Tweak the Better{Left,Right}Operand() heuristic

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 949 matching lines @@
     UNREACHABLE();
     return false;
   }
 
   virtual Representation RepresentationFromInputs() {
     return representation();
   }
   Representation RepresentationFromUses();
   Representation RepresentationFromUseRequirements();
   bool HasNonSmiUse();
+  bool UsedBy(HValue* value);
   virtual void UpdateRepresentation(Representation new_rep,
                                     HInferRepresentationPhase* h_infer,
                                     const char* reason);
   void AddDependantsToWorklist(HInferRepresentationPhase* h_infer);
 
   virtual void RepresentationChanged(Representation to) { }
 
   virtual Range* InferRange(Zone* zone);
   virtual void DeleteFromGraph() = 0;
   virtual void InternalSetOperandAt(int index, HValue* value) = 0;
@@ skipping 2558 matching lines @@
   HValue* context() const { return OperandAt(0); }
   HValue* left() const { return OperandAt(1); }
   HValue* right() const { return OperandAt(2); }
 
   // True if switching left and right operands likely generates better code.
   bool AreOperandsBetterSwitched() {
     if (!IsCommutative()) return false;
 
     // Constant operands are better off on the right, they can be inlined in
     // many situations on most platforms.
-    if (left()->IsConstant()) return true;
-    if (right()->IsConstant()) return false;
+    if (left()->IsConstant() &&
+        (!representation().IsDouble() || left()->UseCount() > 1)) {
+      return true;
+    }
+    if (right()->IsConstant() &&
+        (!representation().IsDouble() || right()->UseCount() > 1)) {
+      return false;
+    }
+
+    if (left()->IsPhi() && UsedBy(left())) return false;
+    if (right()->IsPhi() && UsedBy(right())) return true;
 

[haitao.feng, 2014/05/15 05:56:20]

How about writing codes in this way?
-    if (left()->IsConstant()) return true;
-    if (right()->IsConstant()) return false;
+    if (left()->IsConstant() && left()->EmitAtUses()) return true;
+    if (right()->IsConstant() && right()->EmitAtUses()) return false;
+
+    // If destination is one operand of the phi node, they might be allocated
+    // to the same register by hinting.
+    if (left()->IsPhi()) {
+      HPhi* phi = HPhi::cast(left());
+      for (int i = 0; i < phi->OperandCount(); i++) {
+        if (phi->OperandAt(i) == this) return false;
+      }
+    } else if (right()->IsPhi()) {
+      HPhi* phi = HPhi::cast(right());
+      for (int i = 0; i < phi->OperandCount(); i++) {
+        if (phi->OperandAt(i) == this) return true;
+      }
+    }

     // Otherwise, if there is only one use of the right operand, it would be
     // better off on the left for platforms that only have 2-arg arithmetic
     // ops (e.g ia32, x64) that clobber the left operand.
     return right()->UseCount() == 1;
   }
 
   HValue* BetterLeftOperand() {
     return AreOperandsBetterSwitched() ? right() : left();
   }
 
@@ skipping 3393 matching lines @@
   virtual bool IsDeletable() const V8_OVERRIDE { return true; }
 };
 
 
 #undef DECLARE_INSTRUCTION
 #undef DECLARE_CONCRETE_INSTRUCTION
 
 } }  // namespace v8::internal
 
 #endif  // V8_HYDROGEN_INSTRUCTIONS_H_