[Bug tree-optimization/51783] New: Missed optimization for X ==/!= (signed type) ((unsigned type) Y + Z)

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

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51783

             Bug #: 51783
           Summary: Missed optimization for X ==/!= (signed type)
                    ((unsigned type) Y + Z)
    Classification: Unclassified
           Product: gcc
           Version: 4.7.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: ktietz@gcc.gnu.org
            Target: *-*-*


Hi,

for the following example shows the missed optimization

extern int ar[256];

int foo (int x, int y, unsigned int z)
{
  int c = (int) ((unsigned int) x + z);
  return y == c;
}

We produce in 4.7 for -O2 the following optimized gimple tree:

;; Function foo (foo, funcdef_no=0, decl_uid=1601, cgraph_uid=0)

foo (int x, int y, unsigned int z)
{
  int c;
  _Bool D.2717;
  int D.2716;
  unsigned int D.2715;
  unsigned int x.0;

<bb 2>:
  x.0_2 = (unsigned int) x_1(D);
  D.2715_4 = z_3(D) + x.0_2;
  c_5 = (int) D.2715_4;
  D.2717_7 = y_6(D) == c_5;
  D.2716_8 = (int) D.2717_7;
  return D.2716_8;

}

But we could expect in this case:

;; Function foo (foo, funcdef_no=0, decl_uid=1710, cgraph_uid=0)

foo (int x, int y, unsigned int z)
{
  int D.1720;
  int c;
  _Bool D.1717;
  int D.1716;

<bb 2>:
  D.1720_10 = (int) z_3(D);
  c_5 = x_1(D) + D.1720_10;
  D.1717_7 = y_6(D) == c_5;
  D.1716_8 = (int) D.1717_7;
  return D.1716_8;

}