re PR tree-optimization/48694 (possible memory hog bug)

2011-04-26  Richard Guenther  <rguenther@suse.de>

	PR middle-end/48694
	* tree.h (OEP_CONSTANT_ADDRESS_OF): New operand_equal_flag.
	* fold-const.c (operand_equal_p): For TREE_CONSTANT ADDR_EXPRs
	compare the operands with OEP_CONSTANT_ADDRESS_OF.  Treat
	trees with TREE_SIDE_EFFECTS equal when OEP_CONSTANT_ADDRESS_OF
	is set.

	* gcc.dg/torture/pr48694-1.c: New testcase.
	* gcc.dg/torture/pr48694-2.c: Likewise.

From-SVN: r172954

gcc/fold-const.c

@@ -2473,9 +2473,12 @@ operand_equal_p (const_tree arg0, const_tree arg1, unsigned int flags)
      equal if they have no side effects.  If we have two identical
      expressions with side effects that should be treated the same due
      to the only side effects being identical SAVE_EXPR's, that will
-     be detected in the recursive calls below.  */
+     be detected in the recursive calls below.
+     If we are taking an invariant address of two identical objects
+     they are necessarily equal as well.  */
   if (arg0 == arg1 && ! (flags & OEP_ONLY_CONST)
       && (TREE_CODE (arg0) == SAVE_EXPR
+	  || (flags & OEP_CONSTANT_ADDRESS_OF)
 	  || (! TREE_SIDE_EFFECTS (arg0) && ! TREE_SIDE_EFFECTS (arg1))))
     return 1;
 
@@ -2538,7 +2541,8 @@ operand_equal_p (const_tree arg0, const_tree arg1, unsigned int flags)
 
       case ADDR_EXPR:
 	return operand_equal_p (TREE_OPERAND (arg0, 0), TREE_OPERAND (arg1, 0),
-				0);
+				TREE_CONSTANT (arg0) && TREE_CONSTANT (arg1)
+				? OEP_CONSTANT_ADDRESS_OF : 0);
       default:
 	break;
       }

gcc/testsuite/ChangeLog

+2011-04-26  Richard Guenther  <rguenther@suse.de>
+
+	PR middle-end/48694
+	* gcc.dg/torture/pr48694-1.c: New testcase.
+	* gcc.dg/torture/pr48694-2.c: Likewise.
+
 2011-04-25  Paolo Carlini  <paolo.carlini@oracle.com>
 
 	* g++.dg/ext/underlying_type1.C: New.

gcc/testsuite/gcc.dg/torture/pr48694-1.c

+/* { dg-do compile } */
+
+extern volatile int g_89[5][9];
+extern int g, *gp;
+void func_64()
+{
+  int i;
+  for (i = 0; i < 1; )
+    {
+      for (g = 0; g < 1; )
+	return;
+      gp = (int *)&g_89[g][0];
+    }
+}

gcc/testsuite/gcc.dg/torture/pr48694-2.c

+/* { dg-do compile } */
+
+extern volatile int g_4[1][4];
+extern int g_7;
+void modify(int *);
+void func_2()
+{
+  int l_46 = 4;
+  if (g_7)
+    modify(&l_46);
+  else
+    {
+      int i;
+      for (i = 0; i != 5; i += 1)
+	{
+	  volatile int *vp = &g_4[0][l_46];
+	  *vp = 0;
+	}
+    }
+}

gcc/tree.h

@@ -5118,7 +5118,8 @@ extern tree fold_fma (location_t, tree, tree, tree, tree);
 enum operand_equal_flag
 {
   OEP_ONLY_CONST = 1,
-  OEP_PURE_SAME = 2
+  OEP_PURE_SAME = 2,
+  OEP_CONSTANT_ADDRESS_OF = 4
 };
 
 extern int operand_equal_p (const_tree, const_tree, unsigned int);