[v8-dev] Optimise Math.floor(x/y) to use integer division for specific divisor....

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 122 matching lines @@
   V(LoadFunctionPrototype)                     \
   V(LoadGlobalCell)                            \
   V(LoadGlobalGeneric)                         \
   V(LoadKeyedFastDoubleElement)                \
   V(LoadKeyedFastElement)                      \
   V(LoadKeyedGeneric)                          \
   V(LoadKeyedSpecializedArrayElement)          \
   V(LoadNamedField)                            \
   V(LoadNamedFieldPolymorphic)                 \
   V(LoadNamedGeneric)                          \
+  V(MathFloorOfDiv)                            \
   V(Mod)                                       \
   V(Mul)                                       \
   V(ObjectLiteral)                             \
   V(OsrEntry)                                  \
   V(OuterContext)                              \
   V(Parameter)                                 \
   V(Power)                                     \
   V(PushArgument)                              \
   V(Random)                                    \
   V(RegExpLiteral)                             \
@@ skipping 1768 matching lines @@
           return Representation::Double();
         case kMathAbs:
           return representation();
         default:
           UNREACHABLE();
           return Representation::None();
       }
     }
   }
 
-  virtual HValue* Canonicalize() {
-    // If the input is integer32 then we replace the floor instruction
-    // with its inputs.  This happens before the representation changes are
-    // introduced.
-    if (op() == kMathFloor) {
-      if (value()->representation().IsInteger32()) return value();
-    }
-    return this;
-  }
+  virtual HValue* Canonicalize();
 
   BuiltinFunctionId op() const { return op_; }
   const char* OpName() const;
 
   DECLARE_CONCRETE_INSTRUCTION(UnaryMathOperation)
 
  protected:
   virtual bool DataEquals(HValue* other) {
     HUnaryMathOperation* b = HUnaryMathOperation::cast(other);
     return op_ == b->op();
@@ skipping 697 matching lines @@
       SetFlag(kUseGVN);
     }
   }
 
   virtual HType CalculateInferredType();
 
   DECLARE_ABSTRACT_INSTRUCTION(BitwiseBinaryOperation)
 };
 
 
+class HMathFloorOfDiv: public HBinaryOperation {
+ public:
+  HMathFloorOfDiv(HValue* context, HValue* left, HValue* right)
+      : HBinaryOperation(context, left, right) {
+    set_representation(Representation::Integer32());

[fschneider, 2012/03/28 09:59:18]

I think you can make GVN handle this instruction by setting the flag

SetFlag(kUseGVN)

and implementing the DataEquals-function like for other arithmetic operations.
In this case DataEquals would just return true.

[Alexandre, 2012/03/28 16:27:38]

Done.

+  }
+
+  virtual Representation RequiredInputRepresentation(int index) {
+    return Representation::Integer32();
+  }
+
+  DECLARE_CONCRETE_INSTRUCTION(MathFloorOfDiv)
+};
+
+
 class HArithmeticBinaryOperation: public HBinaryOperation {
  public:
   HArithmeticBinaryOperation(HValue* context, HValue* left, HValue* right)
       : HBinaryOperation(context, left, right) {
     set_representation(Representation::Tagged());
     SetFlag(kFlexibleRepresentation);
     SetAllSideEffects();
   }
 
   virtual void RepresentationChanged(Representation to) {
@@ skipping 2110 matching lines @@
   DECLARE_CONCRETE_INSTRUCTION(LoadFieldByIndex);
 };
 
 
 #undef DECLARE_INSTRUCTION
 #undef DECLARE_CONCRETE_INSTRUCTION
 
 } }  // namespace v8::internal
 
 #endif  // V8_HYDROGEN_INSTRUCTIONS_H_