re PR middle-end/33330 (Wrong alias for accessing scalar through array)

2007-09-07  Richard Guenther  <rguenther@suse.de>

	PR middle-end/33330
	* tree-ssa-operands.c (access_can_touch_variable): An access
	of the form (*p)[0] can touch a variable of same size.

From-SVN: r128240

gcc/ChangeLog

+2007-09-07  Richard Guenther  <rguenther@suse.de>
+
+	PR middle-end/33330
+	* tree-ssa-operands.c (access_can_touch_variable): An access
+	of the form (*p)[0] can touch a variable of same size.
+
 2007-09-07  Jan Hubicka  <jh@suse.cz>
 
 	* passes.c (init_optimization_passes): Add simple dce and addressable

gcc/tree-ssa-operands.c

@@ -1292,6 +1292,15 @@ access_can_touch_variable (tree ref, tree alias, HOST_WIDE_INT offset,
      }
      To implement this, we just punt on accesses through union
      pointers entirely.
+
+     Another case we have to allow is accessing a variable
+     through an array access at offset zero.  This happens from
+     code generated by the fortran frontend like
+
+     char[1:1] & my_char_ref;
+     char my_char;
+     my_char_ref_1 = (char[1:1] &) &my_char;
+     D.874_2 = (*my_char_ref_1)[1]{lb: 1 sz: 1};
   */
   else if (ref 
 	   && flag_strict_aliasing
@@ -1300,6 +1309,14 @@ access_can_touch_variable (tree ref, tree alias, HOST_WIDE_INT offset,
 	   && base
 	   && (TREE_CODE (base) != INDIRECT_REF
 	       || TREE_CODE (TREE_TYPE (base)) != UNION_TYPE)
+	   && (TREE_CODE (base) != INDIRECT_REF
+	       || TREE_CODE (ref) != ARRAY_REF
+	       || offset != 0
+	       || (DECL_SIZE (alias)
+		   && TREE_CODE (DECL_SIZE (alias)) == INTEGER_CST
+		   && size != -1
+		   && (unsigned HOST_WIDE_INT)size
+		      != TREE_INT_CST_LOW (DECL_SIZE (alias))))
 	   && !AGGREGATE_TYPE_P (TREE_TYPE (alias))
 	   && TREE_CODE (TREE_TYPE (alias)) != COMPLEX_TYPE
 	   && !var_ann (alias)->is_heapvar