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From: "jakub at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug target/102143] ABI incompatibility with clang when passing
 32bit vectors on 32bit i686
Date: Wed, 01 Sep 2021 07:32:44 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D102143

--- Comment #4 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Well, we already have the ABI ISA dependent,
typedef int __v8si __attribute__((__vector_size__ (32)));

__v8si
foo (__v8si x, __v8si y)
{
  return x + y;
}
has different ABI based on -mavx or -mno-avx, etc.  For -mno-avx we emit a
warning:
/tmp/test.c: In function =E2=80=98foo=E2=80=99:
/tmp/test.c:5:1: warning: AVX vector return without AVX enabled changes the=
 ABI
[-Wpsabi]
    5 | {
      | ^
/tmp/test.c:4:1: note: the ABI for passing parameters with 32-byte alignment
has changed in GCC 4.6
    4 | foo (__v8si x, __v8si y)
      | ^~~
/tmp/test.c:4:1: warning: AVX vector argument without AVX enabled changes t=
he
ABI [-Wpsabi]

So, depending on what we decide, if the ABI will be ISA dependent, we want a
warning like the above one.=