[Bug rtl-optimization/17235] New: code quality regression on x86

["dann at godzilla dot ics dot uci dot edu" <gcc-bugzilla at gcc dot gnu dot org>]

Compiling 

void foo (unsigned *, unsigned *, unsigned);
unsigned *baz (unsigned) __attribute__ ((const));

struct COST
{
  unsigned *cost;

  unsigned maxWeakConstraintLevel;
};

unsigned * bar(struct COST *c)
{
  unsigned *valp;
  if(c->maxWeakConstraintLevel == 0)
    valp =0;
  else
    {
      valp = baz (4 * 33);
      foo (valp, c->cost, c->maxWeakConstraintLevel * sizeof(unsigned));
    }
  return valp;
}

with -O2 -fomit-frame-pointer on x86 generates:

bar:
        subl    $28, %esp
        movl    %edi, 24(%esp)
        movl    32(%esp), %edi
        movl    %esi, 20(%esp)
        xorl    %esi, %esi            
        movl    %ebx, 16(%esp)
        movl    4(%edi), %ebx
        testl   %ebx, %ebx
        jne     .L6                 
        movl    %esi, %eax            
        movl    16(%esp), %ebx
        movl    20(%esp), %esi
        movl    24(%esp), %edi
        addl    $28, %esp
        ret
        .p2align 4,,7
.L6:
        movl    $132, (%esp)
        call    baz
        movl    %eax, %esi     
        [snip]


Observe that stack accesses are done using mov instructions, not pop/push which
are more space efficient. 

The code generated is much bigger: mainline CVS generates 112 bytes, 
gcc-3.3.3 62 bytes and ICC 56 bytes.

Intel's compiler generates pop/push instructions for stack accesses.

-- 
           Summary: code quality regression on x86
           Product: gcc
           Version: 3.5.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: rtl-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: dann at godzilla dot ics dot uci dot edu
                CC: gcc-bugs at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17235