[Bug diagnostics/128554] New: Bogus -Wshift-count-negative warning for __builtin_stdc_bit_floor with a zero-valued const variable

[yuki.tanaka at defaultcase dot de via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=128554

            Bug ID: 128554
           Summary: Bogus -Wshift-count-negative warning for
                    __builtin_stdc_bit_floor with a zero-valued const
                    variable
           Product: gcc
           Version: 17.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: diagnostics
          Assignee: dmalcolm at redhat dot com
          Reporter: yuki.tanaka at defaultcase dot de
  Target Milestone: ---

unsigned f(void)
{
  const unsigned char c = 0;

  return __builtin_stdc_bit_floor(c);
}

With -O2, GCC warns:

warning: left shift count is negative [-Wshift-count-negative]

The source contains no shift operation.

Compiler Explorer:
https://godbolt.org/z/bfTsdYj34