[PATCH] Fix PR56426

Marek Polacek polacek@redhat.com
Mon Feb 25 19:53:00 GMT 2013


This fixes PR56426.  We were ICEing during the loop pipeline,
because copyprop changed an irreducible region into a reducible - thus
the number_of_loops grew.  Firstly, in tree_ssa_loop_init, number_of_loops
was == 1, which means we didn't initialize SCEV.  But then later on, in
tree_ssa_loop_bounds, the number_of_loops was 2, thus we called
estimate_numbers_of_iterations.  Oops.  So fixed by always initializing
SCEV in the loop initialization on the tree level.

Another approach would be to skip the whole loop pipeline - but then
we'd miss e.g. the BB vectorization.

Richi: no, I didn't forget to change the TODO_update_ssa to 0, but that 
ICEd pretty soon when building gcc :(.

Regtested/bootstrapped on x86_64-linux, ok for trunk?

2013-02-25  Marek Polacek  <polacek@redhat.com>

	PR tree-optimization/56426
	* tree-ssa-loop.c (tree_ssa_loop_init): Always call
	scev_initialize.

	* gcc.dg/pr56436.c: New test.

--- gcc/tree-ssa-loop.c.mp	2013-02-25 13:06:47.212132327 +0100
+++ gcc/tree-ssa-loop.c	2013-02-25 20:09:30.668978936 +0100
@@ -70,10 +70,13 @@ tree_ssa_loop_init (void)
 		       | LOOPS_HAVE_RECORDED_EXITS);
   rewrite_into_loop_closed_ssa (NULL, TODO_update_ssa);
 
+  /* We might discover new loops, e.g. when turning irreducible
+     regions into reducible.  */
+  scev_initialize ();
+
   if (number_of_loops () <= 1)
     return 0;
 
-  scev_initialize ();
   return 0;
 }
 
--- gcc/testsuite/gcc.dg/pr56436.c.mp	2013-02-25 20:19:10.213561026 +0100
+++ gcc/testsuite/gcc.dg/pr56436.c	2013-02-25 20:19:02.944541180 +0100
@@ -0,0 +1,22 @@
+/* PR tree-optimization/56426 */
+/* { dg-do compile } */
+/* { dg-options "-O2" } */
+
+int a, *c;
+
+void
+f (void)
+{
+  int b = 0;
+
+  for (a = 0;; a++)
+    if (--b)
+      {
+	if (a)
+	lbl:
+	  a++;
+
+	c = &b;
+	goto lbl;
+      }
+}

	Marek



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