[Bug c/82940] New: Suboptimal code for (a & 0x7f) | (b & 0x80) on powerpc

christophe.leroy@c-s.fr gcc-bugzilla@gcc.gnu.org
Fri Nov 10 15:39:00 GMT 2017


https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82940

            Bug ID: 82940
           Summary: Suboptimal code for (a & 0x7f) | (b & 0x80) on powerpc
           Product: gcc
           Version: 5.4.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: christophe.leroy@c-s.fr
  Target Milestone: ---

unsigned char g(unsigned char t[], unsigned char v)
{
        return (t[v & 0x7f] & 0x7f) | (v & 0x80);
}

00000008 <g>:
   8:   54 89 06 7e     clrlwi  r9,r4,25
   c:   7c 63 48 ae     lbzx    r3,r3,r9
  10:   54 84 00 30     rlwinm  r4,r4,0,0,24
  14:   54 63 06 7e     clrlwi  r3,r3,25
  18:   7c 63 23 78     or      r3,r3,r4
  1c:   4e 80 00 20     blr


I would expect

00000008 <g>:
   8:   54 89 06 7e     clrlwi  r9,r4,25
   c:   7c 63 48 ae     lbzx    r3,r3,r9
  10:   54 84 00 30     rlwimi  r3,r4,0,24,24
  14:   4e 80 00 20     blr


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