re PR tree-optimization/56661 (Incorrect code with -O1 -ftree-pre)

2013-03-20  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/56661
	* tree-ssa-sccvn.c (visit_use): Only value-number calls if
	the result does not have to be distinct.

	* gcc.dg/torture/pr56661.c: New testcase.

From-SVN: r196825

gcc/ChangeLog

 2013-03-20  Richard Biener  <rguenther@suse.de>
 
+	PR tree-optimization/56661
+	* tree-ssa-sccvn.c (visit_use): Only value-number calls if
+	the result does not have to be distinct.
+
+2013-03-20  Richard Biener  <rguenther@suse.de>
+
 	* tree-inline.c (copy_tree_body_r): Sync MEM_REF code with
 	remap_gimple_op_r.
 

gcc/testsuite/ChangeLog

+2013-03-20  Richard Biener  <rguenther@suse.de>
+
+	PR tree-optimization/56661
+	* gcc.dg/torture/pr56661.c: New testcase.
+
 2013-03-20  Bill Schmidt  <wschmidt@linux.vnet.ibm.com>
 
 	PR rtl-optimization/56605

gcc/testsuite/gcc.dg/torture/pr56661.c

+/* { dg-do run } */
+
+__attribute__((noinline, noclone)) void
+bar (int *b)
+{
+  b[0] = b[1] = b[2] = 1;
+}
+
+__attribute__((noinline, noclone)) int
+baz (int x)
+{
+  if (x != 1)
+    __builtin_abort ();
+}
+
+void
+foo (int x)
+{
+  if (x == 0)
+    {
+      int *b = __builtin_malloc (3 * sizeof (int));
+      while (b[0])
+	;
+    }
+  else if (x == 1)
+    {
+      int i, j;
+      int *b = __builtin_malloc (3 * sizeof (int));
+      for (i = 0; i < 2; i++)
+	{
+	  bar (b);
+	  for (j = 0; j < 3; ++j)
+	    baz (b[j]);
+	  baz (b[0]);
+	}
+    }
+}
+
+int
+main ()
+{
+  int x = 1;
+  asm volatile ("" : "+r" (x));
+  foo (x);
+  return 0;
+}

gcc/tree-ssa-sccvn.c

@@ -3506,8 +3506,13 @@ visit_use (tree use)
 		     We can value number 2 calls to the same function with the
 		     same vuse and the same operands which are not subsequent
 		     the same, because there is no code in the program that can
-		     compare the 2 values.  */
-		  || gimple_vdef (stmt)))
+		     compare the 2 values...  */
+		  || (gimple_vdef (stmt)
+		      /* ... unless the call returns a pointer which does
+		         not alias with anything else.  In which case the
+			 information that the values are distinct are encoded
+			 in the IL.  */
+		      && !(gimple_call_return_flags (stmt) & ERF_NOALIAS))))
 	    changed = visit_reference_op_call (lhs, stmt);
 	  else
 	    changed = defs_to_varying (stmt);