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From: "crazylht at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/105735] New: GCC failed to reduce &= loop_inv
 in loop.
Date: Thu, 26 May 2022 07:54:55 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D105735

            Bug ID: 105735
           Summary: GCC failed to reduce &=3D 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 differen=
t.


unsigned long cfunc_one(unsigned long tmp, unsigned long bit2) {
    for (unsigned long bit =3D 0; bit < 64; bit++) {
        tmp &=3D bit2;
    }
    return tmp;
}


it should be equal to

unsigned long cfunc_one(unsigned long tmp, unsigned long bit2) {
   tmp &=3D 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 |=3D and ^=3D.=