[Bug target/103661] New: __builtin_cpu_supports returns a negative integer for avx512vbmi2

[stefan.kneifel at bluewin dot ch]

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?