[Bug tree-optimization/15352] [tree-ssa] missed jump threading opportunity due to lack of short circuit

law at redhat dot com gcc-bugzilla@gcc.gnu.org
Mon Feb 14 22:38:00 GMT 2005


------- Additional Comments From law at redhat dot com  2005-02-14 20:01 -------
The new jump thread selection code handles this properly.

I will note that your comments about the code we ought to be able to generate
are wrong.  The correctly optimized code should look like this:  (note the
difference in where we test c == 3.


foo (a, b, c)
{
  # BLOCK 0
  # PRED: ENTRY [100.0%]  (fallthru,exec)
  if (a_1 == 1) goto <L3>; else goto <L0>;
  # SUCC: 3 [14.9%]  (true,exec) 1 [85.1%]  (false,exec)

  # BLOCK 1
  # PRED: 0 [85.1%]  (false,exec)
<L0>:;
  if (b_3 == 2) goto <L2>; else goto <L5>;
  # SUCC: 2 [45.3%]  (true,exec) 5 [54.7%]  (false,exec)

  # BLOCK 2
  # PRED: 1 [45.3%]  (true,exec)
<L2>:;
  if (c_2 == 3) goto <L3>; else goto <L4>;
  # SUCC: 3 [48.8%]  (true,exec) 4 [51.2%]  (false,exec)

  # BLOCK 3
  # PRED: 0 [14.9%]  (true,exec) 2 [48.8%]  (true,exec)
<L3>:;
  f1 ();
  goto <bb 5> (<L5>);
  # SUCC: 5 [100.0%]  (fallthru,exec)

  # BLOCK 4
  # PRED: 2 [51.2%]  (false,exec)
<L4>:;
  f2 ();
  # SUCC: 5 [100.0%]  (fallthru,exec)

  # BLOCK 5
  # PRED: 1 [54.7%]  (false,exec) 3 [100.0%]  (fallthru,exec) 4 [100.0%] 
(fallthru,exec)
<L5>:;
  return;


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=15352



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