Use immediates when possible for HBoundsCheck and HLoadKeyedFastElement

src/x64/lithium-x64.cc

Index: src/x64/lithium-x64.cc
diff --git a/src/x64/lithium-x64.cc b/src/x64/lithium-x64.cc
index 7f4490f6defa9e573d34420af985827f30403748..c73f681efb3ffad6b3c88168f51312e788dc407a 100644
--- a/src/x64/lithium-x64.cc
+++ b/src/x64/lithium-x64.cc
@@ -1529,8 +1529,9 @@ LInstruction* LChunkBuilder::DoValueOf(HValueOf* instr) {
 
 
 LInstruction* LChunkBuilder::DoBoundsCheck(HBoundsCheck* instr) {
-  return AssignEnvironment(new LBoundsCheck(UseRegisterAtStart(instr->index()),
-                                            Use(instr->length())));
+  return AssignEnvironment(new LBoundsCheck(
+      UseRegisterOrConstantAtStart(instr->index()),
+      Use(instr->length())));
 }
 
 
@@ -1829,9 +1830,9 @@ LInstruction* LChunkBuilder::DoLoadKeyedFastElement(
   ASSERT(instr->representation().IsTagged());
   ASSERT(instr->key()->representation().IsInteger32());
   LOperand* obj = UseRegisterAtStart(instr->object());
-  LOperand* key = UseRegisterAtStart(instr->key());
+  LOperand* key = UseRegisterOrConstantAtStart(instr->key());
   LLoadKeyedFastElement* result = new LLoadKeyedFastElement(obj, key);
-  return AssignEnvironment(DefineSameAsFirst(result));
+  return AssignEnvironment(DefineAsRegister(result));
 }