[Bug tree-optimization/95863] New: Failure to detect table-based ctz implementation

[gabravier at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95863

            Bug ID: 95863
           Summary: Failure to detect table-based ctz implementation
           Product: gcc
           Version: 11.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: gabravier at gmail dot com
  Target Milestone: ---

int f(unsigned x)
{
    static const char table[32] = {0, 1, 28, 2, 29, 14, 24, 3, 30, 22, 20, 15,
25, 17, 4, 8, 31, 27, 13, 23, 21, 19, 16, 7, 26, 12, 18, 6, 11, 5, 10, 9};
    return table[((unsigned)((x & -x) * 0x077CB531U)) >> 27];
}

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90838 claims to optimize this code
to `return __builtin_ctz(x)`, but this does not occur.