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

[pf3gnuchains/gcc-fork.git] / gcc / tree-ssa-alias.c

diff --git a/gcc/tree-ssa-alias.c b/gcc/tree-ssa-alias.c
index 353e7bd..5370747 100644 (file)
--- a/gcc/tree-ssa-alias.c
+++ b/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;