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Auto merge of #134757 - RalfJung:const_swap, r=scottmcm

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stabilize const_swap

libs-api FCP passed in https://github.com/rust-lang/rust/issues/83163.

However, I only just realized that this actually involves an intrinsic. The intrinsic could be implemented entirely with existing stable const functionality, but we choose to make it a primitive to be able to detect more UB. So nominating for `@rust-lang/lang`  to make sure they are aware; I leave it up to them whether they want to FCP this.

While at it I also renamed the intrinsic to make the "nonoverlapping" constraint more clear.

Fixes #83163
This commit is contained in:
bors 2024-12-30 23:46:42 +00:00
commit 4e5fec2f1e
28 changed files with 139 additions and 95 deletions
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2
compiler/rustc_codegen_ssa/src/mir/intrinsic.rs
View file

@ -75,7 +75,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
// If we're swapping something that's *not* an `OperandValue::Ref`,
// then we can do it directly and avoid the alloca.
// Otherwise, we'll let the fallback MIR body take care of it.
if let sym::typed_swap = name {
if let sym::typed_swap_nonoverlapping = name {
let pointee_ty = fn_args.type_at(0);
let pointee_layout = bx.layout_of(pointee_ty);
if !bx.is_backend_ref(pointee_layout)

2
compiler/rustc_codegen_ssa/src/traits/builder.rs
View file

@ -382,7 +382,7 @@ pub trait BuilderMethods<'a, 'tcx>:
/// Avoids `alloca`s for Immediates and ScalarPairs.
///
/// FIXME: Maybe do something smarter for Ref types too?
/// For now, the `typed_swap` intrinsic just doesn't call this for those
/// For now, the `typed_swap_nonoverlapping` intrinsic just doesn't call this for those
/// cases (in non-debug), preferring the fallback body instead.
fn typed_place_swap(
&mut self,