[compiler] Delete extra map check.

Use HeapConstant for string_iterator_map rather than loading it
manually. This avoids unnecessary map checks.

BUG= v8:3822,v8:5267

Review-Url: https://codereview.chromium.org/2479563003
Cr-Commit-Position: refs/heads/master@{#40741}

src/compiler/js-builtin-reducer.cc

@@ -96,11 +96,13 @@ class JSCallReduction {
 
 JSBuiltinReducer::JSBuiltinReducer(Editor* editor, JSGraph* jsgraph,
                                    Flags flags,
-                                   CompilationDependencies* dependencies)
+                                   CompilationDependencies* dependencies,
+                                   Handle<Context> native_context)
     : AdvancedReducer(editor),
       dependencies_(dependencies),
       flags_(flags),
       jsgraph_(jsgraph),
+      native_context_(native_context),
       type_cache_(TypeCache::Get()) {}
 
 namespace {
@@ -1033,14 +1035,9 @@ Reduction JSBuiltinReducer::ReduceStringIterator(Node* node) {
   if (Node* receiver = GetStringWitness(node)) {
     Node* effect = NodeProperties::GetEffectInput(node);
     Node* control = NodeProperties::GetControlInput(node);
-    Node* context = NodeProperties::GetContextInput(node);
-
-    Node* native_context = effect = graph()->NewNode(
-        javascript()->LoadContext(0, Context::NATIVE_CONTEXT_INDEX, true),
-        context, context, effect);
-    Node* map = effect = graph()->NewNode(
-        javascript()->LoadContext(0, Context::STRING_ITERATOR_MAP_INDEX, true),
-        native_context, native_context, effect);
+
+    Node* map = jsgraph()->HeapConstant(
+        handle(native_context()->string_iterator_map(), isolate()));
 
     // allocate new iterator
     effect = graph()->NewNode(

src/compiler/js-builtin-reducer.h

@@ -38,7 +38,8 @@ class V8_EXPORT_PRIVATE JSBuiltinReducer final
   typedef base::Flags<Flag> Flags;
 
   JSBuiltinReducer(Editor* editor, JSGraph* jsgraph, Flags flags,
-                   CompilationDependencies* dependencies);
+                   CompilationDependencies* dependencies,
+                   Handle<Context> native_context);
   ~JSBuiltinReducer() final {}
 
   Reduction Reduce(Node* node) final;
@@ -104,6 +105,7 @@ class V8_EXPORT_PRIVATE JSBuiltinReducer final
   Factory* factory() const;
   JSGraph* jsgraph() const { return jsgraph_; }
   Isolate* isolate() const;
+  Handle<Context> native_context() const { return native_context_; }
   CommonOperatorBuilder* common() const;
   SimplifiedOperatorBuilder* simplified() const;
   JSOperatorBuilder* javascript() const;
@@ -112,6 +114,7 @@ class V8_EXPORT_PRIVATE JSBuiltinReducer final
   CompilationDependencies* const dependencies_;
   Flags const flags_;
   JSGraph* const jsgraph_;
+  Handle<Context> const native_context_;
   TypeCache const& type_cache_;
 };
 

src/compiler/pipeline.cc

@@ -918,7 +918,7 @@ struct TypedLoweringPhase {
         data->info()->is_deoptimization_enabled()
             ? JSBuiltinReducer::kDeoptimizationEnabled
             : JSBuiltinReducer::kNoFlags,
-        data->info()->dependencies());
+        data->info()->dependencies(), data->native_context());
     Handle<LiteralsArray> literals_array(data->info()->closure()->literals());
     JSCreateLowering create_lowering(
         &graph_reducer, data->info()->dependencies(), data->jsgraph(),

test/unittests/compiler/js-builtin-reducer-unittest.cc

@@ -33,8 +33,10 @@ class JSBuiltinReducerTest : public TypedGraphTest {
                     &machine);
     // TODO(titzer): mock the GraphReducer here for better unit testing.
     GraphReducer graph_reducer(zone(), graph());
+
     JSBuiltinReducer reducer(&graph_reducer, &jsgraph,
-                             JSBuiltinReducer::kNoFlags, nullptr);
+                             JSBuiltinReducer::kNoFlags, nullptr,
+                             native_context());
     return reducer.Reduce(node);
   }