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Auto merge of #116510 - scottmcm:no-1-simd-v2, r=compiler-errors

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Copy 1-element arrays as scalars, not vectors

For `[T; 1]` it's silly to copy as `<1 x T>` when we can just copy as `T`.

Inspired by https://github.com/rust-lang/rust/issues/101210#issuecomment-1732470941, which pointed out that `Option<[u8; 1]>` was codegenning worse than `Option<u8>`.

(I'm not sure *why* LLVM doesn't optimize out `<1 x u8>`, but might as well just not emit it in the first place in this codepath.)

---

I think I bit off too much in #116479; let me try just the scalar case first.

r? `@ghost`
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bors 2023-10-12 18:45:01 +00:00
commit df4379b4eb
4 changed files with 81 additions and 1 deletions
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7
compiler/rustc_codegen_llvm/src/type_of.rs
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@ -397,7 +397,12 @@ impl<'tcx> LayoutLlvmExt<'tcx> for TyAndLayout<'tcx> {
// extracts all the individual values.
let ety = element.llvm_type(cx);
return Some(cx.type_vector(ety, *count));
if *count == 1 {
// Emitting `<1 x T>` would be silly; just use the scalar.
return Some(ety);
} else {
return Some(cx.type_vector(ety, *count));
}
}
// FIXME: The above only handled integer arrays; surely more things