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

src/hydrogen-instructions.h

Index: src/hydrogen-instructions.h
===================================================================
--- src/hydrogen-instructions.h	(revision 10969)
+++ src/hydrogen-instructions.h	(working copy)
@@ -140,6 +140,7 @@
   V(LoadNamedField)                            \
   V(LoadNamedFieldPolymorphic)                 \
   V(LoadNamedGeneric)                          \
+  V(MathFloorOfDiv)                            \
   V(Mod)                                       \
   V(Mul)                                       \
   V(ObjectLiteral)                             \
@@ -1928,15 +1929,7 @@
     }
   }
 
-  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;
@@ -2654,6 +2647,21 @@
 };
 
 
+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)