[Bug optimization/14016] New: [tree-ssa] User variable get eliminated, only to be replaced with compiler generated ones

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

For:
void test55 (void)
{
  int u;
  int XXX, YYY;
  XXX = foo ();
  YYY = bar ();
  if (XXX != 5 && YYY)
    {
      u = XXX + 22;
      if (u != 27)
        baz ();
    }
}

The .optimized dump looks like:
;; Function test55 (test55)

test55 ()
{
  int T.1;
  int T.0;

<bb 0>:
  T.0 = foo ();
  T.1 = bar ();
  if (T.0 != 5 && T.1 != 0) goto <L0>; else goto <L2>;

<L0>:;
  if (T.0 + 22 != 27) goto <L1>; else goto <L2>;

<L1>:;
  baz ();

<L2>:;
<L3>:;
  return;

}

The XXX and YYY variables have been replaced with the compiler generated T.0 
and T.1

T.0 and T.1 are created in .generic
  T.0 = foo ();
  XXX = T.0;
  T.1 = bar ();
  YYY = T.1;
  T.2 = XXX != 5;
  T.3 = YYY != 0;
  T.4 = T.2 && T.3;

in .dom1 XXX and YYY in the T.2 and T.3 assignments are replaces with T.0 and
T.1

  T.0_1 = foo ();
  XXX_2 = T.0_1;
  T.1_3 = bar ();
  YYY_4 = T.1_3;
  T.2_5 = T.0_1 != 5;
  T.3_6 = T.1_3 != 0;

and finally dce2 eliminates XXX and YYY as they are not used anymore.

-- 
           Summary: [tree-ssa] User variable get eliminated, only to be
                    replaced with compiler generated ones
           Product: gcc
           Version: tree-ssa
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: 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=14016