Rollup merge of #137094 - RalfJung:softfloat-means-no-simd, r=tgross35

x86_win64 ABI: do not use xmm0 with softfloat ABI

This adjusts https://github.com/rust-lang/rust/pull/134290 to not apply the new logic to targets marked as "softfloat". That fixes most instances of the issue brought up [here](https://github.com/rust-lang/rust/issues/116558#issuecomment-2661027437).

r? `@tgross35`

1 files changed, 10 insertions, 6 deletions

diff --git a/compiler/rustc_target/src/callconv/x86_win64.rs b/compiler/rustc_target/src/callconv/x86_win64.rs
index 23ef2cf8284..2ef5127de04 100644
--- a/compiler/rustc_target/src/callconv/x86_win64.rs
+++ b/compiler/rustc_target/src/callconv/x86_win64.rs
@@ -1,11 +1,11 @@
 use rustc_abi::{BackendRepr, Float, Integer, Primitive, RegKind, Size};
 
 use crate::callconv::{ArgAbi, FnAbi, Reg};
-use crate::spec::HasTargetSpec;
+use crate::spec::{HasTargetSpec, RustcAbi};
 
 // 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>) {
+pub(crate) fn compute_abi_info<Ty>(cx: &impl HasTargetSpec, fn_abi: &mut FnAbi<'_, Ty>) {
     let fixup = |a: &mut ArgAbi<'_, Ty>, is_ret: bool| {
         match a.layout.backend_repr {
             BackendRepr::Uninhabited | BackendRepr::Memory { sized: false } => {}
@@ -24,10 +24,14 @@ pub(crate) fn compute_abi_info<Ty>(_cx: &impl HasTargetSpec, fn_abi: &mut FnAbi<
             }
             BackendRepr::Scalar(scalar) => {
                 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);
+                    if cx.target_spec().rustc_abi == Some(RustcAbi::X86Softfloat) {
+                        // Use the native `i128` LLVM type for the softfloat ABI -- in other words, adjust nothing.
+                    } else {
+                        // `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))
                 {