Implement tracking and optimizations of packed arrays

src/hydrogen.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 1691 matching lines @@
     bool hoisted = false;
     if (instr->CheckFlag(HValue::kUseGVN)) {
       TRACE_GVN_4("Checking instruction %d (%s) %s. Loop %s\n",
                   instr->id(),
                   instr->Mnemonic(),
                   *GetGVNFlagsString(instr->gvn_flags()),
                   *GetGVNFlagsString(loop_kills));
       bool can_hoist = !instr->gvn_flags().ContainsAnyOf(depends_flags);
       if (instr->IsTransitionElementsKind()) {
         // It's possible to hoist transitions out of a loop as long as the
-        // hoisting wouldn't move the transition past a DependsOn of one of it's
-        // changes or any instructions that might change an objects map or
-        // elements contents.
-        GVNFlagSet changes = instr->ChangesFlags();
+        // hoisting wouldn't move the transition past an instruction that has a
+        // DependsOn flag for anything it changes.
         GVNFlagSet hoist_depends_blockers =
-            HValue::ConvertChangesToDependsFlags(changes);
-        // In addition to not hoisting transitions above other instructions that
-        // change dependencies that the transition changes, it must not be
-        // hoisted above map changes and stores to an elements backing store
-        // that the transition might change.
-        GVNFlagSet hoist_change_blockers = changes;
-        hoist_change_blockers.Add(kChangesMaps);
+            HValue::ConvertChangesToDependsFlags(instr->ChangesFlags());
+
+        // In addition, the transition must not be hoisted above elements kind
+        // changes, or if the transition is destructive to the elements buffer,
+        // changes to array pointer or array contents.
+        GVNFlagSet hoist_change_blockers;
+        hoist_change_blockers.Add(kChangesElementsKind);
         HTransitionElementsKind* trans = HTransitionElementsKind::cast(instr);
         if (trans->original_map()->has_fast_double_elements()) {
+          hoist_change_blockers.Add(kChangesElementsPointer);
           hoist_change_blockers.Add(kChangesDoubleArrayElements);
         }
         if (trans->transitioned_map()->has_fast_double_elements()) {
+          hoist_change_blockers.Add(kChangesElementsPointer);
           hoist_change_blockers.Add(kChangesArrayElements);
         }
         if (FLAG_trace_gvn) {
           GVNFlagSet hoist_blockers = hoist_depends_blockers;
           hoist_blockers.Add(hoist_change_blockers);
           GVNFlagSet first_time = *first_time_changes;
           first_time.Add(*first_time_depends);
           TRACE_GVN_4("Checking dependencies on HTransitionElementsKind "
                       "%d (%s) hoist blockers: %s; "
                       "first-time accumulated: %s\n",
@@ skipping 2135 matching lines @@
 
   set_current_block(loop_successor);
   Drop(5);
 
   set_current_block(loop_body);
 
   HValue* key = AddInstruction(
       new(zone()) HLoadKeyedFastElement(
           environment()->ExpressionStackAt(2),  // Enum cache.
           environment()->ExpressionStackAt(0),  // Iteration index.
-          HLoadKeyedFastElement::OMIT_HOLE_CHECK));
+          OMIT_HOLE_CHECK));
 
   // Check if the expected map still matches that of the enumerable.
   // If not just deoptimize.
   AddInstruction(new(zone()) HCheckMapValue(
       environment()->ExpressionStackAt(4),
       environment()->ExpressionStackAt(3)));
 
   Bind(each_var, key);
 
   BreakAndContinueInfo break_info(stmt, 5);
@@ skipping 270 matching lines @@
                           int* max_properties,
                           int* total_size) {
   ASSERT(max_depth >= 0 && *max_properties >= 0);
   if (max_depth == 0) return false;
 
   Handle<FixedArrayBase> elements(boilerplate->elements());
   if (elements->length() > 0 &&
       elements->map() != boilerplate->GetHeap()->fixed_cow_array_map()) {
     if (boilerplate->HasFastDoubleElements()) {
       *total_size += FixedDoubleArray::SizeFor(elements->length());
-    } else if (boilerplate->HasFastElements()) {
+    } else if (boilerplate->HasFastObjectElements()) {
       Handle<FixedArray> fast_elements = Handle<FixedArray>::cast(elements);
       int length = elements->length();
       for (int i = 0; i < length; i++) {
         if ((*max_properties)-- == 0) return false;
         Handle<Object> value(fast_elements->get(i));
         if (value->IsJSObject()) {
           Handle<JSObject> value_object = Handle<JSObject>::cast(value);
           if (!IsFastLiteral(value_object,
                              max_depth - 1,
                              max_properties,
@@ skipping 186 matching lines @@
     if (!Smi::IsValid(i)) return Bailout("Non-smi key in array literal");
 
     elements = new(zone()) HLoadElements(literal);
     AddInstruction(elements);
 
     HValue* key = AddInstruction(
         new(zone()) HConstant(Handle<Object>(Smi::FromInt(i)),
                               Representation::Integer32()));
 
     switch (boilerplate_elements_kind) {
-      case FAST_SMI_ONLY_ELEMENTS:
+      case FAST_SMI_ELEMENTS:
+      case FAST_HOLEY_SMI_ELEMENTS:
         // Smi-only arrays need a smi check.
         AddInstruction(new(zone()) HCheckSmi(value));
         // Fall through.
       case FAST_ELEMENTS:
+      case FAST_HOLEY_ELEMENTS:
         AddInstruction(new(zone()) HStoreKeyedFastElement(
             elements,
             key,
             value,
             boilerplate_elements_kind));
         break;
       case FAST_DOUBLE_ELEMENTS:
+      case FAST_HOLEY_DOUBLE_ELEMENTS:
         AddInstruction(new(zone()) HStoreKeyedFastDoubleElement(elements,
                                                                 key,
                                                                 value));
         break;
       default:
         UNREACHABLE();
         break;
     }
 
     AddSimulate(expr->GetIdForElement(i));
@@ skipping 737 matching lines @@
               val,
               Representation::Integer32(),
               true,  // Truncate to int32.
               false));  // Don't deoptimize undefined (irrelevant here).
         }
         break;
       }
       case EXTERNAL_FLOAT_ELEMENTS:
       case EXTERNAL_DOUBLE_ELEMENTS:
         break;
-      case FAST_SMI_ONLY_ELEMENTS:
+      case FAST_SMI_ELEMENTS:
       case FAST_ELEMENTS:
       case FAST_DOUBLE_ELEMENTS:
+      case FAST_HOLEY_SMI_ELEMENTS:
+      case FAST_HOLEY_ELEMENTS:
+      case FAST_HOLEY_DOUBLE_ELEMENTS:
       case DICTIONARY_ELEMENTS:
       case NON_STRICT_ARGUMENTS_ELEMENTS:
         UNREACHABLE();
         break;
     }
     return new(zone()) HStoreKeyedSpecializedArrayElement(
         external_elements, checked_key, val, elements_kind);
   } else {
     ASSERT(val == NULL);
     return new(zone()) HLoadKeyedSpecializedArrayElement(
         external_elements, checked_key, elements_kind);
   }
 }
 
 
 HInstruction* HGraphBuilder::BuildFastElementAccess(HValue* elements,
                                                     HValue* checked_key,
                                                     HValue* val,
                                                     ElementsKind elements_kind,
                                                     bool is_store) {
   if (is_store) {
     ASSERT(val != NULL);
     switch (elements_kind) {
       case FAST_DOUBLE_ELEMENTS:
+      case FAST_HOLEY_DOUBLE_ELEMENTS:
         return new(zone()) HStoreKeyedFastDoubleElement(
             elements, checked_key, val);
-      case FAST_SMI_ONLY_ELEMENTS:
+      case FAST_SMI_ELEMENTS:
+      case FAST_HOLEY_SMI_ELEMENTS:
         // Smi-only arrays need a smi check.
         AddInstruction(new(zone()) HCheckSmi(val));
         // Fall through.
       case FAST_ELEMENTS:
+      case FAST_HOLEY_ELEMENTS:
         return new(zone()) HStoreKeyedFastElement(
             elements, checked_key, val, elements_kind);
       default:
         UNREACHABLE();
         return NULL;
     }
   }
   // It's an element load (!is_store).
-  if (elements_kind == FAST_DOUBLE_ELEMENTS) {
-    return new(zone()) HLoadKeyedFastDoubleElement(elements, checked_key);
-  } else {  // FAST_ELEMENTS or FAST_SMI_ONLY_ELEMENTS.
-    return new(zone()) HLoadKeyedFastElement(elements, checked_key);
+  HoleCheckMode mode = IsFastPackedElementsKind(elements_kind) ?
+      OMIT_HOLE_CHECK :
+      PERFORM_HOLE_CHECK;
+  if (IsFastDoubleElementsKind(elements_kind)) {
+    return new(zone()) HLoadKeyedFastDoubleElement(elements, checked_key, mode);
+  } else {  // Smi or Object elements.
+    return new(zone()) HLoadKeyedFastElement(elements, checked_key, mode);
   }
 }
 
 
 HInstruction* HGraphBuilder::BuildMonomorphicElementAccess(HValue* object,
                                                            HValue* key,
                                                            HValue* val,
+                                                           HValue* dependency,
                                                            Handle<Map> map,
                                                            bool is_store) {
-  HInstruction* mapcheck = AddInstruction(new(zone()) HCheckMaps(object, map));
-  bool fast_smi_only_elements = map->has_fast_smi_only_elements();
-  bool fast_elements = map->has_fast_elements();
+  HInstruction* mapcheck = AddInstruction(new(zone())

[Jakob Kummerow, 2012/05/13 21:55:27]

nit: I'd break the line after "AddInstruction("

[danno, 2012/05/22 11:05:21]

Done.

+                                          HCheckMaps(object, map, dependency));
+  // No GVNFlag is necessary for ElementsKind if there is an explicit dependency
+  // on a HElementsTransition instruction. The flag can also be removed if the
+  // map to check has FAST_HOLEY_ELEMENTS, since there can be no further
+  // ElementsKind transitions. Finally, the dependency can be removed for stores
+  // for FAST_ELEMENTS, since a transition to HOLEY elements won't change the
+  // generated store code.
+  if (dependency ||
+      (map->elements_kind() == FAST_HOLEY_ELEMENTS) ||
+      (map->elements_kind() == FAST_ELEMENTS && is_store)) {
+    mapcheck->ClearGVNFlag(kDependsOnElementsKind);
+  }
+  bool fast_smi_only_elements = map->has_fast_smi_elements();
+  bool fast_elements = map->has_fast_object_elements();
   HInstruction* elements = AddInstruction(new(zone()) HLoadElements(object));
   if (is_store && (fast_elements || fast_smi_only_elements)) {
-    AddInstruction(new(zone()) HCheckMaps(
-        elements, isolate()->factory()->fixed_array_map()));
+    HCheckMaps* check_cow_map = new(zone()) HCheckMaps(
+        elements, isolate()->factory()->fixed_array_map());
+    check_cow_map->ClearGVNFlag(kDependsOnElementsKind);
+    AddInstruction(check_cow_map);
   }
   HInstruction* length = NULL;
   HInstruction* checked_key = NULL;
   if (map->has_external_array_elements()) {
     length = AddInstruction(new(zone()) HFixedArrayBaseLength(elements));
     checked_key = AddInstruction(new(zone()) HBoundsCheck(key, length));
     HLoadExternalArrayPointer* external_elements =
         new(zone()) HLoadExternalArrayPointer(elements);
     AddInstruction(external_elements);
     return BuildExternalArrayElementAccess(external_elements, checked_key,
@@ skipping 32 matching lines @@
     type_todo[i] = false;
   }
 
   // Elements_kind transition support.
   MapHandleList transition_target(maps->length());
   // Collect possible transition targets.
   MapHandleList possible_transitioned_maps(maps->length());
   for (int i = 0; i < maps->length(); ++i) {
     Handle<Map> map = maps->at(i);
     ElementsKind elements_kind = map->elements_kind();
-    if (elements_kind == FAST_DOUBLE_ELEMENTS ||
-        elements_kind == FAST_ELEMENTS) {
+    if (IsFastElementsKind(elements_kind) &&
+        elements_kind != GetInitialFastElementsKind()) {
       possible_transitioned_maps.Add(map);
     }
   }
   // Get transition target for each map (NULL == no transition).
   for (int i = 0; i < maps->length(); ++i) {
     Handle<Map> map = maps->at(i);
     Handle<Map> transitioned_map =
         map->FindTransitionedMap(&possible_transitioned_maps);
     transition_target.Add(transitioned_map);
   }
 
   int num_untransitionable_maps = 0;
   Handle<Map> untransitionable_map;
+  HTransitionElementsKind* transition = NULL;
   for (int i = 0; i < maps->length(); ++i) {
     Handle<Map> map = maps->at(i);
     ASSERT(map->IsMap());
     if (!transition_target.at(i).is_null()) {
-      AddInstruction(new(zone()) HTransitionElementsKind(
-          object, map, transition_target.at(i)));
+      ASSERT(Map::IsValidElementsTransition(
+          map->elements_kind(),
+          transition_target.at(i)->elements_kind()));
+      transition = new(zone()) HTransitionElementsKind(
+          object, map, transition_target.at(i));
+      AddInstruction(transition);
     } else {
       type_todo[map->elements_kind()] = true;
       if (map->elements_kind() >= FIRST_EXTERNAL_ARRAY_ELEMENTS_KIND) {
         todo_external_array = true;
       }
       num_untransitionable_maps++;
       untransitionable_map = map;
     }
   }
 
   // If only one map is left after transitioning, handle this case
   // monomorphically.
   if (num_untransitionable_maps == 1) {
     HInstruction* instr = NULL;
     if (untransitionable_map->has_slow_elements_kind()) {
       instr = AddInstruction(is_store ? BuildStoreKeyedGeneric(object, key, val)
                                       : BuildLoadKeyedGeneric(object, key));
     } else {
       instr = AddInstruction(BuildMonomorphicElementAccess(
-          object, key, val, untransitionable_map, is_store));
+          object, key, val, transition, untransitionable_map, is_store));
     }
     *has_side_effects |= instr->HasObservableSideEffects();
     instr->set_position(position);
     return is_store ? NULL : instr;
   }
 
   AddInstruction(HCheckInstanceType::NewIsSpecObject(object));
   HBasicBlock* join = graph()->CreateBasicBlock();
 
   HInstruction* elements_kind_instr =
       AddInstruction(new(zone()) HElementsKind(object));
   HCompareConstantEqAndBranch* elements_kind_branch = NULL;
   HInstruction* elements = AddInstruction(new(zone()) HLoadElements(object));
   HLoadExternalArrayPointer* external_elements = NULL;
   HInstruction* checked_key = NULL;
 
-  // Generated code assumes that FAST_SMI_ONLY_ELEMENTS, FAST_ELEMENTS,
-  // FAST_DOUBLE_ELEMENTS and DICTIONARY_ELEMENTS are handled before external
-  // arrays.
-  STATIC_ASSERT(FAST_SMI_ONLY_ELEMENTS < FIRST_EXTERNAL_ARRAY_ELEMENTS_KIND);
-  STATIC_ASSERT(FAST_ELEMENTS < FIRST_EXTERNAL_ARRAY_ELEMENTS_KIND);
+  // Generated code assumes that FAST_* and DICTIONARY_ELEMENTS ElementsKinds
+  // are handled before external arrays.
+  STATIC_ASSERT(FAST_SMI_ELEMENTS < FIRST_EXTERNAL_ARRAY_ELEMENTS_KIND);
+  STATIC_ASSERT(FAST_HOLEY_ELEMENTS < FIRST_EXTERNAL_ARRAY_ELEMENTS_KIND);
   STATIC_ASSERT(FAST_DOUBLE_ELEMENTS < FIRST_EXTERNAL_ARRAY_ELEMENTS_KIND);
   STATIC_ASSERT(DICTIONARY_ELEMENTS < FIRST_EXTERNAL_ARRAY_ELEMENTS_KIND);
 
   for (ElementsKind elements_kind = FIRST_ELEMENTS_KIND;
        elements_kind <= LAST_ELEMENTS_KIND;
        elements_kind = ElementsKind(elements_kind + 1)) {
-    // After having handled FAST_ELEMENTS, FAST_SMI_ONLY_ELEMENTS,
-    // FAST_DOUBLE_ELEMENTS and DICTIONARY_ELEMENTS, we need to add some code
-    // that's executed for all external array cases.
+    // After having handled FAST_* and DICTIONARY_ELEMENTS, we need to add some
+    // code that's executed for all external array cases.
     STATIC_ASSERT(LAST_EXTERNAL_ARRAY_ELEMENTS_KIND ==
                   LAST_ELEMENTS_KIND);
     if (elements_kind == FIRST_EXTERNAL_ARRAY_ELEMENTS_KIND
         && todo_external_array) {
       HInstruction* length =
           AddInstruction(new(zone()) HFixedArrayBaseLength(elements));
       checked_key = AddInstruction(new(zone()) HBoundsCheck(key, length));
       external_elements = new(zone()) HLoadExternalArrayPointer(elements);
       AddInstruction(external_elements);
     }
     if (type_todo[elements_kind]) {
       HBasicBlock* if_true = graph()->CreateBasicBlock();
       HBasicBlock* if_false = graph()->CreateBasicBlock();
       elements_kind_branch = new(zone()) HCompareConstantEqAndBranch(
           elements_kind_instr, elements_kind, Token::EQ_STRICT);
       elements_kind_branch->SetSuccessorAt(0, if_true);
       elements_kind_branch->SetSuccessorAt(1, if_false);
       current_block()->Finish(elements_kind_branch);
 
       set_current_block(if_true);
       HInstruction* access;
-      if (elements_kind == FAST_SMI_ONLY_ELEMENTS ||
-          elements_kind == FAST_ELEMENTS ||
-          elements_kind == FAST_DOUBLE_ELEMENTS) {
-        if (is_store && elements_kind != FAST_DOUBLE_ELEMENTS) {
+      if (IsFastElementsKind(elements_kind)) {
+        if (is_store && !IsFastDoubleElementsKind(elements_kind)) {
           AddInstruction(new(zone()) HCheckMaps(
               elements, isolate()->factory()->fixed_array_map(),
               elements_kind_branch));
         }
         // TODO(jkummerow): The need for these two blocks could be avoided
         // in one of two ways:
         // (1) Introduce ElementsKinds for JSArrays that are distinct from
         //     those for fast objects.
         // (2) Put the common instructions into a third "join" block. This
         //     requires additional AST IDs that we can deopt to from inside
@@ skipping 66 matching lines @@
                                                 bool* has_side_effects) {
   ASSERT(!expr->IsPropertyName());
   HInstruction* instr = NULL;
   if (expr->IsMonomorphic()) {
     Handle<Map> map = expr->GetMonomorphicReceiverType();
     if (map->has_slow_elements_kind()) {
       instr = is_store ? BuildStoreKeyedGeneric(obj, key, val)
                        : BuildLoadKeyedGeneric(obj, key);
     } else {
       AddInstruction(new(zone()) HCheckNonSmi(obj));
-      instr = BuildMonomorphicElementAccess(obj, key, val, map, is_store);
+      instr = BuildMonomorphicElementAccess(obj, key, val, NULL, map, is_store);
     }
   } else if (expr->GetReceiverTypes() != NULL &&
              !expr->GetReceiverTypes()->is_empty()) {
     return HandlePolymorphicElementAccess(
         obj, key, val, expr, ast_id, position, is_store, has_side_effects);
   } else {
     if (is_store) {
       instr = BuildStoreKeyedGeneric(obj, key, val);
     } else {
       instr = BuildLoadKeyedGeneric(obj, key);
@@ skipping 3402 matching lines @@
     }
   }
 
 #ifdef DEBUG
   if (graph_ != NULL) graph_->Verify(false);  // No full verify.
   if (allocator_ != NULL) allocator_->Verify();
 #endif
 }
 
 } }  // namespace v8::internal