[tree-ssa] Optimizing if statements

[Steven Bosscher]

Consider this simple function,

void
foo (int bar)
{
  int boz = 0;

  if (bar > 0)
    boz = bar;

  if (boz > 0)
    printf ("Yup!\n");
}

Compiled with -O2, t.c.t14.optimized looks like this:

;; Function foo (foo)

foo (bar)
{
  int s;
  extern  printf;

  s = 0 ;
  if (bar > 0)
    {
      s = bar
    };
  if (s > 0)
    {
      printf ((const char *)(char *)"Yup!\n")
    }
}


Shouldn't tree-ssa be able to optimize away one of the
"if" statements here (since (s > 0) iff (bar > 0))?
Eventually, one of the RTL optimizers takes care of it,
but it would be nice if it could be done at the tree
level.

Gr.
Steven