[turbofan] Properly specialize JSCreateIterResultObject map.

src/compiler/js-create-lowering.cc

 // Copyright 2016 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/compiler/js-create-lowering.h"
 
 #include "src/allocation-site-scopes.h"
 #include "src/code-factory.h"
 #include "src/compilation-dependencies.h"
 #include "src/compiler/access-builder.h"
@@ skipping 704 matching lines @@
   a.Store(AccessBuilder::ForJSFunctionNextFunctionLink(), undefined);
   RelaxControls(node);
   a.FinishAndChange(node);
   return Changed(node);
 }
 
 Reduction JSCreateLowering::ReduceJSCreateIterResultObject(Node* node) {
   DCHECK_EQ(IrOpcode::kJSCreateIterResultObject, node->opcode());
   Node* value = NodeProperties::GetValueInput(node, 0);
   Node* done = NodeProperties::GetValueInput(node, 1);
-  Node* context = NodeProperties::GetContextInput(node);
   Node* effect = NodeProperties::GetEffectInput(node);
 
-  // Load the JSIteratorResult map for the {context}.
-  Node* native_context = effect = graph()->NewNode(
-      javascript()->LoadContext(0, Context::NATIVE_CONTEXT_INDEX, true),
-      context, context, effect);
-  Node* iterator_result_map = effect = graph()->NewNode(
-      javascript()->LoadContext(0, Context::ITERATOR_RESULT_MAP_INDEX, true),
-      native_context, native_context, effect);
+  Node* iterator_result_map;
+  Handle<Context> native_context;
+  if (GetSpecializationNativeContext(node).ToHandle(&native_context)) {
+    // Specialize to the constant JSIteratorResult map to enable map check
+    // elimination to eliminate subsequent checks in case of inlining.
+    iterator_result_map = jsgraph()->HeapConstant(
+        handle(native_context->iterator_result_map(), isolate()));
+  } else {
+    // Load the JSIteratorResult map for the {context}.
+    Node* context = NodeProperties::GetContextInput(node);
+    Node* native_context = effect = graph()->NewNode(
+        javascript()->LoadContext(0, Context::NATIVE_CONTEXT_INDEX, true),
+        context, context, effect);
+    iterator_result_map = effect = graph()->NewNode(
+        javascript()->LoadContext(0, Context::ITERATOR_RESULT_MAP_INDEX, true),
+        native_context, native_context, effect);
+  }
 
   // Emit code to allocate the JSIteratorResult instance.
   AllocationBuilder a(jsgraph(), effect, graph()->start());
   a.Allocate(JSIteratorResult::kSize);
   a.Store(AccessBuilder::ForMap(), iterator_result_map);
   a.Store(AccessBuilder::ForJSObjectProperties(),
           jsgraph()->EmptyFixedArrayConstant());
   a.Store(AccessBuilder::ForJSObjectElements(),
           jsgraph()->EmptyFixedArrayConstant());
   a.Store(AccessBuilder::ForJSIteratorResultValue(), value);
@@ skipping 519 matching lines @@
         return literals_array_;
       }
       break;
     }
     default:
       break;
   }
   return MaybeHandle<LiteralsArray>();
 }
 
+MaybeHandle<Context> JSCreateLowering::GetSpecializationNativeContext(
+    Node* node) {
+  Node* const context = NodeProperties::GetContextInput(node);
+  return NodeProperties::GetSpecializationNativeContext(context,
+                                                        native_context_);
+}
+
 Factory* JSCreateLowering::factory() const { return isolate()->factory(); }
 
 Graph* JSCreateLowering::graph() const { return jsgraph()->graph(); }
 
 Isolate* JSCreateLowering::isolate() const { return jsgraph()->isolate(); }
 
 JSOperatorBuilder* JSCreateLowering::javascript() const {
   return jsgraph()->javascript();
 }
 
 CommonOperatorBuilder* JSCreateLowering::common() const {
   return jsgraph()->common();
 }
 
 SimplifiedOperatorBuilder* JSCreateLowering::simplified() const {
   return jsgraph()->simplified();
 }
 
 MachineOperatorBuilder* JSCreateLowering::machine() const {
   return jsgraph()->machine();
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8