Use immediates when possible for HBoundsCheck and HLoadKeyedFastElement

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 12bdfb28aed4bb1966270cf28ef05c5433e91bf4..d473b6553557a32f5d5966754586493e56ac95d5 100644
--- a/src/x64/lithium-x64.h
+++ b/src/x64/lithium-x64.h
@@ -2135,7 +2135,11 @@ class LChunkBuilder BASE_EMBEDDED {
   template<int I, int T>
       LInstruction* DefineFixedDouble(LTemplateInstruction<1, I, T>* instr,
                                       XMMRegister reg);
+  // Must be called for any instruction that can deoptimize (unless
+  // |MarkAsCall| is called with CAN_DEOPTIMIZE_EAGERLY, which implies this).
   LInstruction* AssignEnvironment(LInstruction* instr);
+  // Must be called for any instruction that can trigger a GC (unless
+  // |MarkAsCall| is called, which implies this).
   LInstruction* AssignPointerMap(LInstruction* instr);
 
   enum CanDeoptimize { CAN_DEOPTIMIZE_EAGERLY, CANNOT_DEOPTIMIZE_EAGERLY };