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Auto merge of #112157 - erikdesjardins:align, r=nikic

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Resurrect: rustc_target: Add alignment to indirectly-passed by-value types, correcting the alignment of byval on x86 in the process.

Same as #111551, which I [accidentally closed](https://github.com/rust-lang/rust/pull/111551#issuecomment-1571222612) :/

---

This resurrects PR #103830, which has sat idle for a while.

Beyond #103830, this also:
- fixes byval alignment for types containing vectors on Darwin (see `tests/codegen/align-byval-vector.rs`)
- fixes byval alignment for overaligned types on x86 Windows (see `tests/codegen/align-byval.rs`)
- fixes ABI for types with 128bit requested alignment on ARM64 Linux (see `tests/codegen/aarch64-struct-align-128.rs`)

r? `@nikic`

---

`@pcwalton's` original PR description is reproduced below:

Commit 88e4d2c from five years ago removed
support for alignment on indirectly-passed arguments because of problems with
the `i686-pc-windows-msvc` target. Unfortunately, the `memcpy` optimizations I
recently added to LLVM 16 depend on this to forward `memcpy`s. This commit
attempts to fix the problems with `byval` parameters on that target and now
correctly adds the `align` attribute.

The problem is summarized in [this comment] by `@eddyb.` Briefly, 32-bit x86 has
special alignment rules for `byval` parameters: for the most part, their
alignment is forced to 4. This is not well-documented anywhere but in the Clang
source. I looked at the logic in Clang `TargetInfo.cpp` and tried to replicate
it here. The relevant methods in that file are
`X86_32ABIInfo::getIndirectResult()` and
`X86_32ABIInfo::getTypeStackAlignInBytes()`. The `align` parameter attribute
for `byval` parameters in LLVM must match the platform ABI, or miscompilations
will occur. Note that this doesn't use the approach suggested by eddyb, because
I felt it was overkill to store the alignment in `on_stack` when special
handling is really only needed for 32-bit x86.

As a side effect, this should fix #80127, because it will make the `align`
parameter attribute for `byval` parameters match the platform ABI on LLVM
x86-64.

[this comment]: #80822 (comment)
This commit is contained in:
bors 2023-07-15 15:39:53 +00:00
commit 7a17f577b3
32 changed files with 1251 additions and 93 deletions
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10
compiler/rustc_ty_utils/src/layout.rs
View file

@ -258,6 +258,8 @@ fn layout_of_uncached<'tcx>(
largest_niche,
align: element.align,
size,
max_repr_align: None,
unadjusted_abi_align: element.align.abi,
})
}
ty::Slice(element) => {
@ -269,6 +271,8 @@ fn layout_of_uncached<'tcx>(
largest_niche: None,
align: element.align,
size: Size::ZERO,
max_repr_align: None,
unadjusted_abi_align: element.align.abi,
})
}
ty::Str => tcx.mk_layout(LayoutS {
@ -278,6 +282,8 @@ fn layout_of_uncached<'tcx>(
largest_niche: None,
align: dl.i8_align,
size: Size::ZERO,
max_repr_align: None,
unadjusted_abi_align: dl.i8_align.abi,
}),
// Odd unit types.
@ -431,6 +437,8 @@ fn layout_of_uncached<'tcx>(
largest_niche: e_ly.largest_niche,
size,
align,
max_repr_align: None,
unadjusted_abi_align: align.abi,
})
}
@ -884,6 +892,8 @@ fn generator_layout<'tcx>(
largest_niche: prefix.largest_niche,
size,
align,
max_repr_align: None,
unadjusted_abi_align: align.abi,
});
debug!("generator layout ({:?}): {:#?}", ty, layout);
Ok(layout)