[Bug tree-optimization/39052] New: writing arrays twice not optimized

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

In the test case below, both stores are done.

The compiler chould eliminate the first loop completely.

$ cat a.c
void foo(int *a, int n)
{
   int i;

   for (i=0; i<n; i++)
      a[i] = 0;

   for (i=0; i<n; i++)
      a[i] = 1;
}
$ gcc -O3 -S a.c
$ cat a.s
        .file   "a.c"
        .text
        .p2align 4,,15
.globl foo
        .type   foo, @function
foo:
        pushl   %ebp
        movl    %esp, %ebp
        movl    12(%ebp), %edx
        movl    8(%ebp), %ecx
        testl   %edx, %edx
        jle     .L5
        xorl    %eax, %eax
        .p2align 4,,7
        .p2align 3
.L3:
        movl    $0, (%ecx,%eax,4)
        addl    $1, %eax
        cmpl    %edx, %eax
        jne     .L3
        xorl    %eax, %eax
        .p2align 4,,7
        .p2align 3
.L4:
        movl    $1, (%ecx,%eax,4)
        addl    $1, %eax
        cmpl    %edx, %eax
        jne     .L4
.L5:
        popl    %ebp
        ret
        .size   foo, .-foo
        .ident  "GCC: (GNU) 4.4.0 20090124 (experimental)"
        .section        .note.GNU-stack,"",@progbits


-- 
           Summary: writing arrays twice not optimized
           Product: gcc
           Version: 4.4.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: normal
          Priority: P3
         Component: tree-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: tkoenig at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39052