Make the array bounds check elimination phase optional (and set the foundation for introducing SSI …

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 330 matching lines @@
   bool IsNone() const { return kind_ == kNone; }
   bool IsTagged() const { return kind_ == kTagged; }
   bool IsInteger32() const { return kind_ == kInteger32; }
   bool IsDouble() const { return kind_ == kDouble; }
   bool IsExternal() const { return kind_ == kExternal; }
   bool IsSpecialization() const {
     return kind_ == kInteger32 || kind_ == kDouble;
   }
   const char* Mnemonic() const;
 
+  Representation KeyedAccessIndexRequirement() {

[Jakob Kummerow, 2013/01/10 16:06:47]

nit: I'm a bit unhappy about adding instruction-specific logic to the
Representation class. Three alternative suggestions, pick what you like:
1) Inline it. It's only one line, after all.
2) Move to a static method of ArrayInstructionInterface.
3) Move to a file-global static function "Representation
ArrayIndexRepresentation(Representation r) {...}" as close as possible to the
two call sites.

+    return IsInteger32() ? Integer32() : Tagged();
+  }
+
  private:
   explicit Representation(Kind k) : kind_(k) { }
 
   // Make sure kind fits in int8.
   STATIC_ASSERT(kNumRepresentations <= (1 << kBitsPerByte));
 
   int8_t kind_;
 };
 
 
@@ skipping 304 matching lines @@
   // If the operation also exists in a form that takes int32 and outputs int32
   // then the operation should return its input value so that we can propagate
   // back.  There are three operations that need to propagate back to more than
   // one input.  They are phi and binary div and mul.  They always return NULL
   // and expect the caller to take care of things.
   virtual HValue* EnsureAndPropagateNotMinusZero(BitVector* visited) {
     visited->Add(id());
     return NULL;
   }
 
+  // There are HInstructions that do not really change a value, they
+  // only add pieces of information to it (like bounds checks, map checks
+  // or SSI definitions after conditional branches).
+  // This method must always return the original HValue SSA definition (the
+  // register allocator relies on this to avoid allocating multiple registers
+  // for the same value).
+  virtual HValue* ActualValue() { return this; }
+
   bool IsDefinedAfter(HBasicBlock* other) const;
 
   // Operands.
   virtual int OperandCount() = 0;
   virtual HValue* OperandAt(int index) const = 0;
   void SetOperandAt(int index, HValue* value);
 
   void DeleteAndReplaceWith(HValue* other);
   void ReplaceAllUsesWith(HValue* other);
   bool HasNoUses() const { return use_list_ == NULL; }
@@ skipping 2263 matching lines @@
 
 enum BoundsCheckKeyMode {
   DONT_ALLOW_SMI_KEY,
   ALLOW_SMI_KEY
 };
 
 
 class HBoundsCheck: public HTemplateInstruction<2> {
  public:
   HBoundsCheck(HValue* index, HValue* length,
-               BoundsCheckKeyMode key_mode = DONT_ALLOW_SMI_KEY)
+               BoundsCheckKeyMode key_mode = DONT_ALLOW_SMI_KEY,
+               Representation r = Representation::None())
       : key_mode_(key_mode) {
     SetOperandAt(0, index);
     SetOperandAt(1, length);
-    set_representation(Representation::Integer32());
+    if (r.IsNone()) {
+      // In the normal compilation pipeline the representation is flexible
+      // (see comment to RequiredInputRepresentation).
+      SetFlag(kFlexibleRepresentation);
+    } else {
+      // When compiling stubs we want to set the representation explicitly
+      // so the compilation pipeline can skip the HInferRepresentation phase.
+      set_representation(r);
+    }
     SetFlag(kUseGVN);
   }
 
   virtual Representation RequiredInputRepresentation(int arg_index) {
-    if (key_mode_ == DONT_ALLOW_SMI_KEY ||
-        !length()->representation().IsTagged()) {
-      return Representation::Integer32();
-    }
-    // If the index is tagged and isn't constant, then allow the length
-    // to be tagged, since it is usually already tagged from loading it out of
-    // the length field of a JSArray. This allows for direct comparison without
-    // untagging.
-    if (index()->representation().IsTagged() && !index()->IsConstant()) {
-      return Representation::Tagged();
-    }
-    // Also allow the length to be tagged if the index is constant, because
-    // it can be tagged to allow direct comparison.
-    if (index()->IsConstant() &&
-        index()->representation().IsInteger32() &&
-        arg_index == 1) {
-      return Representation::Tagged();
-    }
-    return Representation::Integer32();
+    return representation();
   }
   virtual Representation observed_input_representation(int index) {
     return Representation::Integer32();
   }
 
   virtual void PrintDataTo(StringStream* stream);
+  virtual void InferRepresentation(HInferRepresentation* h_infer);
 
   HValue* index() { return OperandAt(0); }
   HValue* length() { return OperandAt(1); }
 
+  virtual HValue* ActualValue() {
+    return index();
+  }
+
   DECLARE_CONCRETE_INSTRUCTION(BoundsCheck)
 
  protected:
   virtual bool DataEquals(HValue* other) { return true; }
   BoundsCheckKeyMode key_mode_;
 };
 
 
 class HBitwiseBinaryOperation: public HBinaryOperation {
  public:
@@ skipping 1433 matching lines @@
   }
 
   virtual Representation RequiredInputRepresentation(int index) {
     // kind_fast:       tagged[int32] (none)
     // kind_double:     tagged[int32] (none)
     // kind_external: external[int32] (none)
     if (index == 0) {
       return is_external() ? Representation::External()
           : Representation::Tagged();
     }
-    if (index == 1) return Representation::Integer32();
+    if (index == 1) {
+      return OperandAt(1)->representation().KeyedAccessIndexRequirement();
+    }
     return Representation::None();
   }
 
   virtual Representation observed_input_representation(int index) {
     return RequiredInputRepresentation(index);
   }
 
   virtual void PrintDataTo(StringStream* stream);
 
   bool RequiresHoleCheck() const;
@@ skipping 194 matching lines @@
   }
 
   virtual Representation RequiredInputRepresentation(int index) {
     // kind_fast:       tagged[int32] = tagged
     // kind_double:     tagged[int32] = double
     // kind_external: external[int32] = (double | int32)
     if (index == 0) {
       return is_external() ? Representation::External()
                            : Representation::Tagged();
     } else if (index == 1) {
-      return Representation::Integer32();
+      return OperandAt(1)->representation().KeyedAccessIndexRequirement();
     }
 
     ASSERT_EQ(index, 2);
     if (IsDoubleOrFloatElementsKind(elements_kind())) {
       return Representation::Double();
     }
 
     return is_external() ? Representation::Integer32()
                          : Representation::Tagged();
   }
@@ skipping 771 matching lines @@
   virtual bool IsDeletable() const { return true; }
 };
 
 
 #undef DECLARE_INSTRUCTION
 #undef DECLARE_CONCRETE_INSTRUCTION
 
 } }  // namespace v8::internal
 
 #endif  // V8_HYDROGEN_INSTRUCTIONS_H_