[Bug target/72863] New: Powerpc64le: redundant swaps when using vec_vsx_ld/st

["anton at samba dot org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=72863

            Bug ID: 72863
           Summary: Powerpc64le: redundant swaps when using vec_vsx_ld/st
           Product: gcc
           Version: 7.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: anton at samba dot org
                CC: amodra at gcc dot gnu.org, bergner at gcc dot gnu.org,
                    meissner at gcc dot gnu.org, segher at gcc dot gnu.org,
                    wschmidt at gcc dot gnu.org
  Target Milestone: ---
            Target: powerpc64le-linux

I notice swaps to and from memory with the following test case:

void b(void)
{
        int i;

        unsigned char *s8 = src;
        unsigned char *d8 = dst;

        for (i = 0; i < 100; i++) {
                vector unsigned char vs = vec_vsx_ld(0, s8);
                vector unsigned char vd = vec_vsx_ld(0, d8);
                vector unsigned char vr = vec_xor(vs, vd);
                vec_vsx_st(vr, 0, d8);
                s8 += 16;
                d8 += 16;
        }
}

  70:   98 56 00 7c     lxvd2x  vs0,0,r10
  74:   98 4e 80 7d     lxvd2x  vs12,0,r9
  78:   10 00 4a 39     addi    r10,r10,16
  7c:   50 02 60 f1     xxswapd vs11,vs0
  80:   50 62 0c f0     xxswapd vs0,vs12
  84:   d0 04 0b f0     xxlxor  vs0,vs11,vs0
  88:   50 02 00 f0     xxswapd vs0,vs0
  8c:   98 4f 00 7c     stxvd2x vs0,0,r9
  90:   10 00 29 39     addi    r9,r9,16
  94:   dc ff 00 42     bdnz    70 <b+0x20>