Use weak cell to embed map in CompareNil IC.

src/hydrogen.cc

 // Copyright 2013 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/hydrogen.h"
 
 #include <sstream>
 
 #include "src/v8.h"
 
@@ skipping 2998 matching lines @@
   // And the result of the length
   HValue* length = AddLoadArrayLength(boilerplate, kind);
   Add<HStoreNamedField>(result, HObjectAccess::ForArrayLength(kind), length);
 
   BuildCopyElements(boilerplate_elements, kind, elements,
                     kind, length, NULL);
   return result;
 }
 
 
-void HGraphBuilder::BuildCompareNil(
-    HValue* value,
-    Type* type,
-    HIfContinuation* continuation) {
+void HGraphBuilder::BuildCompareNil(HValue* value, Type* type,
+                                    HIfContinuation* continuation,
+                                    MapEmbedding map_embedding) {
   IfBuilder if_nil(this);
   bool some_case_handled = false;
   bool some_case_missing = false;
 
   if (type->Maybe(Type::Null())) {
     if (some_case_handled) if_nil.Or();
     if_nil.If<HCompareObjectEqAndBranch>(value, graph()->GetConstantNull());
     some_case_handled = true;
   } else {
     some_case_missing = true;
@@ skipping 18 matching lines @@
 
   if (some_case_missing) {
     if_nil.Then();
     if_nil.Else();
     if (type->NumClasses() == 1) {
       BuildCheckHeapObject(value);
       // For ICs, the map checked below is a sentinel map that gets replaced by
       // the monomorphic map when the code is used as a template to generate a
       // new IC. For optimized functions, there is no sentinel map, the map
       // emitted below is the actual monomorphic map.
-      Add<HCheckMaps>(value, type->Classes().Current());
+      if (map_embedding == kEmbedMapsViaWeakCells) {
+        HValue* cell =
+            Add<HConstant>(Map::WeakCellForMap(type->Classes().Current()));
+        HValue* expected_map = Add<HLoadNamedField>(
+            cell, nullptr, HObjectAccess::ForWeakCellValue());
+        HValue* map =
+            Add<HLoadNamedField>(value, nullptr, HObjectAccess::ForMap());
+        IfBuilder map_check(this);
+        map_check.IfNot<HCompareObjectEqAndBranch>(expected_map, map);
+        map_check.ThenDeopt("Unknown map");
+        map_check.End();
+      } else {
+        DCHECK(map_embedding == kEmbedMapsDirectly);
+        Add<HCheckMaps>(value, type->Classes().Current());
+      }
     } else {
       if_nil.Deopt("Too many undetectable types");
     }
   }
 
   if_nil.CaptureContinuation(continuation);
 }
 
 
 void HGraphBuilder::BuildCreateAllocationMemento(
@@ skipping 10363 matching lines @@
   if (ShouldProduceTraceOutput()) {
     isolate()->GetHTracer()->TraceHydrogen(name(), graph_);
   }
 
 #ifdef DEBUG
   graph_->Verify(false);  // No full verify.
 #endif
 }
 
 } }  // namespace v8::internal