re PR tree-optimization/48228 (incorrect signed overflow warning when only 0 and 1 are used)

2011-03-22  Richard Guenther  <rguenther@suse.de>

	PR tree-optimization/48228
	* tree-vrp.c (vrp_visit_phi_node): Do not stop propagating
	for single-arg PHIs.

	* gcc.dg/Wstrict-overflow-23.c: New testcase.

From-SVN: r171287

gcc/ChangeLog

@@ -1,3 +1,9 @@
+2011-03-22  Richard Guenther  <rguenther@suse.de>
+
+	PR tree-optimization/48228
+	* tree-vrp.c (vrp_visit_phi_node): Do not stop propagating
+	for single-arg PHIs.
+
 2011-03-22  Andrey Belevantsev  <abel@ispras.ru>
 
 	PR rtl-optimization/48143

gcc/testsuite/ChangeLog

@@ -1,3 +1,8 @@
+2011-03-22  Richard Guenther  <rguenther@suse.de>
+
+	PR tree-optimization/48228
+	* gcc.dg/Wstrict-overflow-23.c: New testcase.
+
 2011-03-21  Jack Howarth  <howarth@bromo.med.uc.edu>
 
 	* lib/prune.exp (prune_gcc_output): Prune "could not create

gcc/testsuite/gcc.dg/Wstrict-overflow-23.c

@@ -0,0 +1,31 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -Wstrict-overflow" } */
+
+unsigned int
+do_scrolling (unsigned int window_size, unsigned int writecost)
+{
+  unsigned int i = window_size;
+
+  int terminal_window_p = 0;
+  unsigned int queue = 0;
+
+  for (i = window_size; i; i--)
+    {
+      if (writecost < i)
+    ++queue;
+      else if (writecost & 1)
+    terminal_window_p = 1;
+    }
+
+  if (queue > 0)
+    {
+      if (!terminal_window_p)
+    {
+      terminal_window_p = 1;
+    }
+    }
+
+  if (terminal_window_p)
+    return 100;
+  return 0;
+}

gcc/tree-vrp.c

@@ -6619,6 +6619,7 @@ vrp_visit_phi_node (gimple phi)
      edge; this helps us avoid an overflow infinity for conditionals
      which are not in a loop.  */
   if (edges > 0
+      && gimple_phi_num_args (phi) > 1
       && edges == old_edges)
     {
       int cmp_min = compare_values (lhs_vr->min, vr_result.min);