- ldst_info_t *info = get_irn_link(load);
- ir_mode *load_mode = get_Load_mode(load);
- ir_node *pred, *mem, *ptr;
- entity *ent;
- int res = 0;
-
- /* the address of the load to be optimized */
- ptr = get_Load_ptr(load);
-
- /*
- * Check if we can remove the exception form a Load:
- * this can be done, if the address is from an Sel(Alloc) and
- * the Sel type is a subtype of the alloc type.
- *
- * This optimizes some often used OO constructs,
- * like x = new O; x->t;
- */
- if (info->projs[pn_Load_X_except]) {
- if (get_irn_op(ptr) == op_Sel) {
- ir_node *mem = get_Sel_mem(ptr);
-
- if (get_irn_op(mem) == op_Alloc) {
- /* ok, check the types */
- entity *ent = get_Sel_entity(ptr);
- type *s_type = get_entity_type(ent);
- type *a_type = get_Alloc_type(mem);
-
- if (is_subclass_of(s_type, a_type)) {
- /* ok, condition met: there can't be an exception because
- * alloc guarantees that enough memory was allocated */
-
- exchange(info->projs[pn_Load_X_except], new_Bad());
- info->projs[pn_Load_X_except] = NULL;
- }
- }
- }
- else if (get_irn_op(ptr) == op_Alloc) {
- /* simple case: a direct load after an Alloc. Firm Alloc throw
- * an exception in case of out-of-memory. So, there is no way for an
- * exception in this load.
- * This code is constructed by the "exception lowering" in the Jack compiler.
- */
- exchange(info->projs[pn_Load_X_except], new_Bad());
- info->projs[pn_Load_X_except] = NULL;
- }
- }
-
- /* do NOT touch volatile loads for now */
- if (get_Load_volatility(load) == volatility_is_volatile)
- return 0;
-
- if (! info->projs[pn_Load_res] && ! info->projs[pn_Load_X_except]) {
- /* a Load which value is neither used nor exception checked, remove it */
- mem = get_Load_mem(load);
- exchange(info->projs[pn_Load_M], mem);
-
- return 1;
- }
-
- /* the mem of the Load. Must still be returned after optimization */
- mem = get_Load_mem(load);
-
- /* check if we can determine the entity that will be loaded */
- ent = find_constant_entity(ptr);
- if (ent) {
- if ((allocation_static == get_entity_allocation(ent)) &&
- (visibility_external_allocated != get_entity_visibility(ent))) {
- /* a static allocation that is not external: there should be NO exception
- * when loading. */
-
- /* no exception, clear the info field as it might be checked later again */
- if (info->projs[pn_Load_X_except]) {
- exchange(info->projs[pn_Load_X_except], new_Bad());
- info->projs[pn_Load_X_except] = NULL;
- }
-
- if (variability_constant == get_entity_variability(ent)
- && is_atomic_entity(ent)) { /* Might not be atomic after
- lowering of Sels. In this
- case we could also load, but
- it's more complicated. */
- /* more simpler case: we load the content of a constant value:
- * replace it by the constant itself
- */
-
- /* no memory */
- if (info->projs[pn_Load_M])
- exchange(info->projs[pn_Load_M], mem);
-
- /* no result :-) */
- if (info->projs[pn_Load_res]) {
- if (is_atomic_entity(ent)) {
- ir_node *c = copy_const_value(get_atomic_ent_value(ent));
-
- DBG_OPT_RC(load, c);
- exchange(info->projs[pn_Load_res], c);
-
- return 1;
- }
- }
- }
- else if (variability_constant == get_entity_variability(ent)) {
- printf(">>>>>>>>>>>>> Found access to constant entity %s in function %s\n", get_entity_name(ent),
- get_entity_name(get_irg_entity(current_ir_graph)));
- }
-
- /* we changed the irg, but try further */
- res = 1;
- }
- }
-
- /* Check, if the address of this load is used more than once.
- * If not, this load cannot be removed in any case. */
- if (get_irn_out_n(ptr) <= 1)
- return 0;
-
- /* follow the memory chain as long as there are only Loads */
- for (pred = skip_Proj(mem); ; pred = skip_Proj(get_Load_mem(pred))) {
-
- /*
- * BEWARE: one might think that checking the modes is useless, because
- * if the pointers are identical, they refer to the same object.
- * This is only true in strong typed languages, not is C were the following
- * is possible a = *(type1 *)p; b = *(type2 *)p ...
- */
-
- if (get_irn_op(pred) == op_Store && get_Store_ptr(pred) == ptr &&
- get_irn_mode(get_Store_value(pred)) == load_mode) {
- ldst_info_t *pred_info = get_irn_link(pred);
-
- /*
- * a Load immediately after a Store -- a read after write.
- * We may remove the Load, if both Load & Store does not have an exception handler
- * OR they are in the same block. In the latter case the Load cannot
- * throw an exception when the previous Store was quiet.
- *
- * Why we need to check for Store Exc? If the Store cannot be executed (ROM)
- * the exception handler might simply jump into the load block :-(
- * We could make it a little bit better if we would know that the exception
- * handler of the Store jumps directly to the end...
- */
- if ((!pred_info->projs[pn_Store_X_except] && !info->projs[pn_Load_X_except]) ||
- get_nodes_block(load) == get_nodes_block(pred)) {
- DBG_OPT_RAW(load, pred);
- exchange( info->projs[pn_Load_res], get_Store_value(pred) );
-
- if (info->projs[pn_Load_M])
- exchange(info->projs[pn_Load_M], mem);
-
- /* no exception */
- if (info->projs[pn_Load_X_except])
- exchange( info->projs[pn_Load_X_except], new_Bad());
- return 1;
- }
- }
- else if (get_irn_op(pred) == op_Load && get_Load_ptr(pred) == ptr &&
- get_Load_mode(pred) == load_mode) {
- /*
- * a Load after a Load -- a read after read.
- * We may remove the second Load, if it does not have an exception handler
- * OR they are in the same block. In the later case the Load cannot
- * throw an exception when the previous Load was quiet.
- *
- * Here, there is no need to check if the previos Load has an exception hander because
- * they would have exact the same exception...
- */
- if (! info->projs[pn_Load_X_except] || get_nodes_block(load) == get_nodes_block(pred)) {
- ldst_info_t *pred_info = get_irn_link(pred);
-
- DBG_OPT_RAR(load, pred);
-
- if (pred_info->projs[pn_Load_res]) {
- /* we need a data proj from the previous load for this optimization */
- exchange( info->projs[pn_Load_res], pred_info->projs[pn_Load_res] );
- if (info->projs[pn_Load_M])
- exchange(info->projs[pn_Load_M], mem);
- }
- else {
- if (info->projs[pn_Load_res]) {
- set_Proj_pred(info->projs[pn_Load_res], pred);
- set_nodes_block(info->projs[pn_Load_res], get_nodes_block(pred));
- }
- if (info->projs[pn_Load_M]) {
- /* Actually, this if should not be necessary. Construct the Loads
- properly!!! */
- exchange(info->projs[pn_Load_M], mem);
- }
- }
-
- /* no exception */
- if (info->projs[pn_Load_X_except])
- exchange(info->projs[pn_Load_X_except], new_Bad());
-
- return 1;
- }
- }
-
- /* follow only Load chains */
- if (get_irn_op(pred) != op_Load)
- break;
- }
- return res;
-}
+ return get_mode_size_bits(new_mode) >= get_mode_size_bits(old_mode);
+} /* is_completely_overwritten */
+
+/**
+ * follow the memory chain as long as there are only Loads and alias free Stores.
+ *
+ * INC_MASTER() must be called before dive into
+ */
+static unsigned follow_Mem_chain_for_Store(ir_node *store, ir_node *curr) {
+ unsigned res = 0;
+ ldst_info_t *info = get_irn_link(store);
+ ir_node *pred;
+ ir_node *ptr = get_Store_ptr(store);
+ ir_node *mem = get_Store_mem(store);
+ ir_node *value = get_Store_value(store);
+ ir_mode *mode = get_irn_mode(value);
+ ir_node *block = get_nodes_block(store);
+
+ for (pred = curr; pred != store;) {
+ ldst_info_t *pred_info = get_irn_link(pred);
+
+ /*
+ * BEWARE: one might think that checking the modes is useless, because
+ * if the pointers are identical, they refer to the same object.
+ * This is only true in strong typed languages, not is C were the following
+ * is possible *(ir_type1 *)p = a; *(ir_type2 *)p = b ...
+ * However, if the mode that is written have a bigger or equal size the the old
+ * one, the old value is completely overwritten and can be killed ...
+ */
+ if (get_irn_op(pred) == op_Store && get_Store_ptr(pred) == ptr &&
+ get_nodes_block(pred) == block &&
+ is_completely_overwritten(get_irn_mode(get_Store_value(pred)), mode)) {
+ /*
+ * a Store after a Store in the same block -- a write after write.
+ * We may remove the first Store, if it does not have an exception handler.
+ *
+ * TODO: What, if both have the same exception handler ???
+ */
+ if (get_Store_volatility(pred) != volatility_is_volatile && !pred_info->projs[pn_Store_X_except]) {
+ DBG_OPT_WAW(pred, store);
+ exchange( pred_info->projs[pn_Store_M], get_Store_mem(pred) );
+ exchange(pred, new_Bad());
+ reduce_adr_usage(ptr);
+ return DF_CHANGED;
+ }
+ } else if (get_irn_op(pred) == op_Load && get_Load_ptr(pred) == ptr &&
+ value == pred_info->projs[pn_Load_res]) {
+ /*
+ * a Store of a value after a Load -- a write after read.
+ * We may remove the second Store, if it does not have an exception handler.
+ */
+ if (! info->projs[pn_Store_X_except]) {
+ DBG_OPT_WAR(store, pred);
+ exchange( info->projs[pn_Store_M], mem );
+ exchange(store, new_Bad());
+ reduce_adr_usage(ptr);
+ return DF_CHANGED;
+ }
+ }
+
+ if (get_irn_op(pred) == op_Store) {
+ /* check if we can pass thru this store */
+ ir_alias_relation rel = get_alias_relation(
+ current_ir_graph,
+ get_Store_ptr(pred),
+ get_irn_mode(get_Store_value(pred)),
+ ptr, mode);
+ /* if the might be an alias, we cannot pass this Store */
+ if (rel != no_alias)
+ break;
+ pred = skip_Proj(get_Store_mem(pred));
+ } else if (get_irn_op(pred) == op_Load) {
+ pred = skip_Proj(get_Load_mem(pred));
+ } else {
+ /* follow only Load chains */
+ break;
+ }
+
+ /* check for cycles */
+ if (NODE_VISITED(pred_info))
+ break;
+ MARK_NODE(pred_info);
+ }
+
+ if (get_irn_op(pred) == op_Sync) {
+ int i;
+
+ /* handle all Sync predecessors */
+ for (i = get_Sync_n_preds(pred) - 1; i >= 0; --i) {
+ res |= follow_Mem_chain_for_Store(store, skip_Proj(get_Sync_pred(pred, i)));
+ if (res)
+ break;
+ }
+ }
+ return res;
+} /* follow_Mem_chain_for_Store */