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Auto merge of #121668 - erikdesjardins:commonprim, r=scottmcm,oli-obk

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Represent `Result<usize, Box<T>>` as ScalarPair(i64, ptr)

This allows types like `Result<usize, std::io::Error>` (and integers of differing sign, e.g. `Result<u64, i64>`) to be passed in a pair of registers instead of through memory, like `Result<u64, u64>` or `Result<Box<T>, Box<U>>` are today.

Fixes #97540.

r? `@ghost`
This commit is contained in:
bors 2024-03-13 15:25:35 +00:00
commit 3cbb93223f
7 changed files with 222 additions and 19 deletions
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34
compiler/rustc_abi/src/layout.rs
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@ -816,15 +816,37 @@ where
break;
}
};
if let Some(pair) = common_prim {
// This is pretty conservative. We could go fancier
// by conflating things like i32 and u32, or even
// realising that (u8, u8) could just cohabit with
// u16 or even u32.
if pair != (prim, offset) {
if let Some((old_prim, common_offset)) = common_prim {
// All variants must be at the same offset
if offset != common_offset {
common_prim = None;
break;
}
// This is pretty conservative. We could go fancier
// by realising that (u8, u8) could just cohabit with
// u16 or even u32.
let new_prim = match (old_prim, prim) {
// Allow all identical primitives.
(x, y) if x == y => x,
// Allow integers of the same size with differing signedness.
// We arbitrarily choose the signedness of the first variant.
(p @ Primitive::Int(x, _), Primitive::Int(y, _)) if x == y => p,
// Allow integers mixed with pointers of the same layout.
// We must represent this using a pointer, to avoid
// roundtripping pointers through ptrtoint/inttoptr.
(p @ Primitive::Pointer(_), i @ Primitive::Int(..))
| (i @ Primitive::Int(..), p @ Primitive::Pointer(_))
if p.size(dl) == i.size(dl) && p.align(dl) == i.align(dl) =>
{
p
}
_ => {
common_prim = None;
break;
}
};
// We may be updating the primitive here, for example from int->ptr.
common_prim = Some((new_prim, common_offset));
} else {
common_prim = Some((prim, offset));
}