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Windows x86: Change i128 to return via the vector ABI

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Clang and GCC both return `i128` in xmm0 on windows-msvc and
windows-gnu. Currently, Rust returns the type on the stack. Add a
calling convention adjustment so we also return scalar `i128`s using the
vector ABI, which makes our `i128` compatible with C.

In the future, Clang may change to return `i128` on the stack for its
`-msvc` targets (more at [1]). If this happens, the change here will
need to be adjusted to only affect MinGW.

Link: https://github.com/rust-lang/rust/issues/134288
This commit is contained in:
Trevor Gross 2024-12-14 00:32:39 +00:00
parent 581e0ac90c
commit a44a20ee4a
5 changed files with 44 additions and 67 deletions
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20
compiler/rustc_target/src/callconv/x86_win64.rs
View file

@ -1,4 +1,4 @@
use rustc_abi::{BackendRepr, Float, Primitive};
use rustc_abi::{BackendRepr, Float, Integer, Primitive, RegKind, Size};
use crate::abi::call::{ArgAbi, FnAbi, Reg};
use crate::spec::HasTargetSpec;
@ -6,7 +6,7 @@ use crate::spec::HasTargetSpec;
// Win64 ABI: https://docs.microsoft.com/en-us/cpp/build/parameter-passing
pub(crate) fn compute_abi_info<Ty>(_cx: &impl HasTargetSpec, fn_abi: &mut FnAbi<'_, Ty>) {
let fixup = |a: &mut ArgAbi<'_, Ty>| {
let fixup = |a: &mut ArgAbi<'_, Ty>, is_ret: bool| {
match a.layout.backend_repr {
BackendRepr::Uninhabited | BackendRepr::Memory { sized: false } => {}
BackendRepr::ScalarPair(..) | BackendRepr::Memory { sized: true } => {
@ -23,11 +23,16 @@ pub(crate) fn compute_abi_info<Ty>(_cx: &impl HasTargetSpec, fn_abi: &mut FnAbi<
// (probably what clang calls "illegal vectors").
}
BackendRepr::Scalar(scalar) => {
// Match what LLVM does for `f128` so that `compiler-builtins` builtins match up
// with what LLVM expects.
if a.layout.size.bytes() > 8
if is_ret && matches!(scalar.primitive(), Primitive::Int(Integer::I128, _)) {
// `i128` is returned in xmm0 by Clang and GCC
// FIXME(#134288): This may change for the `-msvc` targets in the future.
let reg = Reg { kind: RegKind::Vector, size: Size::from_bits(128) };
a.cast_to(reg);
} else if a.layout.size.bytes() > 8
&& !matches!(scalar.primitive(), Primitive::Float(Float::F128))
{
// Match what LLVM does for `f128` so that `compiler-builtins` builtins match up
// with what LLVM expects.
a.make_indirect();
} else {
a.extend_integer_width_to(32);
@ -37,8 +42,9 @@ pub(crate) fn compute_abi_info<Ty>(_cx: &impl HasTargetSpec, fn_abi: &mut FnAbi<
};
if !fn_abi.ret.is_ignore() {
fixup(&mut fn_abi.ret);
fixup(&mut fn_abi.ret, true);
}
for arg in fn_abi.args.iter_mut() {
if arg.is_ignore() && arg.layout.is_zst() {
// Windows ABIs do not talk about ZST since such types do not exist in MSVC.
@ -49,7 +55,7 @@ pub(crate) fn compute_abi_info<Ty>(_cx: &impl HasTargetSpec, fn_abi: &mut FnAbi<
arg.make_indirect_from_ignore();
continue;
}
fixup(arg);
fixup(arg, false);
}
// FIXME: We should likely also do something about ZST return types, similar to above.
// However, that's non-trivial due to `()`.