Improve constant element index access code generation

src/x64/lithium-codegen-x64.cc

Index: src/x64/lithium-codegen-x64.cc
diff --git a/src/x64/lithium-codegen-x64.cc b/src/x64/lithium-codegen-x64.cc
index 3e688dfd004c7bc4aa29dfa2637ce62ba6203bc4..0d8bf77cd1b4da9aafd093d6d039057bb25ebe26 100644
--- a/src/x64/lithium-codegen-x64.cc
+++ b/src/x64/lithium-codegen-x64.cc
@@ -3617,8 +3617,13 @@ void LCodeGen::DoBoundsCheck(LBoundsCheck* instr) {
       __ AbortIfNotZeroExtended(reg);
     }
     if (instr->index()->IsConstantOperand()) {
-      __ cmpq(reg,
-              Immediate(ToInteger32(LConstantOperand::cast(instr->index()))));
+      int constant_index =
+          ToInteger32(LConstantOperand::cast(instr->index()));
+      if (instr->hydrogen()->length()->representation().IsTagged()) {
+        __ Cmp(reg, Smi::FromInt(constant_index));
+      } else {
+        __ cmpq(reg, Immediate(constant_index));
+      }
     } else {
       Register reg2 = ToRegister(instr->index());
       if (FLAG_debug_code &&