[Bug target/61837] New: missed loop invariant expression optimization

[carrot at google dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61837

            Bug ID: 61837
           Summary: missed loop invariant expression optimization
           Product: gcc
           Version: 4.10.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: carrot at google dot com
              Host: x86_64-unknown-linux-gnu
            Target: powerpc64le

Compile following code with trunk compiler and options -O2 -m64 -mcpu=power8

void foo(int *p1, char *p2, int s)
{
  int n, v, i;

  v = 0;
  for (n = 0; n <= 100; n++) {
     for (i = 0; i < s; i++)
        if (p2[i] == n)
           p1[i] = v;
     v += 88;
  }
}

I got

foo:
    addi 9,5,-1
    cmpwi 5,5,0
    rldicl 9,9,0,32
    li 6,0
    li 7,0
    add 5,4,9
    .p2align 4,,15
.L2:
    ble 5,.L6
    addi 8,4,-1
    mr 10,3
    subf 9,8,5     // A
    mtctr 9
    b .L4
    .p2align 4,,15
.L3:
    addi 10,10,4
    bdz .L6
.L4:
    lbzu 9,1(8)
    cmpw 7,9,7
    bne 7,.L3
    stw 6,0(10)
    addi 10,10,4
    bdnz .L4
.L6:
    addi 6,6,88
    addi 7,7,1
    cmpwi 7,6,8888
    extsw 7,7
    extsw 6,6
    bne 7,.L2
    blr

Instruction A computes the inner loop counter, it is loop invariant for the
outer loop, so it can be hoisted out of the outer loop.