Eliminate map checks of constant values.

src/hydrogen-instructions.h

Index: src/hydrogen-instructions.h
diff --git a/src/hydrogen-instructions.h b/src/hydrogen-instructions.h
index 763b6369e3583a0a1c9b1a41bd3af7e93e8fe34e..a6935cc44c625799aa66e9dbca14c66f2d250da6 100644
--- a/src/hydrogen-instructions.h
+++ b/src/hydrogen-instructions.h
@@ -2732,12 +2732,7 @@ class HLoadExternalArrayPointer: public HUnaryOperation {
 class HCheckMaps: public HTemplateInstruction<2> {
  public:
   static HCheckMaps* New(HValue* value, Handle<Map> map, Zone* zone,
-                         HValue *typecheck = NULL) {
-    HCheckMaps* check_map = new(zone) HCheckMaps(value, zone, typecheck);
-    check_map->map_set_.Add(map, zone);
-    return check_map;
-  }
-
+                         CompilationInfo* info, HValue *typecheck = NULL);
   static HCheckMaps* New(HValue* value, SmallMapList* maps, Zone* zone,
                          HValue *typecheck = NULL) {
     HCheckMaps* check_map = new(zone) HCheckMaps(value, zone, typecheck);
@@ -2771,6 +2766,8 @@ class HCheckMaps: public HTemplateInstruction<2> {
     return check_map;
   }
 
+  bool CanOmitMapChecks() { return omit_; }
+
   virtual bool HasEscapingOperandAt(int index) { return false; }
   virtual Representation RequiredInputRepresentation(int index) {
     return Representation::Tagged();
@@ -2806,7 +2803,7 @@ class HCheckMaps: public HTemplateInstruction<2> {
  private:
   // Clients should use one of the static New* methods above.
   HCheckMaps(HValue* value, Zone *zone, HValue* typecheck)
-      : map_unique_ids_(0, zone) {
+      : omit_(false), map_unique_ids_(0, zone) {
     SetOperandAt(0, value);
     // Use the object value for the dependency if NULL is passed.
     // TODO(titzer): do GVN flags already express this dependency?
@@ -2818,6 +2815,16 @@ class HCheckMaps: public HTemplateInstruction<2> {
     SetGVNFlag(kDependsOnElementsKind);
   }
 
+  void omit(CompilationInfo* info) {
+    omit_ = true;
+    for (int i = 0; i < map_set_.length(); i++) {
+      Handle<Map> map = map_set_.at(i);
+      map->AddDependentCompilationInfo(DependentCode::kPrototypeCheckGroup,
+                                       info);
+    }
+  }
+
+  bool omit_;
   SmallMapList map_set_;
   ZoneList<UniqueValueId> map_unique_ids_;
 };
@@ -3296,6 +3303,11 @@ class HConstant: public HTemplateInstruction<0> {
     return handle_;
   }
 
+  bool InstanceOf(Handle<Map> map) {
+    return handle_->IsJSObject() &&
+        Handle<JSObject>::cast(handle_)->map() == *map;
+  }
+
   bool IsSpecialDouble() const {
     return has_double_value_ &&
         (BitCast<int64_t>(double_value_) == BitCast<int64_t>(-0.0) ||