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From: "stefan.kneifel at bluewin dot ch" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/103661] New: __builtin_cpu_supports returns a negative integer for avx512vbmi2
Date: Sat, 11 Dec 2021 16:56:17 +0000	[thread overview]
Message-ID: <bug-103661-4@http.gcc.gnu.org/bugzilla/> (raw)

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103661

            Bug ID: 103661
           Summary: __builtin_cpu_supports returns a negative integer for
                    avx512vbmi2
           Product: gcc
           Version: 11.2.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: stefan.kneifel at bluewin dot ch
  Target Milestone: ---

__builtin_cpu_supports is supposed to return a positive integer if the run-time
CPU supports the requested feature and zero otherwise (see Documentation).
However, for the feature "avx512vbmi2", a negative integer (0x80000000) is
returned.

FEATURE_AVX512VBMI2 equals to 31 in gcc/common/config/i386/i386-cpuinfo.h, thus
the returned 32-bit integer has bit 31 set and is therefore negative.

This might lead to surprising errors even inside GCC (e.g. when features are
tested in automatically generated resolvers; the code seems to rely on the
positivity).

Would it be an acceptable solution to declare __builtin_cpu_supports as
unsigned, or do you see another solution?

             reply	other threads:[~2021-12-11 16:56 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-12-11 16:56 stefan.kneifel at bluewin dot ch [this message]
2021-12-11 18:08 ` [Bug target/103661] " pinskia at gcc dot gnu.org
2021-12-11 18:08 ` pinskia at gcc dot gnu.org
2021-12-11 23:50 ` stefan.kneifel at bluewin dot ch
2021-12-12 12:50 ` stefan.kneifel at bluewin dot ch
2021-12-13 10:12 ` marxin at gcc dot gnu.org
2021-12-15  9:31 ` cvs-commit at gcc dot gnu.org
2021-12-15 10:52 ` marxin at gcc dot gnu.org
2021-12-15 10:52 ` marxin at gcc dot gnu.org
2021-12-16 11:46 ` cvs-commit at gcc dot gnu.org
2021-12-16 13:03 ` cvs-commit at gcc dot gnu.org
2021-12-16 13:04 ` marxin at gcc dot gnu.org

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