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From: "mkretz at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug libstdc++/115308] New: std::experimental::simd<char> is not
 convertible to NEON intrinsic type with Clang
Date: Fri, 31 May 2024 14:17:56 +0000
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X-Bugzilla-Product: gcc
X-Bugzilla-Component: libstdc++
X-Bugzilla-Version: 15.0
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X-Bugzilla-Who: mkretz at gcc dot gnu.org
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D115308

            Bug ID: 115308
           Summary: std::experimental::simd<char> is not convertible to
                    NEON intrinsic type with Clang
           Product: gcc
           Version: 15.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
          Assignee: mkretz at gcc dot gnu.org
          Reporter: mkretz at gcc dot gnu.org
  Target Milestone: ---
            Target: arm-*-*, aarch64-*-*

std::experimental::parallelism_v2::__int_for_sizeof<1>() returns 'char' ins=
tead
of 'signed char' if __clang__ is defined. With -fno-signed-char that's an
observable bug.

https://github.com/VcDevel/std-simd/commit/2f99e2813fc751d2493ad79bc1aec3ce=
64c7c49e
is the commit that introduced it (before the merge to libstdc++). "Use char=
 for
1
byte and long long for 8 bytes. This is necessary to match the return vector
type of vector compares."
I'm taking a guess here that this is due to GCC applying
-flax-vector-conversions on vector compare results and Clang probably doesn=
't
do it. But that still doesn't really justify returning 'char' unconditional=
ly
for trait that is supposed to return a signed integer type.

The mask type issue must be solved differently, so that __int_for_sizeof can
return the right type again.

All releases of GCC are affected.=