[Bug tree-optimization/16179] New: useless copies not optimized away

[rguenth at tat dot physik dot uni-tuebingen dot de]

The following functions do not produce identical results
(g++-3.5 (GCC) 3.5.0 20040618 (experimental), -O2)

extern void bar(void);

int foo(const int &f)
{
        const int a = f;
        int c = a;
        bar();
        c = a;
        return c;
}

int foo2(const int &f)
{
        int c = f;
        bar();
        c = f;
        return c;
}

optimized tree-dump (asm contains the useless store to a, too,
but the tree-optimizers should catch that):

;; Function int foo(const int&) (_Z3fooRKi)

int foo(const int&) (f)
{
  int c;
  const int a;
  int T.0;

<bb 0>:
  a = *f;
  bar ();
  return a;

}



;; Function int foo2(const int&) (_Z4foo2RKi)

int foo2(const int&) (f)
{
  int c;
  int T.1;

<bb 0>:
  bar ();
  return *f;

}

-- 
           Summary: useless copies not optimized away
           Product: gcc
           Version: 3.5.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: tree-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: rguenth at tat dot physik dot uni-tuebingen dot de
                CC: gcc-bugs at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=16179