Improve polymorphic loads on single slots.

src/hydrogen-instructions.h

Index: src/hydrogen-instructions.h
diff --git a/src/hydrogen-instructions.h b/src/hydrogen-instructions.h
index a05fc776f848875e561e14e7c982229602b0134a..9203b3081657ffa7b60edbc8247bd64967fa573e 100644
--- a/src/hydrogen-instructions.h
+++ b/src/hydrogen-instructions.h
@@ -86,6 +86,7 @@ class LChunkBuilder;
   V(CheckFunction)                             \
   V(CheckInstanceType)                         \
   V(CheckMap)                                  \
+  V(CheckMapSet)                               \
   V(CheckNonSmi)                               \
   V(CheckPrototypeMaps)                        \
   V(CheckSmi)                                  \
@@ -2050,6 +2051,43 @@ class HCheckMap: public HTemplateInstruction<2> {
 };
 
 
+class HCheckMapSet: public HTemplateInstruction<1> {

[danno, 2012/03/09 11:52:58]

Please merge with HCheckMap as discussed

[Michael Starzinger, 2012/03/12 11:37:11]

Done. HCheckMap now works with a SmallMapList backing structure and has two
constructors, one taking a single map and the other a set of maps. Also added a
static helper to construct HCheckMaps which allow transitions.

+ public:
+  HCheckMapSet(HValue* value, SmallMapList* map_set) : map_set_(map_set) {
+    map_set->Sort();
+    SetOperandAt(0, value);
+    set_representation(Representation::Tagged());
+    SetFlag(kUseGVN);
+    SetGVNFlag(kDependsOnMaps);
+    SetGVNFlag(kDependsOnElementsKind);
+  }
+
+  virtual Representation RequiredInputRepresentation(int index) {
+    return Representation::Tagged();
+  }
+  virtual void PrintDataTo(StringStream* stream);
+
+  HValue* value() { return OperandAt(0); }
+  SmallMapList* map_set() const { return map_set_; }
+
+  DECLARE_CONCRETE_INSTRUCTION(CheckMapSet)
+
+ protected:
+  virtual bool DataEquals(HValue* other) {

[danno, 2012/03/09 11:52:58]

Fast case single maps by just comparing b->map_set() == map_set()

[Michael Starzinger, 2012/03/12 11:37:11]

The backing SmallMapList cannot be compared by reference. But it already has all
the necessary fast-case code for singletons implemented. So I think relying on
the below loop being executed just once should be efficient enough.

+    HCheckMapSet* b = HCheckMapSet::cast(other);
+    // Relies on the fact that map_set has been sorted before.
+    if (map_set_->length() != b->map_set()->length()) return false;
+    for (int i = 0; i < map_set_->length(); i++) {
+      if (!map_set_->at(i).is_identical_to(b->map_set()->at(i))) return false;
+    }
+    return true;
+  }
+
+ private:
+  SmallMapList* map_set_;
+};
+
+
 class HCheckFunction: public HUnaryOperation {
  public:
   HCheckFunction(HValue* value, Handle<JSFunction> function)