bjoernager/rust
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Rollup merge of #114382 - scottmcm:compare-bytes-intrinsic, r=cjgillot

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Add a new `compare_bytes` intrinsic instead of calling `memcmp` directly

As discussed in #113435, this lets the backends be the place that can have the "don't call the function if n == 0" logic, if it's needed for the target.  (I didn't actually *add* those checks, though, since as I understood it we didn't actually need them on known targets?)

Doing this also let me make it `const` (unstable), which I don't think `extern "C" fn memcmp` can be.

cc `@RalfJung` `@Amanieu`
This commit is contained in:
Matthias Krüger 2023-08-07 05:29:12 +02:00 • committed by GitHub
commit cbe2522652
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17 changed files with 270 additions and 22 deletions
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22
compiler/rustc_const_eval/src/interpret/intrinsics.rs
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@ -261,6 +261,10 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
sym::write_bytes => {
self.write_bytes_intrinsic(&args[0], &args[1], &args[2])?;
}
sym::compare_bytes => {
let result = self.compare_bytes_intrinsic(&args[0], &args[1], &args[2])?;
self.write_scalar(result, dest)?;
}
sym::arith_offset => {
let ptr = self.read_pointer(&args[0])?;
let offset_count = self.read_target_isize(&args[1])?;
@ -643,6 +647,24 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
self.write_bytes_ptr(dst, bytes)
}
pub(crate) fn compare_bytes_intrinsic(
&mut self,
left: &OpTy<'tcx, <M as Machine<'mir, 'tcx>>::Provenance>,
right: &OpTy<'tcx, <M as Machine<'mir, 'tcx>>::Provenance>,
byte_count: &OpTy<'tcx, <M as Machine<'mir, 'tcx>>::Provenance>,
) -> InterpResult<'tcx, Scalar<M::Provenance>> {
let left = self.read_pointer(left)?;
let right = self.read_pointer(right)?;
let n = Size::from_bytes(self.read_target_usize(byte_count)?);
let left_bytes = self.read_bytes_ptr_strip_provenance(left, n)?;
let right_bytes = self.read_bytes_ptr_strip_provenance(right, n)?;
// `Ordering`'s discriminants are -1/0/+1, so casting does the right thing.
let result = Ord::cmp(left_bytes, right_bytes) as i32;
Ok(Scalar::from_i32(result))
}
pub(crate) fn raw_eq_intrinsic(
&mut self,
lhs: &OpTy<'tcx, <M as Machine<'mir, 'tcx>>::Provenance>,