re PR tree-optimization/46398 (early FRE miscompiles simple testcase)

2010-11-10  Richard Guenther  <rguenther@suse.de>

	PR tree-optimization/46398
	* tree-ssa-sccvn.c (process_scc): Iterate for all PHIs.

	* gcc.dg/torture/pr46398.c: New testcase.

From-SVN: r166527

gcc/ChangeLog

+2010-11-10  Richard Guenther  <rguenther@suse.de>
+
+	PR tree-optimization/46398
+	* tree-ssa-sccvn.c (process_scc): Iterate for all PHIs.
+
 2010-11-10  Joern Rennecke  <amylaar@spamcop.net>
 
 	PR target/44760

gcc/testsuite/ChangeLog

+2010-11-10  Richard Guenther  <rguenther@suse.de>
+
+	PR tree-optimization/46398
+	* gcc.dg/torture/pr46398.c: New testcase.
+
 2010-11-09  Jerry DeLisle  <jvdelisle@gcc.gnu.org>
 
 	* gfortran.dg/open_dev_null.f90: New test.
 
 2010-11-09   Jan Hubicka  <jh@suse.cz>
 
-	* testsuite/gcc.target/i386/recip-vec-sqrtf-avx.c: Update for loop unrolling.
+	* testsuite/gcc.target/i386/recip-vec-sqrtf-avx.c: Update for loop
+	unrolling.
 
 2010-11-09  Joseph Myers  <joseph@codesourcery.com>
 

gcc/testsuite/gcc.dg/torture/pr46398.c

+/* { dg-do run } */
+
+int __attribute__((noinline))
+test (int token)
+{
+  int done = 0;
+  int virtual_p = 0;
+  while (!done)
+    {
+      if (token == 42)
+	virtual_p = 1;
+      else
+	done = 1;
+    }
+  return virtual_p;
+}
+extern void abort (void);
+int
+main()
+{
+  if (test (0) != 0)
+    abort ();
+  return 0;
+}

gcc/tree-ssa-sccvn.c

@@ -3108,9 +3108,20 @@ process_scc (VEC (tree, heap) *scc)
   if (VEC_length (tree, scc) == 1)
     {
       tree use = VEC_index (tree, scc, 0);
-      if (!VN_INFO (use)->use_processed)
-	visit_use (use);
-      return;
+      if (VN_INFO (use)->use_processed)
+	return;
+      /* We need to make sure it doesn't form a cycle itself, which can
+	 happen for self-referential PHI nodes.  In that case we would
+	 end up inserting an expression with VN_TOP operands into the
+	 valid table which makes us derive bogus equivalences later.
+	 The cheapest way to check this is to assume it for all PHI nodes.  */
+      if (gimple_code (SSA_NAME_DEF_STMT (use)) == GIMPLE_PHI)
+	/* Fallthru to iteration.  */ ;
+      else
+	{
+	  visit_use (use);
+	  return;
+	}
     }
 
   /* Iterate over the SCC with the optimistic table until it stops