[turbofan] optimize moves into merges

src/compiler/instruction.h

Index: src/compiler/instruction.h
diff --git a/src/compiler/instruction.h b/src/compiler/instruction.h
index fe411d612977cb115114c49ac6730738acb9fa14..47fbec8e85682cab7c46cf1e67bd923360c58fc9 100644
--- a/src/compiler/instruction.h
+++ b/src/compiler/instruction.h
@@ -82,6 +82,11 @@ class InstructionOperand {
     ConvertTo(kind, index, kInvalidVirtualRegister);
   }
 
+  // Useful for map/set keys.
+  bool operator<(const InstructionOperand& op) const {
+    return value_ < op.value_;
+  }
+
  protected:
   template <typename SubKindOperand>
   static SubKindOperand* New(Zone* zone, const SubKindOperand& op) {