re PR tree-optimization/47391 (read from const volatile incorrectly eliminated)

	PR tree-optimization/47391
	* varpool.c (const_value_known_p): Return false if
	decl is volatile.

	* gcc.dg/pr47391.c: New test.

From-SVN: r169084

gcc/ChangeLog

@@ -3,6 +3,10 @@
 	* tree-ssa-live.c (remove_unused_scope_block_p): Don't remove
 	DECL_IGNORED_P non-reg vars if they are used.
 
+	PR tree-optimization/47391
+	* varpool.c (const_value_known_p): Return false if
+	decl is volatile.
+
 2011-01-21  Kai Tietz  <kai.tietz@onevision.com>
 
 	PR bootstrap/47215

gcc/testsuite/ChangeLog

+2011-01-21  Jakub Jelinek  <jakub@redhat.com>
+
+	PR tree-optimization/47391
+	* gcc.dg/pr47391.c: New test.
+
 2011-01-21  Rainer Orth  <ro@CeBiTec.Uni-Bielefeld.DE>
 
 	* g++.dg/template/char1.C: Use signed char.

gcc/testsuite/gcc.dg/pr47391.c

+/* PR tree-optimization/47391 */
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-optimized" } */
+
+const volatile int v = 1;
+int i = 0;
+
+void
+foo (void)
+{
+  i = v;
+}
+
+int
+main (void)
+{
+  foo ();
+  return 0;
+}
+
+/* { dg-final { scan-tree-dump-not "i = 1;" "optimized" } } */
+/* { dg-final { cleanup-tree-dump "optimized" } } */

gcc/varpool.c

 /* Callgraph handling code.
-   Copyright (C) 2003, 2004, 2005, 2006, 2007, 2008, 2010
+   Copyright (C) 2003, 2004, 2005, 2006, 2007, 2008, 2010, 2011
    Free Software Foundation, Inc.
    Contributed by Jan Hubicka
 
@@ -370,7 +370,7 @@ const_value_known_p (tree decl)
 
   gcc_assert (TREE_CODE (decl) == VAR_DECL);
 
-  if (!TREE_READONLY (decl))
+  if (!TREE_READONLY (decl) || TREE_THIS_VOLATILE (decl))
     return false;
 
   /* Gimplifier takes away constructors of local vars  */