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rustc_codegen_ssa: use bitcasts instead of type punning for scalar transmutes.

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Eduard-Mihai Burtescu 2020-12-07 17:33:43 +02:00
parent e5721a5283
commit 97c7022d08
2 changed files with 54 additions and 0 deletions
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19
compiler/rustc_codegen_ssa/src/mir/block.rs
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@ -1395,6 +1395,25 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
dst: PlaceRef<'tcx, Bx::Value>,
) {
let src = self.codegen_operand(bx, src);
// Special-case transmutes between scalars as simple bitcasts.
match (&src.layout.abi, &dst.layout.abi) {
(abi::Abi::Scalar(src_scalar), abi::Abi::Scalar(dst_scalar)) => {
// HACK(eddyb) LLVM doesn't like `bitcast`s between pointers and non-pointers.
if (src_scalar.value == abi::Pointer) == (dst_scalar.value == abi::Pointer) {
assert_eq!(src.layout.size, dst.layout.size);
// NOTE(eddyb) the `from_immediate` and `to_immediate_scalar`
// conversions allow handling `bool`s the same as `u8`s.
let src = bx.from_immediate(src.immediate());
let src_as_dst = bx.bitcast(src, bx.backend_type(dst.layout));
Immediate(bx.to_immediate_scalar(src_as_dst, dst_scalar)).store(bx, dst);
return;
}
}
_ => {}
}
let llty = bx.backend_type(src.layout);
let cast_ptr = bx.pointercast(dst.llval, bx.type_ptr_to(llty));
let align = src.layout.align.abi.min(dst.align);