Auto merge of #77434 - jonas-schievink:ret-in-reg-2-electric-boogalo, r=nagisa
Returns values up to 2*usize by value Addresses https://github.com/rust-lang/rust/pull/76986#discussion_r498306837 and https://github.com/rust-lang/rust/pull/76986#issuecomment-696415287 by doing the optimization on all targets. This matches what we do for functions returning `&[T]` and other fat pointers, so it should be Harmless™
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@ -2787,8 +2787,9 @@ where
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_ => return,
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}
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let max_by_val_size =
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if is_ret { call::max_ret_by_val(cx) } else { Pointer.size(cx) };
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// Return structures up to 2 pointers in size by value, matching `ScalarPair`. LLVM
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// will usually return these in 2 registers, which is more efficient than by-ref.
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let max_by_val_size = if is_ret { Pointer.size(cx) * 2 } else { Pointer.size(cx) };
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let size = arg.layout.size;
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if arg.layout.is_unsized() || size > max_by_val_size {
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@ -610,15 +610,3 @@ impl<'a, Ty> FnAbi<'a, Ty> {
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Ok(())
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}
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}
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/// Returns the maximum size of return values to be passed by value in the Rust ABI.
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///
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/// Return values beyond this size will use an implicit out-pointer instead.
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pub fn max_ret_by_val<C: HasTargetSpec + HasDataLayout>(spec: &C) -> Size {
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match spec.target_spec().arch.as_str() {
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// System-V will pass return values up to 128 bits in RAX/RDX.
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"x86_64" => Size::from_bits(128),
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_ => spec.data_layout().pointer_size,
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}
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}
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