re PR tree-optimization/17252 (not marking char types as aliasing anything)

	PR tree-optimization/17252
	* tree-ssa-alias.c (may_alias_p): Don't assume that a
	pointer may not point to itself when using relaxed
	aliasing rules.

testsuite/ChangeLog

	PR tree-optimization/17252
	* gcc.c-torture/execute/pr17252.c: New test.

From-SVN: r87529

gcc/ChangeLog

+2004-09-14  Diego Novillo  <dnovillo@redhat.com>
+
+	PR tree-optimization/17252
+	* tree-ssa-alias.c (may_alias_p): Don't assume that a
+	pointer may not point to itself when using relaxed
+	aliasing rules.
+
 2004-09-14  Richard Henderson  <rth@redhat.com>
 
 	PR middle-end/17397

gcc/testsuite/ChangeLog

+2004-09-14  Diego Novillo  <dnovillo@redhat.com>
+
+	PR tree-optimization/17252
+	* gcc.c-torture/execute/pr17252.c: New test.
+
 2004-09-14  Andrew Pinski  <apinski@apple.com>
 
 	* g++.dg/tree-ssa/pointer-reference-alias.C: New test.

gcc/testsuite/gcc.c-torture/execute/pr17252.c

+/* PR 17252.  When a char * pointer P takes its own address, storing
+   into *P changes P itself.  */
+
+char *a;
+
+main ()
+{
+  int i;
+
+  /* Make 'a' point to itself.  */
+  a = (char *)&a;
+
+  /* Assign NULL to 'a' byte by byte.  */
+  for (i = 0; i < sizeof(char *); i++)
+    a[i] = 0;
+
+  /* If a's memory tag does not contain 'a' in its alias set, we will
+     think that this predicate is superfluous and change it to
+     'if (1)'.  */
+  if (a == (char *)&a)
+    abort ();
+
+  return 0;
+}

gcc/tree-ssa-alias.c

@@ -1558,7 +1558,8 @@ may_alias_p (tree ptr, HOST_WIDE_INT mem_alias_set,
      for PTR's alias set here, not its pointed-to type.  We also can't
      do this check with relaxed aliasing enabled.  */
   if (POINTER_TYPE_P (TREE_TYPE (var))
-      && var_alias_set != 0)
+      && var_alias_set != 0
+      && mem_alias_set != 0)
     {
       HOST_WIDE_INT ptr_alias_set = get_alias_set (ptr);
       if (ptr_alias_set == var_alias_set)