https://gcc.gnu.org/g:e63a873f1df7493b8b657acafb451bf40166044e
commit r17-2359-ge63a873f1df7493b8b657acafb451bf40166044e Author: Oleg Tolmatcev <[email protected]> Date: Sun Jun 14 00:22:07 2026 +0200 i386: Fix Win64 __int128 return handling [PR78799] GCC could return __int128 values in SSE (%xmm0) on Windows x64 instead of following the MS x64 ABI. Root cause: return classification allowed 128-bit integer-like scalars to be treated as direct register returns. This patch updates the Windows x64 return-classification and codegen to treat int128 as an indirect return (caller-provided slot passed as first argument, pointer returned in RAX). gcc: PR target/78799 * config/i386/i386.cc (function_value_ms_64): Do not treat integral 16-byte values as SSE returns. (ix86_return_in_memory): Likewise avoid treating integral 16-byte values as XMM returns. gcc/testsuite: * gcc.target/i386/pr78799.c: New test. Signed-off-by: Oleg Tolmatcev <[email protected]> Signed-off-by: Jonathan Yong <[email protected]> Diff: --- gcc/config/i386/i386.cc | 6 ++---- gcc/testsuite/gcc.target/i386/pr78799.c | 15 +++++++++++++++ 2 files changed, 17 insertions(+), 4 deletions(-) diff --git a/gcc/config/i386/i386.cc b/gcc/config/i386/i386.cc index 23f65ab401d1..31a057e81cd9 100644 --- a/gcc/config/i386/i386.cc +++ b/gcc/config/i386/i386.cc @@ -4348,10 +4348,9 @@ function_value_ms_64 (machine_mode orig_mode, machine_mode mode, break; if (valtype != NULL_TREE && !VECTOR_INTEGER_TYPE_P (valtype) - && !INTEGRAL_TYPE_P (valtype) && !VECTOR_FLOAT_TYPE_P (valtype)) break; - if ((SCALAR_INT_MODE_P (mode) || VECTOR_MODE_P (mode)) + if (VECTOR_MODE_P (mode) && !COMPLEX_MODE_P (mode)) regno = FIRST_SSE_REG; break; @@ -4458,9 +4457,8 @@ ix86_return_in_memory (const_tree type, const_tree fntype ATTRIBUTE_UNUSED) /* __m128 is returned in xmm0. 256/512-bit vector values are returned in ymm0/zmm0 when AVX/AVX512 is enabled. */ if ((!type || VECTOR_INTEGER_TYPE_P (type) - || INTEGRAL_TYPE_P (type) || VECTOR_FLOAT_TYPE_P (type)) - && (SCALAR_INT_MODE_P (mode) || VECTOR_MODE_P (mode)) + && VECTOR_MODE_P (mode) && !COMPLEX_MODE_P (mode) && ((GET_MODE_SIZE (mode) == 16 || size == 16) || (TARGET_AVX && (GET_MODE_SIZE (mode) == 32 || size == 32)) diff --git a/gcc/testsuite/gcc.target/i386/pr78799.c b/gcc/testsuite/gcc.target/i386/pr78799.c new file mode 100644 index 000000000000..fcd6fe3c9d8a --- /dev/null +++ b/gcc/testsuite/gcc.target/i386/pr78799.c @@ -0,0 +1,15 @@ +/* { dg-do compile { target { x86_64-*-mingw* } } } */ +/* { dg-options "-O2" } */ + +/* PR78799: verify Win64 __int128 return uses an indirect sret-style path: + RCX points to the return slot, RDX points to the argument object. */ +__attribute__((ms_abi, noinline, noclone)) +__int128 +ret_i128 (__int128 a) +{ + return a; +} + +/* { dg-final { scan-assembler "movdqa\t\\(%rdx\\), %xmm0" } } */ +/* { dg-final { scan-assembler "movq\t%rcx, %rax" } } */ +/* { dg-final { scan-assembler "movaps\t%xmm0, \\(%rcx\\)" } } */
