[compiler] Remove broken support for undetectable strings.

src/mips64/lithium-codegen-mips64.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/v8.h"
 
 #include "src/code-factory.h"
 #include "src/code-stubs.h"
 #include "src/cpu-profiler.h"
 #include "src/hydrogen-osr.h"
@@ skipping 5840 matching lines @@
     __ JumpIfSmi(input, true_label);
     __ ld(input, FieldMemOperand(input, HeapObject::kMapOffset));
     __ LoadRoot(at, Heap::kHeapNumberMapRootIndex);
     *cmp1 = input;
     *cmp2 = Operand(at);
     final_branch_condition = eq;
 
   } else if (String::Equals(type_name, factory->string_string())) {
     __ JumpIfSmi(input, false_label);
     __ GetObjectType(input, input, scratch);
-    __ Branch(USE_DELAY_SLOT, false_label,
-              ge, scratch, Operand(FIRST_NONSTRING_TYPE));
-    // input is an object so we can load the BitFieldOffset even if we take the
-    // other branch.
-    __ lbu(at, FieldMemOperand(input, Map::kBitFieldOffset));
-    __ And(at, at, 1 << Map::kIsUndetectable);
-    *cmp1 = at;
-    *cmp2 = Operand(zero_reg);
-    final_branch_condition = eq;
+    *cmp1 = scratch;
+    *cmp2 = Operand(FIRST_NONSTRING_TYPE);
+    final_branch_condition = lt;
 
   } else if (String::Equals(type_name, factory->symbol_string())) {
     __ JumpIfSmi(input, false_label);
     __ GetObjectType(input, input, scratch);
     *cmp1 = scratch;
     *cmp2 = Operand(SYMBOL_TYPE);
     final_branch_condition = eq;
 
   } else if (String::Equals(type_name, factory->boolean_string())) {
     __ LoadRoot(at, Heap::kTrueValueRootIndex);
@@ skipping 368 matching lines @@
   __ Push(at, ToRegister(instr->function()));
   CallRuntime(Runtime::kPushBlockContext, 2, instr);
   RecordSafepoint(Safepoint::kNoLazyDeopt);
 }
 
 
 #undef __
 
 }  // namespace internal
 }  // namespace v8