re PR tree-optimization/38984 (NULL pointers always considered distinct by PTA,…

re PR tree-optimization/38984 (NULL pointers always considered distinct by PTA, even with -fno-delete-null-pointer-checks)

gcc:
2009-01-28  Paolo Bonzini  <bonzini@gnu.org>

	PR tree-optimization/38984
	* tree-ssa-structalias.c (get_constraints_for_1): Do not use
	the nothing_id variable if -fno-delete-null-pointer-checks.

gcc/testsuite:
2009-01-28  Paolo Bonzini  <bonzini@gnu.org>

	PR tree-optimization/38984
	* gcc.dg/pr38984.c: New XFAILed testcase.

From-SVN: r143721

gcc/ChangeLog

+2009-01-28  Paolo Bonzini  <bonzini@gnu.org>
+
+	PR tree-optimization/38984
+	* tree-ssa-structalias.c (get_constraints_for_1): Do not use
+	the nothing_id variable if -fno-delete-null-pointer-checks.
+
 2009-01-28  Uros Bizjak  <ubizjak@gmail.com>
 
 	PR target/38988

gcc/testsuite/ChangeLog

+2009-01-28  Paolo Bonzini  <bonzini@gnu.org>
+
+	PR tree-optimization/38984
+	* gcc.dg/pr38984.c: New XFAILed testcase.
+
 2009-01-27  Paolo Carlini  <paolo.carlini@oracle.com>
 
 	PR c++/37554

gcc/testsuite/gcc.dg/pr38984.c

+/* { dg-do compile } */
+/* { dg-options "-O2 -fno-delete-null-pointer-checks -fdump-tree-optimized" }
+ * */
+
+int f(int *p)
+{
+  int a = *p;
+  int *null = 0;
+  *null = 5;
+  return *p == a;
+}
+
+/* Currently fails because of PR38985.  */
+
+/* { dg-final { scan-tree-dump-times " = \\\*p" 2 "optimized" { xfail *-*-* } } } */
+/* { dg-final { scan-tree-dump-not "return 1" "optimized" { xfail *-*-* } } } */
+/* { dg-final { cleanup-tree-dump "optimized" } } */
+
+

gcc/tree-ssa-structalias.c

@@ -3044,8 +3044,14 @@ get_constraint_for_1 (tree t, VEC (ce_s, heap) **results, bool address_p)
      happens below, since it will fall into the default case. The only
      case we know something about an integer treated like a pointer is
      when it is the NULL pointer, and then we just say it points to
-     NULL.  */
-  if (TREE_CODE (t) == INTEGER_CST
+     NULL.
+
+     Do not do that if -fno-delete-null-pointer-checks though, because
+     in that case *NULL does not fail, so it _should_ alias *anything.
+     It is not worth adding a new option or renaming the existing one,
+     since this case is relatively obscure.  */
+  if (flag_delete_null_pointer_checks
+      && TREE_CODE (t) == INTEGER_CST
       && integer_zerop (t))
     {
       temp.var = nothing_id;