Fix LBoundsCheck on x64 to handle (stack slot + constant) correctly

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 8e887cd915f0e68b5a9d110796caa96b6e752629..cab8d377b0a1291076ffafa12aa49d38aa7e227c 100644
--- a/src/x64/lithium-codegen-x64.cc
+++ b/src/x64/lithium-codegen-x64.cc
@@ -3774,11 +3774,17 @@ void LCodeGen::DoBoundsCheck(LBoundsCheck* instr) {
       __ cmpq(reg, reg2);
     }
   } else {
+    Operand length = ToOperand(instr->length());
     if (instr->index()->IsConstantOperand()) {
-      __ cmpq(ToOperand(instr->length()),
-              Immediate(ToInteger32(LConstantOperand::cast(instr->index()))));
+      int constant_index =
+          ToInteger32(LConstantOperand::cast(instr->index()));
+      if (instr->hydrogen()->length()->representation().IsTagged()) {
+        __ Cmp(length, Smi::FromInt(constant_index));
+      } else {
+        __ cmpq(length, Immediate(constant_index));
+      }
     } else {
-      __ cmpq(ToOperand(instr->length()), ToRegister(instr->index()));
+      __ cmpq(length, ToRegister(instr->index()));
     }
   }
   DeoptimizeIf(below_equal, instr->environment());