tree-ssa-alias.c (struct used_part): Add write_only field.

2006-01-16  Richard Guenther  <rguenther@suse.de>

	* tree-ssa-alias.c (struct used_part): Add write_only field.
	(get_or_create_used_part_for): Initialize it to true.
	(create_overlap_variables_for): Don't create structure variables
	for structures that only are written to.
	(find_used_portions): Handle MODIFY_EXPR to track whether a
	structure is only written to.

	* gcc.dg/tree-ssa/20031015-1.c: Adjust testcase.

From-SVN: r109766

gcc/ChangeLog

+2006-01-16  Richard Guenther  <rguenther@suse.de>
+
+	* tree-ssa-alias.c (struct used_part): Add write_only field.
+	(get_or_create_used_part_for): Initialize it to true.
+	(create_overlap_variables_for): Don't create structure variables
+	for structures that only are written to.
+	(find_used_portions): Handle MODIFY_EXPR to track whether a
+	structure is only written to.
+
 2006-01-16  Kazu Hirata  <kazu@codesourcery.com>
 
 	* bb-reorder.c (partition_hot_cold_basic_blocks): Make it

gcc/testsuite/ChangeLog

+2006-01-16  Richard Guenther  <rguenther@suse.de>
+
+	* gcc.dg/tree-ssa/20031015-1.c: Adjust testcase.
+
 2006-01-16  John David Anglin  <dave.anglin@nrc-cnrc.gc.ca>
 
 	PR testsuite/25777

gcc/testsuite/gcc.dg/tree-ssa/20031015-1.c

@@ -13,8 +13,6 @@ main(void)
   return 0;
 }
 
-/* The V_MUST_DEF comes from the initial assignment; the V_MAY_DEF
-   comes from the asm.  */
-/* { dg-final { scan-tree-dump-times "V_MUST_DEF" 1 "alias1" } } */
-/* { dg-final { scan-tree-dump-times "V_MAY_DEF" 1 "alias1" } } */
+/* The V_*_DEF comes from the initial assignment and the asm.  */
+/* { dg-final { scan-tree-dump-times "_DEF" 2 "alias1" } } */
 /* { dg-final { cleanup-tree-dump "alias1" } } */

gcc/tree-ssa-alias.c

@@ -2424,6 +2424,8 @@ typedef struct used_part
      variable.  Implicit uses occur when we can't tell what part we
      are referencing, and have to make conservative assumptions.  */
   bool implicit_uses;
+  /* True if the structure is only written to or taken its address.  */
+  bool write_only;
 } *used_part_t;
 
 /* An array of used_part structures, indexed by variable uid.  */
@@ -2509,6 +2511,7 @@ get_or_create_used_part_for (size_t uid)
       up->maxused = 0;
       up->explicit_uses = false;
       up->implicit_uses = false;
+      up->write_only = true;
     }
 
   return up;
@@ -2552,10 +2555,11 @@ create_overlap_variables_for (tree var)
   used_part_t up;
   size_t uid = DECL_UID (var);
 
-  if (!up_lookup (uid))
+  up = up_lookup (uid);
+  if (!up
+      || up->write_only)
     return;
 
-  up = up_lookup (uid);
   push_fields_onto_fieldstack (TREE_TYPE (var), &fieldstack, 0, NULL);
   if (VEC_length (fieldoff_s, fieldstack) != 0)
     {
@@ -2691,10 +2695,15 @@ create_overlap_variables_for (tree var)
    entire structure.  */
 
 static tree
-find_used_portions (tree *tp, int *walk_subtrees, void *data ATTRIBUTE_UNUSED)
+find_used_portions (tree *tp, int *walk_subtrees, void *lhs_p)
 {
   switch (TREE_CODE (*tp))
     {
+    case MODIFY_EXPR:
+      /* Recurse manually here to track whether the use is in the
+	 LHS of an assignment.  */
+      find_used_portions (&TREE_OPERAND (*tp, 0), walk_subtrees, tp);
+      return find_used_portions (&TREE_OPERAND (*tp, 1), walk_subtrees, NULL);
     case REALPART_EXPR:
     case IMAGPART_EXPR:
     case COMPONENT_REF:
@@ -2723,6 +2732,8 @@ find_used_portions (tree *tp, int *walk_subtrees, void *data ATTRIBUTE_UNUSED)
 	      up->explicit_uses = true;
 	    else
 	      up->implicit_uses = true;
+	    if (!lhs_p)
+	      up->write_only = false;
 	    up_insert (uid, up);
 
 	    *walk_subtrees = 0;