[Bug rtl-optimization/35371] New: Missing REG_POINTER attribute causes bad indexed load/store operand ordering

[bergner at gcc dot gnu dot org]

We fail to correctly order the operands for the indexed store within the loop
below. This seems to be caused by a missing REG_POINTER attribute, so the code
added for PR28690 doesn't have a chance of getting the ordering correct. An
interesting thing is that if we replace the global array with an "extern int
*reg_values;", then we get the ordering correct.

bergner@etna:~/gcc/tests> cat a2-loop.c 
int reg_values[1024];
void
clear_table (unsigned int n)
{
  unsigned int i;
  for (i = 0; i < n; i++)
    reg_values[i] = 0;
}

The "bad" code gen looks like (using -O2 -S):

clear_table:
        cmpwi 0,3,0
        beqlr- 0
        lis 9,reg_values@ha
        slwi 3,3,2
        la 9,reg_values@l(9)
        li 11,0
        li 0,0
        .p2align 4,,15
.L3:
        stwx 0,11,9
        addi 11,11,4
        cmpw 7,11,3
        bne+ 7,.L3
        blr

It's another question on why this isn't using an update form store and branch
on count loop, to halve the size of the loop.  The loop size is particularly
glaring when you use -O2 -funroll-loops, then we get 8 indexed stores (all with
the wrong operand order) and 8 addi's...but I guess that's for another
bugzilla.


-- 
           Summary: Missing REG_POINTER attribute causes bad indexed
                    load/store operand ordering
           Product: gcc
           Version: 4.4.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: normal
          Priority: P3
         Component: rtl-optimization
        AssignedTo: bergner 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=35371