[Bug other/17100] New: Missed opportunity for value range optimization

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

Description:
A non-optimal code sequence is illustraded.    Duplicate using gcc 3.5 and
command line:

gcc -O3 -m64 -c test.c


Testcase:
int x;
int a[10];

void bar () {
  printf("bar\n");
}

void foo ()
{
  int i;
  int j;

  j = x;

  for (i = 0; i < 10; i++)
  {
    j += a[i];

    /* This block is successfully removed.  GCC figures
     out that 15 is out of the range of i (0-9) and
     removes the block */
    if (i == 15) bar ();

    /* This block is not removed, but could be */
    if (i == -5) bar ();
  }

}

Assembly:
.foo:
      mflr 0
      std 31,-8(1)
      li 31,0
      std 0,16(1)
      stdu 1,-128(1)
.L12:
      addi 0,31,1
      extsw 31,0
      cmpwi 7,31,9
      cmpwi 6,31,-5
      bgt- 7,.L14
.L4:
      bne+ 6,.L12
      ld 3,.LC2@toc(2)
      bl .puts
      nop
      addi 0,31,1
      extsw 31,0
      cmpwi 7,31,9
      cmpwi 6,31,-5
      ble+ 7,.L4
.L14:
      addi 1,1,128
      ld 0,16(1)
      ld 31,-8(1)
      mtlr 0
      blr



-- 
           Summary: Missed opportunity for value range optimization
           Product: gcc
           Version: 3.5.0
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P1
         Component: other
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: steinmtz at us dot ibm dot com
                CC: gcc-bugs at gcc dot gnu dot org,steinmtz at us dot ibm
                    dot com
 GCC build triplet: powerpc64-linux
  GCC host triplet: powerpc64-linux
GCC target triplet: powerpc64-linux


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17100