[Bug tree-optimization/105735] New: GCC failed to reduce &= loop_inv in loop.

["crazylht at gmail dot com" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105735

            Bug ID: 105735
           Summary: GCC failed to reduce &= loop_inv in loop.
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: crazylht at gmail dot com
  Target Milestone: ---

This is another case from 47769, similar like 103462, but a little different.


unsigned long cfunc_one(unsigned long tmp, unsigned long bit2) {
    for (unsigned long bit = 0; bit < 64; bit++) {
        tmp &= bit2;
    }
    return tmp;
}


it should be equal to

unsigned long cfunc_one(unsigned long tmp, unsigned long bit2) {
   tmp &= bit2;
   return tmp;
}

but gcc generates a loop.

cfunc_one(unsigned long, unsigned long):
        mov     eax, 64
.L2:
        and     rdi, rsi
        dec     rax
        jne     .L2
        mov     rax, rdi
        ret

Similar for |= and ^=.