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Date: Mon, 30 Jul 2007 22:48:00 -0000
Subject: [Bug middle-end/32940]  New: ivopts fails to set REG_POINTER attribute on pseudo
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The ivopts pass fails to set the REG_POINTER attribute on a pseudo that is
equal to two pseudos, one of which has teh REG_POINTER attribute and the other
is just a n offset from it.  This leads us to not sort the operands on an
indexed load/store instruction causing performance problems on POWER6.

The test case used to recreate the problem is:

linux> cat > bug.c <<EOF
unsigned int *quadrant;
unsigned int
fullGtU (int i1, int n)
{
  unsigned int s1 = 0;
  for (; n >= 0; n--)
    {
      s1 = quadrant[i1];
      i1 += n;
    }
  return s1;
}
EOF

linux> /path/to/gcc -O1 -S -da bug.c

Resulting assembly:
fullGtU:
        li 0,0
        cmpwi 0,4,0
        blt 0,.L3
        lis 9,quadrant@ha
        lwz 11,quadrant@l(9)
        addi 0,4,1
        mtctr 0
        addi 0,4,-1
        cmpwi 7,0,-1
        bge+ 7,.L4
        li 0,1
        mtctr 0
.L4:
        slwi 9,3,2
        lwzx 0,9,11  <- bad operand ordering
        add 3,3,4
        addi 4,4,-1
        bdnz .L4
.L3:
        mr 3,0
        blr

Bad RTL in bug.c.127r.expand:

(insn 21 20 22 bug.c:8 (set (reg/f:SI 129)
        (plus:SI (reg:SI 128)
            (reg:SI 121 [ quadrant.0 ]))) -1 (nil))

(insn 22 21 0 bug.c:8 (set (reg/v:SI 120 [ s1 ])
        (mem:SI (reg/f:SI 129) [0 S4 A32])) -1 (nil))

Eventually, pseudo 129 )which has the REG_POINTER attribute) gets exchanged
with the (plus:SI (reg:SI 128) (reg:SI 121 [ quadrant.0 ])) and pseudo 121
doesn't have the attribute, so we end up failing to swap them.


-- 
           Summary: ivopts fails to set REG_POINTER attribute on pseudo
           Product: gcc
           Version: 4.3.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: middle-end
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: bergner at gcc dot gnu dot org
 GCC build triplet: powerpc64-linux
  GCC host triplet: powerpc64-linux
GCC target triplet: powerpc64-linux


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32940