Lithium: avoid registers for constants when possible.

src/x64/lithium-x64.h

Index: src/x64/lithium-x64.h
diff --git a/src/x64/lithium-x64.h b/src/x64/lithium-x64.h
index 9154b04cf5aa54c5f345dcdf1c1ae01153bceba1..9f5f2852832fcb70bc58590218bd06466e6242a3 100644
--- a/src/x64/lithium-x64.h
+++ b/src/x64/lithium-x64.h
@@ -2674,6 +2674,9 @@ class LChunkBuilder BASE_EMBEDDED {
   MUST_USE_RESULT LOperand* UseRegisterOrConstant(HValue* value);
   MUST_USE_RESULT LOperand* UseRegisterOrConstantAtStart(HValue* value);
 
+  // An input operand in a constant operand.
+  MUST_USE_RESULT LOperand* UseConstant(HValue* value);
+
   // An input operand in register, stack slot or a constant operand.
   // Will not be moved to a register even if one is freely available.
   MUST_USE_RESULT LOperand* UseAny(HValue* value);