Bias commutative single-use register inputs and support lea adds

src/hydrogen-instructions.h

Index: src/hydrogen-instructions.h
diff --git a/src/hydrogen-instructions.h b/src/hydrogen-instructions.h
index decc62705b28808de6ca0f78b66fc503421dbc5e..43204050d9e75c5e2a9d4d0d9cce3be56a68ae76 100644
--- a/src/hydrogen-instructions.h
+++ b/src/hydrogen-instructions.h
@@ -3357,16 +3357,27 @@ class HBinaryOperation: public HTemplateInstruction<3> {
   HValue* left() { return OperandAt(1); }
   HValue* right() { return OperandAt(2); }
 
-  // TODO(kasperl): Move these helpers to the IA-32 Lithium
-  // instruction sequence builder.
-  HValue* LeastConstantOperand() {
-    if (IsCommutative() && left()->IsConstant()) return right();
-    return left();
+  // True if switching left and right operands likely generates better code.
+  bool AreOperandsBetterSwitched() {
+    if (IsCommutative()) {

[Sven Panne, 2013/05/07 11:38:40]

Starting with "if (!IsCommutative()) return false;" is more readable IMHO, it
follows a "comb-like" pattern. Perhaps one could fold this into a single boolean
expression, but I am not sure if this is more readable or not.

[danno, 2013/05/08 08:37:18]

Done.

+      // 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;
+      // 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.
+      if (right()->UseCount() == 1) return true;
+    }
+    return false;
+  }
+
+  HValue* BetterLeftOperand() {
+    return AreOperandsBetterSwitched() ? right() : left();
   }
 
-  HValue* MostConstantOperand() {
-    if (IsCommutative() && left()->IsConstant()) return left();
-    return right();
+  HValue* BetterRightOperand() {
+    return AreOperandsBetterSwitched() ? left() : right();
   }
 
   void set_observed_input_representation(int index, Representation rep) {