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add a fallback implementation for the prefetch_* intrinsics

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The fallback is to just ignore the arguments. That is a valid implementation because this intrinsic is just a hint.

I also added `miri::intrinsic_fallback_is_spec` annotation, so that miri now supports these operations. A prefetch intrinsic call is valid on any pointer.
This commit is contained in:
Folkert de Vries 2025-08-19 21:12:53 +02:00
parent 16ad385579
commit 51df7aabbe
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2 changed files with 54 additions and 8 deletions
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39
library/core/src/intrinsics/mod.rs
View file

@ -261,7 +261,7 @@ pub unsafe fn atomic_fence<const ORD: AtomicOrdering>();
pub unsafe fn atomic_singlethreadfence<const ORD: AtomicOrdering>();
/// The `prefetch` intrinsic is a hint to the code generator to insert a prefetch instruction
/// if supported; otherwise, it is a no-op.
/// 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.
///
@ -271,9 +271,15 @@ pub unsafe fn atomic_singlethreadfence<const ORD: AtomicOrdering>();
/// This intrinsic does not have a stable counterpart.
#[rustc_intrinsic]
#[rustc_nounwind]
pub unsafe fn prefetch_read_data<T>(data: *const T, locality: i32);
#[miri::intrinsic_fallback_is_spec]
pub unsafe fn prefetch_read_data<T>(data: *const T, locality: i32) {
// This operation is a no-op, unless it is overridden by the backend.
let _ = data;
let _ = locality;
}
/// The `prefetch` intrinsic is a hint to the code generator to insert a prefetch instruction
/// if supported; otherwise, it is a no-op.
/// 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.
///
@ -283,9 +289,15 @@ pub unsafe fn prefetch_read_data<T>(data: *const T, locality: i32);
/// This intrinsic does not have a stable counterpart.
#[rustc_intrinsic]
#[rustc_nounwind]
pub unsafe fn prefetch_write_data<T>(data: *const T, locality: i32);
#[miri::intrinsic_fallback_is_spec]
pub unsafe fn prefetch_write_data<T>(data: *const T, locality: i32) {
// This operation is a no-op, unless it is overridden by the backend.
let _ = data;
let _ = locality;
}
/// The `prefetch` intrinsic is a hint to the code generator to insert a prefetch instruction
/// if supported; otherwise, it is a no-op.
/// 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.
///
@ -295,9 +307,15 @@ pub unsafe fn prefetch_write_data<T>(data: *const T, locality: i32);
/// This intrinsic does not have a stable counterpart.
#[rustc_intrinsic]
#[rustc_nounwind]
pub unsafe fn prefetch_read_instruction<T>(data: *const T, locality: i32);
#[miri::intrinsic_fallback_is_spec]
pub unsafe fn prefetch_read_instruction<T>(data: *const T, locality: i32) {
// This operation is a no-op, unless it is overridden by the backend.
let _ = data;
let _ = locality;
}
/// The `prefetch` intrinsic is a hint to the code generator to insert a prefetch instruction
/// if supported; otherwise, it is a no-op.
/// 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.
///
@ -307,7 +325,12 @@ pub unsafe fn prefetch_read_instruction<T>(data: *const T, locality: i32);
/// This intrinsic does not have a stable counterpart.
#[rustc_intrinsic]
#[rustc_nounwind]
pub unsafe fn prefetch_write_instruction<T>(data: *const T, locality: i32);
#[miri::intrinsic_fallback_is_spec]
pub unsafe fn prefetch_write_instruction<T>(data: *const T, locality: i32) {
// This operation is a no-op, unless it is overridden by the backend.
let _ = data;
let _ = locality;
}
/// Executes a breakpoint trap, for inspection by a debugger.
///

23
src/tools/miri/tests/pass/prefetch.rs Normal file
View file

@ -0,0 +1,23 @@
#![feature(core_intrinsics)]
fn main() {
static X: [u8; 8] = [0; 8];
unsafe {
::std::intrinsics::prefetch_read_data(::std::ptr::null::<u8>(), 1);
::std::intrinsics::prefetch_read_data(::std::ptr::dangling::<u8>(), 2);
::std::intrinsics::prefetch_read_data(X.as_ptr(), 3);
::std::intrinsics::prefetch_write_data(::std::ptr::null::<u8>(), 1);
::std::intrinsics::prefetch_write_data(::std::ptr::dangling::<u8>(), 2);
::std::intrinsics::prefetch_write_data(X.as_ptr(), 3);
::std::intrinsics::prefetch_read_instruction(::std::ptr::null::<u8>(), 1);
::std::intrinsics::prefetch_read_instruction(::std::ptr::dangling::<u8>(), 2);
::std::intrinsics::prefetch_read_instruction(X.as_ptr(), 3);
::std::intrinsics::prefetch_write_instruction(::std::ptr::null::<u8>(), 1);
::std::intrinsics::prefetch_write_instruction(::std::ptr::dangling::<u8>(), 2);
::std::intrinsics::prefetch_write_instruction(X.as_ptr(), 3);
}
}