Foundation for the use of informative definitions in Crankshaft.

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 655 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,
+  // smi checks...).
+  // We call these instructions "informative definitions", or "iDef".
+  // One of the iDef operands is special because it is the value that is
+  // "transferred" to the output, we call it the "redefined operand".
+  // If an HValue is an iDef it must override RedefinedOperandIndex() so that
+  // it does not return kNoRedefinedOperand;
+  static const int kNoRedefinedOperand = -1;
+  virtual int RedefinedOperandIndex() { return kNoRedefinedOperand; }
+  bool IsInformativelDefinition() {

[Jakob Kummerow, 2013/01/29 10:33:01]

nit: s/IsInformativelDefinition/IsInformativeDefinition/

[Massi, 2013/01/29 15:39:00]

Done.

+    return RedefinedOperandIndex() != kNoRedefinedOperand;
+  }
+  HValue* RedefinedOperand() {
+    ASSERT(IsInformativelDefinition());
+    return OperandAt(RedefinedOperandIndex());
+  }
+
+  // This method must always return the original HValue SSA definition
+  // (regardless of any iDef of this value).
+  HValue* ActualValue() {
+    return IsInformativelDefinition()
+        ? RedefinedOperand()->ActualValue() : this;

[Jakob Kummerow, 2013/01/29 10:33:01]

nit: preferred formatting: 
    return IsInformativeDefinition() ? RedefinedOperand()->ActualValue()
                                     : this;

[Massi, 2013/01/29 15:39:00]

Done.

+  }
+
   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 2327 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 int RedefinedOperandIndex() { return 0; }
+
   DECLARE_CONCRETE_INSTRUCTION(BoundsCheck)
 
  protected:
   virtual bool DataEquals(HValue* other) { return true; }
   BoundsCheckKeyMode key_mode_;
 };
 
 
 class HBitwiseBinaryOperation: public HBinaryOperation {
  public:
@@ skipping 1355 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() { };
+
+  static Representation KeyedAccessIndexRequirement(Representation r) {
+    return r.IsInteger32()
+        ? Representation::Integer32() : Representation::Tagged();

[Jakob Kummerow, 2013/01/29 10:33:01]

nit: preferred formatting:
    return r.IsInteger32() ? Representation::Integer32()
                           : Representation::Tagged();

[Massi, 2013/01/29 15:39:00]

Done.

+  }
 };
 
 
 class HLoadKeyed
     : public HTemplateInstruction<3>, public ArrayInstructionInterface {
  public:
   HLoadKeyed(HValue* obj,
              HValue* key,
              HValue* dependency,
              ElementsKind elements_kind)
@@ skipping 63 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 ArrayInstructionInterface::KeyedAccessIndexRequirement(
+          OperandAt(1)->representation());
+    }
     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 ArrayInstructionInterface::KeyedAccessIndexRequirement(
+          OperandAt(1)->representation());
     }
 
     ASSERT_EQ(index, 2);
     if (IsDoubleOrFloatElementsKind(elements_kind())) {
       return Representation::Double();
     }
 
     return is_external() ? Representation::Integer32()
                          : Representation::Tagged();
   }
@@ skipping 794 matching lines @@
   virtual bool IsDeletable() const { return true; }
 };
 
 
 #undef DECLARE_INSTRUCTION
 #undef DECLARE_CONCRETE_INSTRUCTION
 
 } }  // namespace v8::internal
 
 #endif  // V8_HYDROGEN_INSTRUCTIONS_H_