Eliminate redundant smi checks

src/hydrogen-instructions.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 601 matching lines @@
   void ChangeRepresentation(Representation r) {
     // Representation was already set and is allowed to be changed.
     ASSERT(!r.IsNone());
     ASSERT(CheckFlag(kFlexibleRepresentation));
     RepresentationChanged(r);
     representation_ = r;
   }
   void AssumeRepresentation(Representation r);
 
   virtual bool IsConvertibleToInteger() const { return true; }
+  virtual bool IsValueTaggedSmi() const { return false; }

[Michael Starzinger, 2012/06/12 08:10:43]

Can't we use HValue::CalculateInferredType instead of this new method?

[danno, 2012/06/12 09:59:22]

No, unfortunately not. The representation is tagged, not integer. What this
method indicates additionally that it is always a SMI, and that can't be
expressed with the representation. 

On 2012/06/12 08:10:43, Michael Starzinger wrote:

[Michael Starzinger, 2012/06/12 10:48:05]

Yes, I agree, the representation has to be tagged. But on top of the
representation we can calculate the inferred type of the value (that is
represented as a tagged value). And I think that HType::Smi() actually indicates
a tagged Smi value. We use the same for HStringLength as well, it has a tagged
representation, but a Smi inferred type.

On 2012/06/12 09:59:22, danno wrote:

 
   HType type() const { return type_; }
   void set_type(HType new_type) {
     ASSERT(new_type.IsSubtypeOf(type_));
     type_ = new_type;
   }
 
   // An operation needs to override this function iff:
   //   1) it can produce an int32 output.
   //   2) the true value of its output can potentially be minus zero.
@@ skipping 1209 matching lines @@
   DECLARE_CONCRETE_INSTRUCTION(CallRuntime)
 
  private:
   const Runtime::Function* c_function_;
   Handle<String> name_;
 };
 
 
 class HJSArrayLength: public HTemplateInstruction<2> {
  public:
-  HJSArrayLength(HValue* value, HValue* typecheck) {
+  HJSArrayLength(HValue* value, HValue* typecheck,
+                 bool result_is_smi)

[Michael Starzinger, 2012/06/12 08:10:43]

Can we use an enum instead of a bool flag here?

[danno, 2012/06/12 09:59:22]

Done.

+      : result_is_smi_(result_is_smi) {
     // The length of an array is stored as a tagged value in the array
     // object. It is guaranteed to be 32 bit integer, but it can be
     // represented as either a smi or heap number.
     SetOperandAt(0, value);
     SetOperandAt(1, typecheck);
     set_representation(Representation::Tagged());
     SetFlag(kUseGVN);
     SetGVNFlag(kDependsOnArrayLengths);
     SetGVNFlag(kDependsOnMaps);
   }
 
   virtual Representation RequiredInputRepresentation(int index) {
     return Representation::Tagged();
   }
 
   virtual void PrintDataTo(StringStream* stream);
 
   HValue* value() { return OperandAt(0); }
   HValue* typecheck() { return OperandAt(1); }
 
+  virtual bool IsValueTaggedSmi() const {

[Michael Starzinger, 2012/06/12 08:10:43]

See first comment in this file.

[danno, 2012/06/12 09:59:22]

See my reply above. 
On 2012/06/12 08:10:43, Michael Starzinger wrote:

+    return result_is_smi_;
+  }
+
   DECLARE_CONCRETE_INSTRUCTION(JSArrayLength)
 
  protected:
-  virtual bool DataEquals(HValue* other) { return true; }
+  virtual bool DataEquals(HValue* other_raw) {
+    HJSArrayLength* other = HJSArrayLength::cast(other_raw);
+        return result_is_smi_ == other->result_is_smi_;
+  }
+
+ private:
+  bool result_is_smi_;
 };
 
 
 class HFixedArrayBaseLength: public HUnaryOperation {
  public:
   explicit HFixedArrayBaseLength(HValue* value) : HUnaryOperation(value) {
     set_representation(Representation::Tagged());
     SetFlag(kUseGVN);
     SetGVNFlag(kDependsOnArrayLengths);
   }
@@ skipping 2087 matching lines @@
 class ArrayInstructionInterface {
  public:
   virtual HValue* GetKey() = 0;
   virtual void SetKey(HValue* key) = 0;
   virtual void SetIndexOffset(uint32_t index_offset) = 0;
   virtual bool IsDehoisted() = 0;
   virtual void SetDehoisted(bool is_dehoisted) = 0;
   virtual ~ArrayInstructionInterface() { };
 };
 
-
 enum HoleCheckMode { PERFORM_HOLE_CHECK, OMIT_HOLE_CHECK };
 
 class HLoadKeyedFastElement
     : public HTemplateInstruction<2>, public ArrayInstructionInterface {
  public:
   HLoadKeyedFastElement(HValue* obj,
                         HValue* key,
-                        HoleCheckMode hole_check_mode = PERFORM_HOLE_CHECK)
-      : hole_check_mode_(hole_check_mode),
-        index_offset_(0),
-        is_dehoisted_(false) {
+                        HoleCheckMode mode,
+                        ElementsKind elements_kind = FAST_ELEMENTS)
+      : bit_field_(0) {
+    ASSERT(IsFastSmiOrObjectElementsKind(elements_kind));
+    ASSERT(mode == OMIT_HOLE_CHECK ||
+           IsFastHoleyElementsKind(elements_kind));
+    bit_field_ = ElementsKindField::encode(elements_kind) |
+        HoleCheckModeField::encode(mode);
     SetOperandAt(0, obj);
     SetOperandAt(1, key);
     set_representation(Representation::Tagged());
     SetGVNFlag(kDependsOnArrayElements);
     SetFlag(kUseGVN);
   }
 
   HValue* object() { return OperandAt(0); }
   HValue* key() { return OperandAt(1); }
-  uint32_t index_offset() { return index_offset_; }
-  void SetIndexOffset(uint32_t index_offset) { index_offset_ = index_offset; }
+  uint32_t index_offset() { return IndexOffsetField::decode(bit_field_); }
+  void SetIndexOffset(uint32_t index_offset) {
+    bit_field_ = IndexOffsetField::update(bit_field_, index_offset);
+  }
   HValue* GetKey() { return key(); }
   void SetKey(HValue* key) { SetOperandAt(1, key); }
-  bool IsDehoisted() { return is_dehoisted_; }
-  void SetDehoisted(bool is_dehoisted) { is_dehoisted_ = is_dehoisted; }
+  bool IsDehoisted() { return IsDehoistedField::decode(bit_field_); }
+  void SetDehoisted(bool is_dehoisted) {
+    bit_field_ = IsDehoistedField::update(bit_field_, is_dehoisted);
+  }
+  ElementsKind elements_kind() const {
+    return ElementsKindField::decode(bit_field_);
+  }
+  HoleCheckMode hole_check_mode() const {
+    return HoleCheckModeField::decode(bit_field_);
+  }
+
+  virtual bool IsValueTaggedSmi() const {
+    return IsFastSmiElementsKind(elements_kind()) &&
+        IsFastPackedElementsKind(elements_kind());
+  }
 
   virtual Representation RequiredInputRepresentation(int index) {
     // The key is supposed to be Integer32.
     return index == 0
       ? Representation::Tagged()
       : Representation::Integer32();
   }
 
   virtual void PrintDataTo(StringStream* stream);
 
   bool RequiresHoleCheck();
 
   DECLARE_CONCRETE_INSTRUCTION(LoadKeyedFastElement)
 
  protected:
   virtual bool DataEquals(HValue* other) {
     if (!other->IsLoadKeyedFastElement()) return false;
     HLoadKeyedFastElement* other_load = HLoadKeyedFastElement::cast(other);
-    if (is_dehoisted_ && index_offset_ != other_load->index_offset_)
+    if (IsDehoisted() && index_offset() != other_load->index_offset())
       return false;
-    return hole_check_mode_ == other_load->hole_check_mode_;
+    return elements_kind() == other_load->elements_kind() &&
+        hole_check_mode() == other_load->hole_check_mode();
   }
 
  private:
-  HoleCheckMode hole_check_mode_;
-  uint32_t index_offset_;
-  bool is_dehoisted_;
+  class ElementsKindField:  public BitField<ElementsKind, 0, 4> {};
+  class IndexOffsetField:   public BitField<uint32_t, 4, 25> {};
+  class HoleCheckModeField: public BitField<HoleCheckMode, 29, 1> {};
+  class IsDehoistedField:   public BitField<bool, 30, 1> {};
+  uint32_t bit_field_;
 };
 
 
 class HLoadKeyedFastDoubleElement
     : public HTemplateInstruction<2>, public ArrayInstructionInterface {
  public:
   HLoadKeyedFastDoubleElement(
     HValue* elements,
     HValue* key,
     HoleCheckMode hole_check_mode = PERFORM_HOLE_CHECK)
-    : index_offset_(0),
-      is_dehoisted_(false),
-      hole_check_mode_(hole_check_mode) {
-        SetOperandAt(0, elements);
-        SetOperandAt(1, key);
-        set_representation(Representation::Double());
+      : index_offset_(0),
+        is_dehoisted_(false),
+        hole_check_mode_(hole_check_mode) {
+    SetOperandAt(0, elements);
+    SetOperandAt(1, key);
+    set_representation(Representation::Double());
     SetGVNFlag(kDependsOnDoubleArrayElements);
     SetFlag(kUseGVN);
-      }
+  }
 
   HValue* elements() { return OperandAt(0); }
   HValue* key() { return OperandAt(1); }
   uint32_t index_offset() { return index_offset_; }
   void SetIndexOffset(uint32_t index_offset) { index_offset_ = index_offset; }
   HValue* GetKey() { return key(); }
   void SetKey(HValue* key) { SetOperandAt(1, key); }
   bool IsDehoisted() { return is_dehoisted_; }
   void SetDehoisted(bool is_dehoisted) { is_dehoisted_ = is_dehoisted; }
 
@@ skipping 1022 matching lines @@
   DECLARE_CONCRETE_INSTRUCTION(LoadFieldByIndex);
 };
 
 
 #undef DECLARE_INSTRUCTION
 #undef DECLARE_CONCRETE_INSTRUCTION
 
 } }  // namespace v8::internal
 
 #endif  // V8_HYDROGEN_INSTRUCTIONS_H_