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core: disable ptr::swap_nonoverlapping_one's block optimization on SPIR-V.

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Eduard-Mihai Burtescu 2021-03-11 16:33:34 +02:00
parent 3c3d3ddde9
commit bc6af97ed0
1 changed files with 17 additions and 6 deletions
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23
library/core/src/ptr/mod.rs
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@ -473,12 +473,23 @@ pub const fn slice_from_raw_parts_mut<T>(data: *mut T, len: usize) -> *mut [T] {
#[inline]
#[rustc_const_unstable(feature = "const_swap", issue = "83163")]
pub(crate) const unsafe fn swap_nonoverlapping_one<T>(x: *mut T, y: *mut T) {
// Only apply the block optimization in `swap_nonoverlapping_bytes` for types
// at least as large as the block size, to avoid pessimizing codegen.
if mem::size_of::<T>() >= 32 {
// SAFETY: the caller must uphold the safety contract for `swap_nonoverlapping`.
unsafe { swap_nonoverlapping(x, y, 1) };
return;
// NOTE(eddyb) SPIR-V's Logical addressing model doesn't allow for arbitrary
// reinterpretation of values as (chunkable) byte arrays, and the loop in the
// block optimization in `swap_nonoverlapping_bytes` is hard to rewrite back
// into the (unoptimized) direct swapping implementation, so we disable it.
// FIXME(eddyb) the block optimization also prevents MIR optimizations from
// understanding `mem::replace`, `Option::take`, etc. - a better overall
// solution might be to make `swap_nonoverlapping` into an intrinsic, which
// a backend can choose to implement using the block optimization, or not.
#[cfg(not(target_arch = "spirv"))]
{
// Only apply the block optimization in `swap_nonoverlapping_bytes` for types
// at least as large as the block size, to avoid pessimizing codegen.
if mem::size_of::<T>() >= 32 {
// SAFETY: the caller must uphold the safety contract for `swap_nonoverlapping`.
unsafe { swap_nonoverlapping(x, y, 1) };
return;
}
}
// Direct swapping, for the cases not going through the block optimization.