[Bug tree-optimization/95230] New: Failure to optimize bit-scatter pattern to and 1

[gabravier at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95230

            Bug ID: 95230
           Summary: Failure to optimize bit-scatter pattern to and 1
           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: ---

uint32_t scatter(uint32_t val)
{
    uint32_t res = 0;
    uint32_t off = 0;

    for (uint32_t I = 0; I < 32; ++I)
        if (1 & (1 << I))
            res |= (val & (1 << off++)) << I;
    return res;
}

This can be optimized to `return val & 1;`. LLVM does this transformation, but
GCC does not. There is a more generic optimization that looks like it can be
done using something else than `1` as the left operand of the `&` in the `if`.