rust/tests/codegen/align-byval.rs

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rustc_target: Add alignment to indirectly-passed by-value types, correcting the alignment of `byval` on x86 in the process. Commit 88e4d2c2918428d55e34cd57c11279ea839c8822 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]: https://github.com/rust-lang/rust/pull/80822#issuecomment-829985417
2022-10-31 20:38:40 -07:00
// ignore-x86
// ignore-aarch64
// ignore-aarch64_be
// ignore-arm
// ignore-armeb
// ignore-avr
// ignore-bpfel
// ignore-bpfeb
// ignore-hexagon
// ignore-mips
// ignore-mips64
// ignore-msp430
// ignore-powerpc64
// ignore-powerpc64le
// ignore-powerpc
// ignore-r600
// ignore-amdgcn
// ignore-sparc
// ignore-sparcv9
// ignore-sparcel
// ignore-s390x
// ignore-tce
// ignore-thumb
// ignore-thumbeb
// ignore-xcore
// ignore-nvptx
// ignore-nvptx64
// ignore-le32
// ignore-le64
// ignore-amdil
// ignore-amdil64
// ignore-hsail
// ignore-hsail64
// ignore-spir
// ignore-spir64
// ignore-kalimba
// ignore-shave
//
// Tests that `byval` alignment is properly specified (#80127).
// The only targets that use `byval` are m68k, wasm, x86-64, and x86. Note that
// x86 has special rules (see #103830), and it's therefore ignored here.
#[repr(C)]
#[repr(align(16))]
struct Foo {
a: [i32; 16],
}
extern "C" {
// CHECK: declare void @f({{.*}}byval(%Foo) align 16{{.*}})
fn f(foo: Foo);
}
pub fn main() {
unsafe { f(Foo { a: [1; 16] }) }
}