https://llvm.org/bugs/show_bug.cgi?id=28975
Bug ID: 28975
Summary: ABI incompatibilities between Clang and GCC (calling
conventions for AVX512 vector arguments)
Product: libraries
Version: trunk
Hardware: PC
OS: All
Status: NEW
Severity: normal
Priority: P
Component: Backend: X86
Assignee: unassignedb...@nondot.org
Reporter: wenzel.ja...@epfl.ch
CC: llvm-bugs@lists.llvm.org
Classification: Unclassified
Consider the following simple program:
------------------------
#include <immintrin.h>
float test_float(float x) { return x; }
double test_double(double x) { return x; }
__m128 test_m128(__m128 x) { return x; }
__m256 test_m256(__m256 x) { return x; }
__m512 test_m512(__m512 x) { return x; }
------------------------
GCC trunk compiles this to the following optimized assembly (labels stripped
away for readability):
$ gcc test.c -O3 -Wall -Wabi -mavx512f -fomit-frame-pointer -o - -S
_test_f1:
ret
_test_f4:
ret
_test_f8:
ret
_test_f16:
ret
In other words, everything is passed via registers. On the other hand, clang
uses registers for everything *except* AVX512 SIMD registers:
$ clang test.c -O3 -Wall -Wabi -mavx512f -fomit-frame-pointer -o - -S
_test_f1:
retq
_test_f4:
retq
_test_f8:
retq
_test_f16:
pushq %rbp
movq %rsp, %rbp
andq $-64, %rsp
subq $64, %rsp
vmovaps 16(%rbp), %ymm0
vmovaps 48(%rbp), %ymm1
vmovaps %ymm1, 32(%rdi)
vmovaps %ymm0, (%rdi)
movq %rdi, %rax
movq %rbp, %rsp
popq %rbp
retq
It would be desirable if Clang would match GCC's behavior here.
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