kill stores to never read entities

[r22150]

diff --git a/ir/opt/ldstopt.c b/ir/opt/ldstopt.c
index dd8e5a5..f4ba1f9 100644 (file)
--- a/ir/opt/ldstopt.c
+++ b/ir/opt/ldstopt.c
@@ -1352,18 +1352,61 @@ static unsigned follow_Mem_chain_for_Store(ir_node *store, ir_node *curr) {
        return res;
 }  /* follow_Mem_chain_for_Store */
 
+/** find entity used as base for an address calculation */
+static ir_entity *find_entity(ir_node *ptr)
+{
+       switch(get_irn_opcode(ptr)) {
+       case iro_SymConst:
+               return get_SymConst_entity(ptr);
+       case iro_Sel: {
+               ir_node *pred = get_Sel_ptr(ptr);
+               if (get_irg_frame(get_irn_irg(ptr)) == pred)
+                       return get_Sel_entity(ptr);
+
+               return find_entity(pred);
+       }
+       case iro_Sub:
+       case iro_Add: {
+               ir_node *left = get_binop_left(ptr);
+               ir_node *right;
+               if (mode_is_reference(get_irn_mode(left)))
+                       return find_entity(left);
+               right = get_binop_right(ptr);
+               if (mode_is_reference(get_irn_mode(right)))
+                       return find_entity(right);
+               return NULL;
+       }
+       default:
+               return NULL;
+       }
+}
+
 /**
  * optimize a Store
  *
  * @param store  the Store node
  */
 static unsigned optimize_store(ir_node *store) {
-       ir_node *ptr, *mem;
+       ir_node   *ptr;
+       ir_node   *mem;
+       ir_entity *entity;
 
        if (get_Store_volatility(store) == volatility_is_volatile)
                return 0;
 
-       ptr = get_Store_ptr(store);
+       ptr    = get_Store_ptr(store);
+       entity = find_entity(ptr);
+
+       /* a store to an entity which is never read is unnecessary */
+       if (!(get_entity_usage(entity) & ir_usage_read)) {
+               ldst_info_t *info = get_irn_link(store);
+               if (info->projs[pn_Store_X_except] == NULL) {
+                       exchange(info->projs[pn_Store_M], get_Store_mem(store));
+                       kill_node(store);
+                       reduce_adr_usage(ptr);
+                       return DF_CHANGED;
+               }
+       }
 
        /* Check, if the address of this Store is used more than once.
         * If not, this Store cannot be removed in any case. */