cfgexpand.c (add_alias_set_conflicts): Add conflicts with a variable containing…

cfgexpand.c (add_alias_set_conflicts): Add conflicts with a variable containing union type only with -fstrict-aliasing.

2011-04-20  Easwaran Raman  <eraman@google.com>

	* cfgexpand.c (add_alias_set_conflicts): Add conflicts with a variable
	containing union type only with -fstrict-aliasing.

2011-04-20  Easwaran Raman  <eraman@google.com>

	* gcc.dg/stack-layout-1.c: New test.

From-SVN: r172788

gcc/ChangeLog

+2011-04-20  Easwaran Raman  <eraman@google.com>
+
+	* cfgexpand.c (add_alias_set_conflicts): Add conflicts with a variable
+	containing union type only with -fstrict-aliasing.
+
 2011-04-20  Jim Meyering  <meyering@redhat.com>
 
 	Remove useless if-before-free tests.

gcc/cfgexpand.c

@@ -373,8 +373,9 @@ add_alias_set_conflicts (void)
 		 to elements will conflict.  In case of unions we have
 		 to be careful as type based aliasing rules may say
 		 access to the same memory does not conflict.  So play
-		 safe and add a conflict in this case.  */
-	      || contains_union)
+		 safe and add a conflict in this case when
+                 -fstrict-aliasing is used.  */
+              || (contains_union && flag_strict_aliasing))
 	    add_stack_var_conflict (i, j);
 	}
     }

gcc/testsuite/ChangeLog

+2011-04-20  Easwaran Raman  <eraman@google.com>
+
+	* gcc.dg/stack-layout-1.c: New test.
+
 2011-04-20  Daniel Jacobowitz  <dan@codesourcery.com>
 
 	* gcc.dg/vect/vect-shift-3.c, gcc.dg/vect/vect-shift-4.c: New.

gcc/testsuite/gcc.dg/stack-layout-1.c

+/* { dg-do compile } */
+/* { dg-options "-O2 -fno-strict-aliasing -fdump-rtl-expand" } */
+union U {
+  int a;
+  float b;
+};
+struct A {
+  union U u1;
+  char a[100];
+};
+void bar (struct A *);
+void foo ()
+  {
+    {
+      struct A a;
+      bar (&a);
+    }
+    {
+      struct A a;
+      bar (&a);
+    }
+  }
+
+/* { dg-final { scan-rtl-dump-times "Partition" 1 "expand" } } */
+/* { dg-final { cleanup-rtl-dump "expand" } } */