// Currently such an assertion would always succeed; until Rust decides
/// otherwise, that principle should not be violated.
#[rustc_const_unstable(feature = "const_eval_select", issue = "124625")]
#[rustc_intrinsic]
pub const fn const_eval_select<ARG: Tuple, F, G, RET>(
    _arg: ARG,
    _called_in_const: F,
    _called_at_rt: G,
) -> RET
where
    G: FnOnce<ARG, Output = RET>,
    F: const FnOnce<ARG, Output = RET>;

/// A macro to make it easier to invoke const_eval_select. Use as follows:
/// ```rust,ignore (just a macro example)
/// const_eval_select!(
///     @capture { arg1: i32 = some_expr, arg2: T = other_expr } -> U:
///     if const #[attributes_for_const_arm] {
///         // Compile-time code goes here.
///     } else #[attributes_for_runtime_arm] {
///         // Run-time code goes here.
///     }
/// )
/// ```
/// The `@capture` block declares which surrounding variables / expressions can be
/// used inside the `if const`.
/// Note that the two arms of this `if` really each become their own function, which is why the
/// macro supports setting attributes for those functions. Both functions are marked as `#[inline]`.
///
/// See [`const_eval_select()`] for the rules and requirements around that intrinsic.
pub(crate) macro const_eval_select {
    (
        @capture$([$($binders:tt)*])? { $($arg:ident : $ty:ty = $val:expr),* $(,)? } $( -> $ret:ty )? :
        if const
            $(#[$compiletime_attr:meta])* $compiletime:block
        else
            $(#[$runtime_attr:meta])* $runtime:block
    ) => {{
        #[inline]
        $(#[$runtime_attr])*
        #[ferrocene::prevalidated]
        fn runtime$(<$($binders)*>)?($($arg: $ty),*) $( -> $ret )? {
            $runtime
        }

        #[inline]
        $(#[$compiletime_attr])*
        #[ferrocene::annotation("Cannot be covered as this only runs during compilation.")]
        #[ferrocene::prevalidated]
        const fn compiletime$(<$($binders)*>)?($($arg: $ty),*) $( -> $ret )? {
            // Don't warn if one of the arguments is unused.
            $(let _ = $arg;)*

            $compiletime
        }

        const_eval_select(($($val,)*), compiletime, runtime)
    }},
    // We support leaving away the `val` expressions for *all* arguments
    // (but not for *some* arguments, that's too tricky).
    (
        @capture$([$($binders:tt)*])? { $($arg:ident : $ty:ty),* $(,)? } $( -> $ret:ty )? :
        if const
            $(#[$compiletime_attr:meta])* $compiletime:block
        else
            $(#[$runtime_attr:meta])* $runtime:block
    ) => {
        $crate::intrinsics::const_eval_select!(
            @capture$([$($binders)*])? { $($arg : $ty = $arg),* } $(-> $ret)? :
            if const
                $(#[$compiletime_attr])* $compiletime
            else
                $(#[$runtime_attr])* $runtime
        )
    },
}

/// Returns whether the argument's value is statically known at
/// compile-time.
///
/// This is useful when there is a way of writing the code that will
/// be *faster* when some variables have known values, but *slower*
/// in the general case: an `if is_val_statically_known(var)` can be used
/// to select between these two variants. The `if` will be optimized away
/// and only the desired branch remains.
///
/// Formally speaking, this function non-deterministically returns `true`
/// or `false`, and the caller has to ensure sound behavior for both cases.
/// In other words, the following code has *Undefined Behavior*:
///
/// ```no_run
/// #![feature(core_intrinsics)]
/// # #![allow(internal_features)]
/// use std::hint::unreachable_unchecked;
/// use std::intrinsics::is_val_statically_known;
///
/// if !is_val_statically_known(0) { unsafe { unreachable_unchecked(); } }
/// ```
///
/// This also means that the following code's behavior is unspecified; it
/// may panic, or it may not:
///
/// ```no_run
/// #![feature(core_intrinsics)]
/// # #![allow(internal_features)]
/// use std::intrinsics::is_val_statically_known;
///
/// assert_eq!(is_val_statically_known(0), is_val_statically_known(0));
/// ```
///
/// Unsafe code may not rely on `is_val_statically_known` returning any
/// particular value, ever. However, the compiler will generally make it
/// return `true` only if the value of the argument is actually known.
///
/// # Type Requirements
///
/// `T` must be either a `bool`, a `char`, a primitive numeric type (e.g. `f32`,
/// but not `NonZeroISize`), or any thin pointer (e.g. `*mut String`).
/// Any other argument types *may* cause a compiler error.
///
/// ## Pointers
///
/// When the input is a pointer, only the pointer itself is
/// ever considered. The pointee has no effect. Currently, these functions
/// behave identically:
///
/// ```
/// #![feature(core_intrinsics)]
/// # #![allow(internal_features)]
/// use std::intrinsics::is_val_statically_known;
///
/// fn foo(x: &i32) -> bool {
///     is_val_statically_known(x)
/// }
///
/// fn bar(x: &i32) -> bool {
///     is_val_statically_known(
///         (x as *const i32).addr()
///     )
/// }
/// # _ = foo(&5_i32);
/// # _ = bar(&5_i32);
/// ```
#[ferrocene::annotation(
    "All calls of this function are replaced during code generation, meaning that the code inside the function is never run. The correctness of the code generation is tested in `tests/codegen-llvm/is_val_statically_known.rs`"
)]
#[rustc_const_stable_indirect]
#[rustc_nounwind]
#[unstable(feature = "core_intrinsics", issue = "none")]
#[rustc_intrinsic]
#[ferrocene::prevalidated]
pub const fn is_val_statically_known<T: Copy>(_arg: T) -> bool {
    false
}

/// Non-overlapping *typed* swap of a single value.
///
/// The codegen backends will replace this with a better implementation when
/// `T` is a simple type that can be loaded and stored as an immediate.
///
/// The stabilized form of this intrinsic is [`crate::mem::swap`].
///
/// # Safety
/// Behavior is undefined if any of the following conditions are violated:
///
/// * Both `x` and `y` must be [valid] for both reads and writes.
///
/// * Both `x` and `y` must be properly aligned.
///
/// * The region of memory beginning at `x` must *not* overlap with the region of memory
///   beginning at `y`.
///
/// * The memory pointed by `x` and `y` must both contain values of type `T`.
///
/// [valid]: crate::ptr#safety
#[rustc_nounwind]
#[inline]
#[rustc_intrinsic]
#[rustc_intrinsic_const_stable_indirect]
#[ferrocene::prevalidated]
pub const unsafe fn typed_swap_nonoverlapping<T>(x: *mut T, y: *mut T) {
    // SAFETY: The caller provided single non-overlapping items behind
    // pointers, so swapping them with `count: 1` is fine.
    unsafe { ptr::swap_nonoverlapping(x, y, 1) };
}

/// Returns whether we should perform some UB-checking at runtime. This eventually evaluates to
/// `cfg!(ub_checks)`, but behaves different from `cfg!` when mixing crates built with different
/// flags: if the crate has UB checks enabled or carries the `#[rustc_preserve_ub_checks]`
/// attribute, evaluation is delayed until monomorphization (or until the call gets inlined into
/// a crate that does not delay evaluation further); otherwise it can happen any time.
///
/// The common case here is a user program built with ub_checks linked against the distributed
/// sysroot which is built without ub_checks but with `#[rustc_preserve_ub_checks]`.
/// For code that gets monomorphized in the user crate (i.e., generic functions and functions with
/// `#[inline]`), gating assertions on `ub_checks()` rather than `cfg!(ub_checks)` means that
/// assertions are enabled whenever the *user crate* has UB checks enabled. However, if the
/// user has UB checks disabled, the checks will still get optimized out. This intrinsic is
/// primarily used by [`crate::ub_checks::assert_unsafe_precondition`].
///
/// # Consteval
///
/// In consteval, this function currently returns `true`. This is because the value of the `ub_checks`
/// configuration can differ across crates, but we need this function to always return the same
/// value in consteval in order to avoid unsoundness.
#[rustc_intrinsic_const_stable_indirect] // just for UB checks
#[inline(always)]
#[rustc_intrinsic]
#[ferrocene::annotation(
    "This function is always used in `assert_unsafe_precondition` which produces an unwinding panic, meaning that we cannot cover it."
)]
#[ferrocene::prevalidated]
pub const fn ub_checks() -> bool {
    cfg!(ub_checks)
}

/// Returns whether we should perform some overflow-checking at runtime. This eventually evaluates to
/// `cfg!(overflow_checks)`, but behaves different from `cfg!` when mixing crates built with different
/// flags: if the crate has overflow checks enabled or carries the `#[rustc_inherit_overflow_checks]`
/// attribute, evaluation is delayed until monomorphization (or until the call gets inlined into
/// a crate that does not delay evaluation further); otherwise it can happen any time.
///
/// The common case here is a user program built with overflow_checks linked against the distributed
/// sysroot which is built without overflow_checks but with `#[rustc_inherit_overflow_checks]`.
/// For code that gets monomorphized in the user crate (i.e., generic functions and functions with
/// `#[inline]`), gating assertions on `overflow_checks()` rather than `cfg!(overflow_checks)` means that
/// assertions are enabled whenever the *user crate* has overflow checks enabled. However if the
/// user has overflow checks disabled, the checks will still get optimized out.
///
/// # Consteval
///
/// In consteval, this function currently returns `true`. This is because the value of the `overflow_checks`
/// configuration can differ across crates, but we need this function to always return the same
/// value in consteval in order to avoid unsoundness.
#[inline(always)]
#[rustc_intrinsic]
#[ferrocene::annotation(
    "This function cannot trivially be tested since it depends on the build configuration. It was manually reviewed."
)]
#[ferrocene::prevalidated]
pub const fn overflow_checks() -> bool {
    cfg!(debug_assertions)
}

/// Allocates a block of memory at compile time.
/// At runtime, just returns a null pointer.
///
/// # Safety
///
/// - The `align` argument must be a power of two.
///    - At compile time, a compile error occurs if this constraint is violated.
///    - At runtime, it is not checked.
#[rustc_const_unstable(feature = "const_heap", issue = "79597")]
#[rustc_nounwind]
#[rustc_intrinsic]
#[miri::intrinsic_fallback_is_spec]
pub const unsafe fn const_allocate(_size: usize, _align: usize) -> *mut u8 {
    // const eval overrides this function, but runtime code for now just returns null pointers.
    // See <https://github.com/rust-lang/rust/issues/93935>.
    crate::ptr::null_mut()
}

/// Deallocates a memory which allocated by `intrinsics::const_allocate` at compile time.
/// At runtime, it does nothing.
///
/// # Safety
///
/// - The `align` argument must be a power of two.
///    - At compile time, a compile error occurs if this constraint is violated.
///    - At runtime, it is not checked.
/// - If the `ptr` is created in an another const, this intrinsic doesn't deallocate it.
/// - If the `ptr` is pointing to a local variable, this intrinsic doesn't deallocate it.
#[rustc_const_unstable(feature = "const_heap", issue = "79597")]
#[unstable(feature = "core_intrinsics", issue = "none")]
#[rustc_nounwind]
#[rustc_intrinsic]
#[miri::intrinsic_fallback_is_spec]
pub const unsafe fn const_deallocate(_ptr: *mut u8, _size: usize, _align: usize) {
    // Runtime NOP
}

/// Convert the allocation this pointer points to into immutable global memory.
/// The pointer must point to the beginning of a heap allocation.
/// This operation only makes sense during compile time. At runtime, it does nothing.
#[rustc_const_unstable(feature = "const_heap", issue = "79597")]
#[rustc_nounwind]
#[rustc_intrinsic]
#[miri::intrinsic_fallback_is_spec]
#[ferrocene::annotation("This function is also a noop in runtime so we can't cover it currently.")]
#[ferrocene::prevalidated]
pub const unsafe fn const_make_global(ptr: *mut u8) -> *const u8 {
    // const eval overrides this function; at runtime, it is a NOP.
    ptr
}

/// Check if the pre-condition `cond` has been met.
///
/// By default, if `contract_checks` is enabled, this will panic with no unwind if the condition
/// returns false.
///
/// Note that this function is a no-op during constant evaluation.
#[unstable(feature = "contracts_internals", issue = "128044")]
// Calls to this function get inserted by an AST expansion pass, which uses the equivalent of
// `#[allow_internal_unstable]` to allow using `contracts_internals` functions. Const-checking
// doesn't honor `#[allow_internal_unstable]`, so for the const feature gate we use the user-facing
// `contracts` feature rather than the perma-unstable `contracts_internals`
#[rustc_const_unstable(feature = "contracts", issue = "128044")]
#[lang = "contract_check_requires"]
#[rustc_intrinsic]
pub const fn contract_check_requires<C: Fn() -> bool + Copy>(cond: C) {
    const_eval_select!(
        @capture[C: Fn() -> bool + Copy] { cond: C } :
        if const {
                // Do nothing
        } else {
            if !cond() {
                // Emit no unwind panic in case this was a safety requirement.
                crate::panicking::panic_nounwind("failed requires check");
            }
        }
    )
}

/// Check if the post-condition `cond` has been met.
///
/// By default, if `contract_checks` is enabled, this will panic with no unwind if the condition
/// returns false.
///
/// If `cond` is `None`, then no postcondition checking is performed.
///
/// Note that this function is a no-op during constant evaluation.
#[unstable(feature = "contracts_internals", issue = "128044")]
// Similar to `contract_check_requires`, we need to use the user-facing
// `contracts` feature rather than the perma-unstable `contracts_internals`.
// Const-checking doesn't honor allow_internal_unstable logic used by contract expansion.
#[rustc_const_unstable(feature = "contracts", issue = "128044")]
#[lang = "contract_check_ensures"]
#[rustc_intrinsic]
pub const fn contract_check_ensures<C: Fn(&Ret) -> bool + Copy, Ret>(
    cond: Option<C>,
    ret: Ret,
) -> Ret {
    const_eval_select!(
        @capture[C: Fn(&Ret) -> bool + Copy, Ret] { cond: Option<C>, ret: Ret } -> Ret :
        if const {
            // Do nothing
            ret
        } else {
            match cond {
                crate::option::Option::Some(cond) => {
                    if !cond(&ret) {
                        // Emit no unwind panic in case this was a safety requirement.
                        crate::panicking::panic_nounwind("failed ensures check");
                    }
                },
                crate::option::Option::None => {},
            }
            ret
        }
    )
}

/// The intrinsic will return the size stored in that vtable.
///
/// # Safety
///
/// `ptr` must point to a vtable.
#[rustc_nounwind]
#[unstable(feature = "core_intrinsics", issue = "none")]
#[rustc_intrinsic]
pub unsafe fn vtable_size(ptr: *const ()) -> usize;

/// The intrinsic will return the alignment stored in that vtable.
///
/// # Safety
///
/// `ptr` must point to a vtable.
#[rustc_nounwind]
#[unstable(feature = "core_intrinsics", issue = "none")]
#[rustc_intrinsic]
pub unsafe fn vtable_align(ptr: *const ()) -> usize;

/// The size of a type in bytes.
///
/// Note that, unlike most intrinsics, this is safe to call;
/// it does not require an `unsafe` block.
/// Therefore, implementations must not require the user to uphold
/// any safety invariants.
///
/// More specifically, this is the offset in bytes between successive
/// items of the same type, including alignment padding.
///
/// Note that, unlike most intrinsics, this can only be called at compile-time
/// as backends do not have an implementation for it. The only caller (its
/// stable counterpart) wraps this intrinsic call in a `const` block so that
/// backends only see an evaluated constant.
///
/// The stabilized version of this intrinsic is [`core::mem::size_of`].
#[rustc_nounwind]
#[unstable(feature = "core_intrinsics", issue = "none")]
#[rustc_intrinsic_const_stable_indirect]
#[rustc_intrinsic]
pub const fn size_of<T>() -> usize;

/// The minimum alignment of a type.
///
/// Note that, unlike most intrinsics, this is safe to call;
/// it does not require an `unsafe` block.
/// Therefore, implementations must not require the user to uphold
/// any safety invariants.
///
/// Note that, unlike most intrinsics, this can only be called at compile-time
/// as backends do not have an implementation for it. The only caller (its
/// stable counterpart) wraps this intrinsic call in a `const` block so that
/// backends only see an evaluated constant.
///
/// The stabilized version of this intrinsic is [`core::mem::align_of`].
#[rustc_nounwind]
#[unstable(feature = "core_intrinsics", issue = "none")]
#[rustc_intrinsic_const_stable_indirect]
#[rustc_intrinsic]
pub const fn align_of<T>() -> usize;

/// The offset of a field inside a type.
///
/// Note that, unlike most intrinsics, this is safe to call;
/// it does not require an `unsafe` block.
/// Therefore, implementations must not require the user to uphold
/// any safety invariants.
///
/// This intrinsic can only be evaluated at compile-time, and should only appear in
/// constants or inline const blocks.
///
/// The stabilized version of this intrinsic is [`core::mem::offset_of`].
/// This intrinsic is also a lang item so `offset_of!` can desugar to calls to it.
#[rustc_nounwind]
#[unstable(feature = "core_intrinsics", issue = "none")]
#[rustc_const_unstable(feature = "core_intrinsics", issue = "none")]
#[rustc_intrinsic_const_stable_indirect]
#[rustc_intrinsic]
#[lang = "offset_of"]
pub const fn offset_of<T: PointeeSized>(variant: u32, field: u32) -> usize;

/// The offset of a field queried by its field representing type.
///
/// Returns the offset of the field represented by `F`. This function essentially does the same as
/// the [`offset_of`] intrinsic, but expects the field to be represented by a generic rather than
/// the variant and field indices. This also is a safe intrinsic and can only be evaluated at
/// compile-time, so it should only appear in constants or inline const blocks.
///
/// There should be no need to call this intrinsic manually, as its value is used to define
/// [`Field::OFFSET`](crate::field::Field::OFFSET), which is publicly accessible.
#[rustc_intrinsic]
#[unstable(feature = "field_projections", issue = "145383")]
#[rustc_const_unstable(feature = "field_projections", issue = "145383")]
pub const fn field_offset<F: crate::field::Field>() -> usize;

/// Returns the number of variants of the type `T` cast to a `usize`;
/// if `T` has no variants, returns `0`. Uninhabited variants will be counted.
///
/// Note that, unlike most intrinsics, this can only be called at compile-time
/// as backends do not have an implementation for it. The only caller (its
/// stable counterpart) wraps this intrinsic call in a `const` block so that
/// backends only see an evaluated constant.
///
/// The to-be-stabilized version of this intrinsic is [`crate::mem::variant_count`].
#[rustc_nounwind]
#[unstable(feature = "core_intrinsics", issue = "none")]
#[rustc_intrinsic]
pub const fn variant_count<T>() -> usize;

/// The size of the referenced value in bytes.
///
/// The stabilized version of this intrinsic is [`core::mem::size_of_val`].
///
/// # Safety
///
/// See [`crate::mem::size_of_val_raw`] for safety conditions.
#[rustc_nounwind]
#[unstable(feature = "core_intrinsics", issue = "none")]
#[rustc_intrinsic]
#[rustc_intrinsic_const_stable_indirect]
pub const unsafe fn size_of_val<T: ?Sized>(ptr: *const T) -> usize;

/// The required alignment of the referenced value.
///
/// The stabilized version of this intrinsic is [`core::mem::align_of_val`].
///
/// # Safety
///
/// See [`crate::mem::align_of_val_raw`] for safety conditions.
#[rustc_nounwind]
#[unstable(feature = "core_intrinsics", issue = "none")]
#[rustc_intrinsic]
#[rustc_intrinsic_const_stable_indirect]
pub const unsafe fn align_of_val<T: ?Sized>(ptr: *const T) -> usize;

#[rustc_intrinsic]
#[rustc_comptime]
#[unstable(feature = "core_intrinsics", issue = "none")]
/// Check if a type represented by a `TypeId` implements a trait represented by a `TypeId`.
/// It can only be called at compile time, the backends do
/// not implement it. If it implements the trait the dyn metadata gets returned for vtable access.
pub fn type_id_vtable(
    _id: crate::any::TypeId,
    _trait: crate::any::TypeId,
) -> Option<ptr::DynMetadata<*const ()>> {
    panic!(
        "`TypeId::trait_info_of` and `trait_info_of_trait_type_id` can only be called at compile-time"
    )
}

/// Compute the type information of a concrete type.
/// It can only be called at compile time, the backends do
/// not implement it.
#[rustc_intrinsic]
#[unstable(feature = "core_intrinsics", issue = "none")]
pub const fn type_of(_id: crate::any::TypeId) -> crate::mem::type_info::Type {
    panic!("`TypeId::info` can only be called at compile-time")
}

/// Gets a static string slice containing the name of a type.
///
/// Note that, unlike most intrinsics, this can only be called at compile-time
/// as backends do not have an implementation for it. The only caller (its
/// stable counterpart) wraps this intrinsic call in a `const` block so that
/// backends only see an evaluated constant.
///
/// The stabilized version of this intrinsic is [`core::any::type_name`].
#[rustc_nounwind]
#[unstable(feature = "core_intrinsics", issue = "none")]
#[rustc_intrinsic]
pub const fn type_name<T: ?Sized>() -> &'static str;

/// Gets an identifier which is globally unique to the specified type. This
/// function will return the same value for a type regardless of whichever
/// crate it is invoked in.
///
/// Note that, unlike most intrinsics, this can only be called at compile-time
/// as backends do not have an implementation for it. The only caller (its
/// stable counterpart) wraps this intrinsic call in a `const` block so that
/// backends only see an evaluated constant.
///
/// The stabilized version of this intrinsic is [`core::any::TypeId::of`].
#[rustc_nounwind]
#[unstable(feature = "core_intrinsics", issue = "none")]
#[rustc_intrinsic]
#[rustc_comptime]
pub fn type_id<T: ?Sized>() -> crate::any::TypeId;

/// Tests (at compile-time) if two [`crate::any::TypeId`] instances identify the
/// same type. This is necessary because at const-eval time the actual discriminating
/// data is opaque and cannot be inspected directly.
///
/// The stabilized version of this intrinsic is the [PartialEq] impl for [`core::any::TypeId`].
#[rustc_nounwind]
#[unstable(feature = "core_intrinsics", issue = "none")]
#[rustc_intrinsic]
#[rustc_do_not_const_check]
#[ferrocene::prevalidated]
pub const fn type_id_eq(a: crate::any::TypeId, b: crate::any::TypeId) -> bool {
    // SAFETY: we know `TypeId` is 16 bytes of initialized data.
    // This is runtime-only code so we do not have to worry about provenance.
    unsafe { crate::mem::transmute::<_, u128>(a) == crate::mem::transmute::<_, u128>(b) }
}

/// Gets the size of the type represented by this `TypeId`.
///
/// The more user-friendly version of this intrinsic is [`core::any::TypeId::size`].
#[rustc_intrinsic]
#[unstable(feature = "core_intrinsics", issue = "none")]
#[rustc_comptime]
pub fn size_of_type_id(_id: crate::any::TypeId) -> Option<usize> {
    panic!("`TypeId::size` can only be called at compile-time")
}

/// Gets the number of variants of the type represented by this `TypeId`.
///
/// The more user-friendly version of this intrinsic is [`core::any::TypeId::variants`].
#[rustc_intrinsic]
#[unstable(feature = "core_intrinsics", issue = "none")]
#[rustc_comptime]
pub fn type_id_variants(_id: crate::any::TypeId) -> usize {
    panic!("`TypeId::variants` can only be called at compile-time")
}

/// Gets the number of fields at the given `variant_index` represented by this `TypeId`.
///
/// The more user-friendly version of this intrinsic is [`core::any::TypeId::fields`].
#[rustc_intrinsic]
#[unstable(feature = "core_intrinsics", issue = "none")]
#[rustc_comptime]
pub fn type_id_fields(_id: crate::any::TypeId, _variant_index: usize) -> usize {
    panic!("`TypeId::fields` can only be called at compile-time")
}

/// Gets the [`FieldRepresentingType`]'s `TypeId` at the given index of the type represented by this `TypeId`.
///
/// The more user-friendly version of this intrinsic is [`core::any::TypeId::field`].
///
/// [`FieldRepresentingType`]: crate::field::FieldRepresentingType
#[rustc_intrinsic]
#[unstable(feature = "core_intrinsics", issue = "none")]
#[rustc_comptime]
pub fn type_id_field_representing_type(
    _id: crate::any::TypeId,
    _variant_index: usize,
    _field_index: usize,
) -> crate::any::TypeId {
    panic!("`TypeId::field` can only be called at compile-time")
}

/// Gets the actual field `TypeId` of the [`FieldRepresentingType`]'s `TypeId`.
///
/// The more user-friendly version of this intrinsic is [`core::mem::type_info::FieldId::type_id`].
///
/// [`FieldRepresentingType`]: crate::field::FieldRepresentingType
#[rustc_intrinsic]
#[unstable(feature = "core_intrinsics", issue = "none")]
#[rustc_comptime]
pub fn field_representing_type_actual_type_id(
    _frt_type_id: crate::any::TypeId,
) -> crate::any::TypeId {
    panic!("`FieldId::type_id` can only be called at compile-time")
}

/// Lowers in MIR to `Rvalue::Aggregate` with `AggregateKind::RawPtr`.
///
/// This is used to implement functions like `slice::from_raw_parts_mut` and
/// `ptr::from_raw_parts` in a way compatible with the compiler being able to
/// change the possible layouts of pointers.
#[rustc_nounwind]
#[unstable(feature = "core_intrinsics", issue = "none")]
#[rustc_intrinsic_const_stable_indirect]
#[rustc_intrinsic]
pub const fn aggregate_raw_ptr<P: bounds::BuiltinDeref, D, M>(data: D, meta: M) -> P
where
    <P as bounds::BuiltinDeref>::Pointee: ptr::Pointee<Metadata = M>;

/// Lowers in MIR to `Rvalue::UnaryOp` with `UnOp::PtrMetadata`.
///
/// This is used to implement functions like `ptr::metadata`.
#[rustc_nounwind]
#[unstable(feature = "core_intrinsics", issue = "none")]
#[rustc_intrinsic_const_stable_indirect]
#[rustc_intrinsic]
pub const fn ptr_metadata<P: ptr::Pointee<Metadata = M> + PointeeSized, M>(ptr: *const P) -> M;

/// This is an accidentally-stable alias to [`ptr::copy_nonoverlapping`]; use that instead.
// Note (intentionally not in the doc comment): `ptr::copy_nonoverlapping` adds some extra
// debug assertions; if you are writing compiler tests or code inside the standard library
// that wants to avoid those debug assertions, directly call this intrinsic instead.
#[stable(feature = "rust1", since = "1.0.0")]
#[rustc_allowed_through_unstable_modules = "import this function via `std::ptr` instead"]
#[rustc_const_stable(feature = "const_intrinsic_copy", since = "1.83.0")]
#[rustc_nounwind]
#[rustc_intrinsic]
pub const unsafe fn copy_nonoverlapping<T>(src: *const T, dst: *mut T, count: usize);

/// This is an accidentally-stable alias to [`ptr::copy`]; use that instead.
// Note (intentionally not in the doc comment): `ptr::copy` adds some extra
// debug assertions; if you are writing compiler tests or code inside the standard library
// that wants to avoid those debug assertions, directly call this intrinsic instead.
#[stable(feature = "rust1", since = "1.0.0")]
#[rustc_allowed_through_unstable_modules = "import this function via `std::ptr` instead"]
#[rustc_const_stable(feature = "const_intrinsic_copy", since = "1.83.0")]
#[rustc_nounwind]
#[rustc_intrinsic]
pub const unsafe fn copy<T>(src: *const T, dst: *mut T, count: usize);

/// This is an accidentally-stable alias to [`ptr::write_bytes`]; use that instead.
// Note (intentionally not in the doc comment): `ptr::write_bytes` adds some extra
// debug assertions; if you are writing compiler tests or code inside the standard library
// that wants to avoid those debug assertions, directly call this intrinsic instead.
#[stable(feature = "rust1", since = "1.0.0")]
#[rustc_allowed_through_unstable_modules = "import this function via `std::ptr` instead"]
#[rustc_const_stable(feature = "const_intrinsic_copy", since = "1.83.0")]
#[rustc_nounwind]
#[rustc_intrinsic]
pub const unsafe fn write_bytes<T>(dst: *mut T, val: u8, count: usize);

/// Returns the minimum of two `f16` values, ignoring NaN.
///
/// This behaves like IEEE 754-2019 minimumNumber, *except* that it does not order signed
/// zeros deterministically. In particular:
/// If one of the arguments is NaN (quiet or signaling), then the other argument is returned. If
/// both arguments are NaN, returns NaN. If the inputs compare equal (such as for the case of `+0.0`
/// and `-0.0`), either input may be returned non-deterministically.
///
/// Note that, unlike most intrinsics, this is safe to call;
/// it does not require an `unsafe` block.
/// Therefore, implementations must not require the user to uphold
/// any safety invariants.
///
/// The stabilized version of this intrinsic is [`f16::min`].
#[rustc_nounwind]
#[rustc_intrinsic]
pub const fn minimum_number_nsz_f16(x: f16, y: f16) -> f16 {
    if x.is_nan() || y <= x {
        y
    } else {
        // Either y > x or y is a NaN.
        x
    }
}

/// Returns the minimum of two `f32` values, ignoring NaN.
///
/// This behaves like IEEE 754-2019 minimumNumber, *except* that it does not order signed
/// zeros deterministically. In particular:
/// If one of the arguments is NaN (quiet or signaling), then the other argument is returned. If
/// both arguments are NaN, returns NaN. If the inputs compare equal (such as for the case of `+0.0`
/// and `-0.0`), either input may be returned non-deterministically.
///
/// Note that, unlike most intrinsics, this is safe to call;
/// it does not require an `unsafe` block.
/// Therefore, implementations must not require the user to uphold
/// any safety invariants.
///
/// The stabilized version of this intrinsic is [`f32::min`].
#[rustc_nounwind]
#[rustc_intrinsic_const_stable_indirect]
#[rustc_intrinsic]
#[ferrocene::prevalidated]
pub const fn minimum_number_nsz_f32(x: f32, y: f32) -> f32 {
    if x.is_nan() || y <= x {
        y
    } else {
        // Either y > x or y is a NaN.
        x
    }
}

/// Returns the minimum of two `f64` values, ignoring NaN.
///
/// This behaves like IEEE 754-2019 minimumNumber, *except* that it does not order signed
/// zeros deterministically. In particular:
/// If one of the arguments is NaN (quiet or signaling), then the other argument is returned. If
/// both arguments are NaN, returns NaN. If the inputs compare equal (such as for the case of `+0.0`
/// and `-0.0`), either input may be returned non-deterministically.
///
/// Note that, unlike most intrinsics, this is safe to call;
/// it does not require an `unsafe` block.
/// Therefore, implementations must not require the user to uphold
/// any safety invariants.
///
/// The stabilized version of this intrinsic is [`f64::min`].
#[rustc_nounwind]
#[rustc_intrinsic_const_stable_indirect]
#[rustc_intrinsic]
pub const fn minimum_number_nsz_f64(x: f64, y: f64) -> f64 {
    if x.is_nan() || y <= x {
        y
    } else {
        // Either y > x or y is a NaN.
        x
    }
}

/// Returns the minimum of two `f128` values, ignoring NaN.
///
/// This behaves like IEEE 754-2019 minimumNumber, *except* that it does not order signed
/// zeros deterministically. In particular:
/// If one of the arguments is NaN (quiet or signaling), then the other argument is returned. If
/// both arguments are NaN, returns NaN. If the inputs compare equal (such as for the case of `+0.0`
/// and `-0.0`), either input may be returned non-deterministically.
///
/// Note that, unlike most intrinsics, this is safe to call;
/// it does not require an `unsafe` block.
/// Therefore, implementations must not require the user to uphold
/// any safety invariants.
///
/// The stabilized version of this intrinsic is [`f128::min`].
#[rustc_nounwind]
#[rustc_intrinsic]
pub const fn minimum_number_nsz_f128(x: f128, y: f128) -> f128 {
    if x.is_nan() || y <= x {
        y
    } else {
        // Either y > x or y is a NaN.
        x
    }
}

/// Returns the minimum of two `f16` values, propagating NaN.
///
/// This behaves like IEEE 754-2019 minimum. In particular:
/// If one of the arguments is NaN, then a NaN is returned using the usual NaN propagation rules.
/// For this operation, -0.0 is considered to be strictly less than +0.0.
///
/// Note that, unlike most intrinsics, this is safe to call;
/// it does not require an `unsafe` block.
/// Therefore, implementations must not require the user to uphold
/// any safety invariants.
#[rustc_nounwind]
#[rustc_intrinsic]
pub const fn minimumf16(x: f16, y: f16) -> f16 {
    if x < y {
        x
    } else if y < x {
        y
    } else if x == y {
        if x.is_sign_negative() && y.is_sign_positive() { x } else { y }
    } else {
        // At least one input is NaN. Use `+` to perform NaN propagation and quieting.
        x + y
    }
}

/// Returns the minimum of two `f32` values, propagating NaN.
///
/// This behaves like IEEE 754-2019 minimum. In particular:
/// If one of the arguments is NaN, then a NaN is returned using the usual NaN propagation rules.
/// For this operation, -0.0 is considered to be strictly less than +0.0.
///
/// Note that, unlike most intrinsics, this is safe to call;
/// it does not require an `unsafe` block.
/// Therefore, implementations must not require the user to uphold
/// any safety invariants.
#[rustc_nounwind]
#[rustc_intrinsic]
pub const fn minimumf32(x: f32, y: f32) -> f32 {
    if x < y {
        x
    } else if y < x {
        y
    } else if x == y {
        if x.is_sign_negative() && y.is_sign_positive() { x } else { y }
    } else {
        // At least one input is NaN. Use `+` to perform NaN propagation and quieting.
        x + y
    }
}

/// Returns the minimum of two `f64` values, propagating NaN.
///
/// This behaves like IEEE 754-2019 minimum. In particular:
/// If one of the arguments is NaN, then a NaN is returned using the usual NaN propagation rules.
/// For this operation, -0.0 is considered to be strictly less than +0.0.
///
/// Note that, unlike most intrinsics, this is safe to call;
/// it does not require an `unsafe` block.
/// Therefore, implementations must not require the user to uphold
/// any safety invariants.
#[rustc_nounwind]
#[rustc_intrinsic]
pub const fn minimumf64(x: f64, y: f64) -> f64 {
    if x < y {
        x
    } else if y < x {
        y
    } else if x == y {
        if x.is_sign_negative() && y.is_sign_positive() { x } else { y }
    } else {
        // At least one input is NaN. Use `+` to perform NaN propagation and quieting.
        x + y
    }
}

/// Returns the minimum of two `f128` values, propagating NaN.
///
/// This behaves like IEEE 754-2019 minimum. In particular:
/// If one of the arguments is NaN, then a NaN is returned using the usual NaN propagation rules.
/// For this operation, -0.0 is considered to be strictly less than +0.0.
///
/// Note that, unlike most intrinsics, this is safe to call;
/// it does not require an `unsafe` block.
/// Therefore, implementations must not require the user to uphold
/// any safety invariants.
#[rustc_nounwind]
#[rustc_intrinsic]
pub const fn minimumf128(x: f128, y: f128) -> f128 {
    if x < y {
        x
    } else if y < x {
        y
    } else if x == y {
        if x.is_sign_negative() && y.is_sign_positive() { x } else { y }
    } else {
        // At least one input is NaN. Use `+` to perform NaN propagation and quieting.
        x + y
    }
}

/// Returns the maximum of two `f16` values, ignoring NaN.
///
/// This behaves like IEEE 754-2019 maximumNumber, *except* that it does not order signed
/// zeros deterministically. In particular:
/// If one of the arguments is NaN (quiet or signaling), then the other argument is returned. If
/// both arguments are NaN, returns NaN. If the inputs compare equal (such as for the case of `+0.0`
/// and `-0.0`), either input may be returned non-deterministically.
///
/// Note that, unlike most intrinsics, this is safe to call;
/// it does not require an `unsafe` block.
/// Therefore, implementations must not require the user to uphold
/// any safety invariants.
///
/// The stabilized version of this intrinsic is [`f16::max`].
#[rustc_nounwind]
#[rustc_intrinsic]
pub const fn maximum_number_nsz_f16(x: f16, y: f16) -> f16 {
    if x.is_nan() || y >= x {
        y
    } else {
        // Either y < x or y is a NaN.
        x
    }
}

/// Returns the maximum of two `f32` values, ignoring NaN.
///
/// This behaves like IEEE 754-2019 maximumNumber, *except* that it does not order signed
/// zeros deterministically. In particular:
/// If one of the arguments is NaN (quiet or signaling), then the other argument is returned. If
/// both arguments are NaN, returns NaN. If the inputs compare equal (such as for the case of `+0.0`
/// and `-0.0`), either input may be returned non-deterministically.
///
/// Note that, unlike most intrinsics, this is safe to call;
/// it does not require an `unsafe` block.
/// Therefore, implementations must not require the user to uphold
/// any safety invariants.
///
/// The stabilized version of this intrinsic is [`f32::max`].
#[rustc_nounwind]
#[rustc_intrinsic_const_stable_indirect]
#[rustc_intrinsic]
#[ferrocene::prevalidated]
pub const fn maximum_number_nsz_f32(x: f32, y: f32) -> f32 {
    if x.is_nan() || y >= x {
        y
    } else {
        // Either y < x or y is a NaN.
        x
    }
}

/// Returns the maximum of two `f64` values, ignoring NaN.
///
/// This behaves like IEEE 754-2019 maximumNumber, *except* that it does not order signed
/// zeros deterministically. In particular:
/// If one of the arguments is NaN (quiet or signaling), then the other argument is returned. If
/// both arguments are NaN, returns NaN. If the inputs compare equal (such as for the case of `+0.0`
/// and `-0.0`), either input may be returned non-deterministically.
///
/// Note that, unlike most intrinsics, this is safe to call;
/// it does not require an `unsafe` block.
/// Therefore, implementations must not require the user to uphold
/// any safety invariants.
///
/// The stabilized version of this intrinsic is [`f64::max`].
#[rustc_nounwind]
#[rustc_intrinsic_const_stable_indirect]
#[rustc_intrinsic]
pub const fn maximum_number_nsz_f64(x: f64, y: f64) -> f64 {
    if x.is_nan() || y >= x {
        y
    } else {
        // Either y < x or y is a NaN.
        x
    }
}

/// Returns the maximum of two `f128` values, ignoring NaN.
///
/// This behaves like IEEE 754-2019 maximumNumber, *except* that it does not order signed
/// zeros deterministically. In particular:
/// If one of the arguments is NaN (quiet or signaling), then the other argument is returned. If
/// both arguments are NaN, returns NaN. If the inputs compare equal (such as for the case of `+0.0`
/// and `-0.0`), either input may be returned non-deterministically.
///
/// Note that, unlike most intrinsics, this is safe to call;
/// it does not require an `unsafe` block.
/// Therefore, implementations must not require the user to uphold
/// any safety invariants.
///
/// The stabilized version of this intrinsic is [`f128::max`].
#[rustc_nounwind]
#[rustc_intrinsic]
pub const fn maximum_number_nsz_f128(x: f128, y: f128) -> f128 {
    if x.is_nan() || y >= x {
        y
    } else {
        // Either y < x or y is a NaN.
        x
    }
}

/// Returns the maximum of two `f16` values, propagating NaN.
///
/// This behaves like IEEE 754-2019 maximum. In particular:
/// If one of the arguments is NaN, then a NaN is returned using the usual NaN propagation rules.
/// For this operation, -0.0 is considered to be strictly less than +0.0.
///
/// Note that, unlike most intrinsics, this is safe to call;
/// it does not require an `unsafe` block.
/// Therefore, implementations must not require the user to uphold
/// any safety invariants.
#[rustc_nounwind]
#[rustc_intrinsic]
pub const fn maximumf16(x: f16, y: f16) -> f16 {
    if x > y {
        x
    } else if y > x {
        y
    } else if x == y {
        if x.is_sign_positive() && y.is_sign_negative() { x } else { y }
    } else {
        x + y
    }
}

/// Returns the maximum of two `f32` values, propagating NaN.
///
/// This behaves like IEEE 754-2019 maximum. In particular:
/// If one of the arguments is NaN, then a NaN is returned using the usual NaN propagation rules.
/// For this operation, -0.0 is considered to be strictly less than +0.0.
///
/// Note that, unlike most intrinsics, this is safe to call;
/// it does not require an `unsafe` block.
/// Therefore, implementations must not require the user to uphold
/// any safety invariants.
#[rustc_nounwind]
#[rustc_intrinsic]
pub const fn maximumf32(x: f32, y: f32) -> f32 {
    if x > y {
        x
    } else if y > x {
        y
    } else if x == y {
        if x.is_sign_positive() && y.is_sign_negative() { x } else { y }
    } else {
        x + y
    }
}

/// Returns the maximum of two `f64` values, propagating NaN.
///
/// This behaves like IEEE 754-2019 maximum. In particular:
/// If one of the arguments is NaN, then a NaN is returned using the usual NaN propagation rules.
/// For this operation, -0.0 is considered to be strictly less than +0.0.
///
/// Note that, unlike most intrinsics, this is safe to call;
/// it does not require an `unsafe` block.
/// Therefore, implementations must not require the user to uphold
/// any safety invariants.
#[rustc_nounwind]
#[rustc_intrinsic]
pub const fn maximumf64(x: f64, y: f64) -> f64 {
    if x > y {
        x
    } else if y > x {
        y
    } else if x == y {
        if x.is_sign_positive() && y.is_sign_negative() { x } else { y }
    } else {
        x + y
    }
}

/// Returns the maximum of two `f128` values, propagating NaN.
///
/// This behaves like IEEE 754-2019 maximum. In particular:
/// If one of the arguments is NaN, then a NaN is returned using the usual NaN propagation rules.
/// For this operation, -0.0 is considered to be strictly less than +0.0.
///
/// Note that, unlike most intrinsics, this is safe to call;
/// it does not require an `unsafe` block.
/// Therefore, implementations must not require the user to uphold
/// any safety invariants.
#[rustc_nounwind]
#[rustc_intrinsic]
pub const fn maximumf128(x: f128, y: f128) -> f128 {
    if x > y {
        x
    } else if y > x {
        y
    } else if x == y {
        if x.is_sign_positive() && y.is_sign_negative() { x } else { y }
    } else {
        x + y
    }
}

/// Returns the absolute value of a floating-point value.
///
/// The stabilized versions of this intrinsic are available on the float
/// primitives via the `abs` method. For example, [`f32::abs`].
#[rustc_nounwind]
#[rustc_intrinsic_const_stable_indirect]
#[rustc_intrinsic]
pub const fn fabs<T: bounds::FloatPrimitive>(x: T) -> T;

/// Copies the sign from `y` to `x` for `f16` values.
///
/// The stabilized version of this intrinsic is
/// [`f16::copysign`](../../std/primitive.f16.html#method.copysign)
#[rustc_nounwind]
#[rustc_intrinsic]
pub const fn copysignf16(x: f16, y: f16) -> f16;

/// Copies the sign from `y` to `x` for `f32` values.
///
/// The stabilized version of this intrinsic is
/// [`f32::copysign`](../../std/primitive.f32.html#method.copysign)
#[rustc_nounwind]
#[rustc_intrinsic_const_stable_indirect]
#[rustc_intrinsic]
pub const fn copysignf32(x: f32, y: f32) -> f32;
/// Copies the sign from `y` to `x` for `f64` values.
///
/// The stabilized version of this intrinsic is
/// [`f64::copysign`](../../std/primitive.f64.html#method.copysign)
#[rustc_nounwind]
#[rustc_intrinsic_const_stable_indirect]
#[rustc_intrinsic]
pub const fn copysignf64(x: f64, y: f64) -> f64;

/// Copies the sign from `y` to `x` for `f128` values.
///
/// The stabilized version of this intrinsic is
/// [`f128::copysign`](../../std/primitive.f128.html#method.copysign)
#[rustc_nounwind]
#[rustc_intrinsic]
pub const fn copysignf128(x: f128, y: f128) -> f128;

/// Generates the LLVM body for the automatic differentiation of `f` using Enzyme,
/// with `df` as the derivative function and `args` as its arguments.
///
/// Used internally as the body of `df` when expanding the `#[autodiff_forward]`
/// and `#[autodiff_reverse]` attribute macros.
///
/// Type Parameters:
/// - `F`: The original function to differentiate. Must be a function item.
/// - `G`: The derivative function. Must be a function item.
/// - `T`: A tuple of arguments passed to `df`.
/// - `R`: The return type of the derivative function.
///
/// This shows where the `autodiff` intrinsic is used during macro expansion:
///
/// ```rust,ignore (macro example)
/// #[autodiff_forward(df1, Dual, Const, Dual)]
/// pub fn f1(x: &[f64], y: f64) -> f64 {
///     unimplemented!()
/// }
/// ```
///
/// expands to:
///
/// ```rust,ignore (macro example)
/// #[rustc_autodiff]
/// #[inline(never)]
/// pub fn f1(x: &[f64], y: f64) -> f64 {
///     ::core::panicking::panic("not implemented")
/// }
/// #[rustc_autodiff(Forward, 1, Dual, Const, Dual)]
/// pub fn df1(x: &[f64], bx_0: &[f64], y: f64) -> (f64, f64) {
///     ::core::intrinsics::autodiff(f1::<>, df1::<>, (x, bx_0, y))
/// }
/// ```
#[rustc_nounwind]
#[rustc_intrinsic]
pub const fn autodiff<F, G, T: crate::marker::Tuple, R>(f: F, df: G, args: T) -> R;

/// Generates the LLVM body of a wrapper function to offload a kernel `f`.
///
/// Type Parameters:
/// - `F`: The kernel to offload. Must be a function item.
/// - `T`: A tuple of arguments passed to `f`.
/// - `R`: The return type of the kernel.
///
/// Arguments:
/// - `f`: The kernel function to offload.
/// - `workgroup_dim`: A 3D size specifying the number of workgroups to launch.
/// - `thread_dim`: A 3D size specifying the number of threads per workgroup.
/// - `args`: A tuple of arguments forwarded to `f`.
///
/// Example usage (pseudocode):
///
/// ```rust,ignore (pseudocode)
/// fn kernel(x: *mut [f64; 128]) {
///     core::intrinsics::offload(kernel_1, [256, 1, 1], [32, 1, 1], (x,))
/// }
///
/// #[cfg(target_os = "linux")]
/// extern "C" {
///     pub fn kernel_1(array_b: *mut [f64; 128]);
/// }
///
/// #[cfg(not(target_os = "linux"))]
/// #[rustc_offload_kernel]
/// extern "gpu-kernel" fn kernel_1(x: *mut [f64; 128]) {
///     unsafe { (*x)[0] = 21.0 };
/// }
/// ```
///
/// For reference, see the Clang documentation on offloading:
/// <https://clang.llvm.org/docs/OffloadingDesign.html>.
#[rustc_nounwind]
#[rustc_intrinsic]
pub const fn offload<F, T: crate::marker::Tuple, R>(
    f: F,
    workgroup_dim: [u32; 3],
    thread_dim: [u32; 3],
    dyn_cache: u32,
    args: T,
) -> R;

/// Inform Miri that a given pointer definitely has a certain alignment.
#[cfg(miri)]
#[rustc_allow_const_fn_unstable(const_eval_select)]
pub(crate) const fn miri_promise_symbolic_alignment(ptr: *const (), align: usize) {
    unsafe extern "Rust" {
        /// Miri-provided extern function to promise that a given pointer is properly aligned for
        /// "symbolic" alignment checks. Will fail if the pointer is not actually aligned or `align` is
        /// not a power of two. Has no effect when alignment checks are concrete (which is the default).
        fn miri_promise_symbolic_alignment(ptr: *const (), align: usize);
    }

    const_eval_select!(
        @capture { ptr: *const (), align: usize}:
        if const {
            // Do nothing.
        } else {
            // SAFETY: this call is always safe.
            unsafe {
                miri_promise_symbolic_alignment(ptr, align);
            }
        }
    )
}

/// Loads an argument of type `T` from the `va_list` `ap` and increment the
/// argument `ap` points to.
///
/// # Safety
///
/// This function is only sound to call when:
///
/// - there is a next variable argument available.
/// - the next argument's type must be ABI-compatible with the type `T`.
/// - the next argument must have a properly initialized value of type `T`.
///
/// Calling this function with an incompatible type, an invalid value, or when there
/// are no more variable arguments, is unsound.
///
#[rustc_intrinsic]
#[rustc_nounwind]
pub const unsafe fn va_arg<T: VaArgSafe>(ap: &mut VaList<'_>) -> T;

/// Duplicates a variable argument list. The returned list is initially at the same position as
/// the one in `src`, but can be advanced independently.
///
/// Codegen backends should not have custom behavior for this intrinsic, they should always use
/// this fallback implementation. This intrinsic *does not* map to the LLVM `va_copy` intrinsic.
///
/// This intrinsic exists only as a hook for Miri and constant evaluation, and is used to detect UB
/// when a variable argument list is used incorrectly.
#[rustc_intrinsic]
#[rustc_nounwind]
pub const fn va_copy<'f>(src: &VaList<'f>) -> VaList<'f> {
    // This fallback body exploits the fact that our codegen backends all just use
    // a plain memcpy to duplicate VaList. This assumption is wrong for Miri.
    assert!(!cfg!(miri), "fallback body is incorrect under Miri");

    src.duplicate()
}

/// Destroy the variable argument list `ap` after initialization with `va_start` (part of the
/// desugaring of `...`) or `va_copy`.
///
/// Code generation backends should not provide a custom implementation for this intrinsic. This
/// intrinsic *does not* map to the LLVM `va_end` intrinsic.
///
/// This function is a no-op on all current targets, but used as a hook for const evaluation to
/// detect UB when a variable argument list is used incorrectly.
///
/// # Safety
///
/// `ap` must not be used to access variable arguments after this call.
///
#[rustc_intrinsic]
#[rustc_nounwind]
pub const unsafe fn va_end(ap: &mut VaList<'_>) {
    /* deliberately does nothing */
}

/// Returns the return address of the caller function (after inlining) in a best-effort manner or a null pointer if it is not supported on the current backend.
/// Returning an accurate value is a quality-of-implementation concern, but no hard guarantees are
/// made about the return value: formally, the intrinsic non-deterministically returns
/// an arbitrary pointer without provenance.
///
/// Note that unlike most intrinsics, this is safe to call. This is because it only finds the return address of the immediate caller, which is guaranteed to be possible.
/// Other forms of the corresponding gcc or llvm intrinsic (which can have wildly unpredictable results or even crash at runtime) are not exposed.
#[rustc_intrinsic]
#[rustc_nounwind]
pub fn return_address() -> *const () {
    core::ptr::null()
}