[compiler] Remove broken support for undetectable strings.

src/full-codegen/mips64/full-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"
 
 #if V8_TARGET_ARCH_MIPS64
 
 // Note on Mips implementation:
 //
@@ skipping 5041 matching lines @@
   PrepareForBailoutBeforeSplit(expr, true, if_true, if_false);
 
   Factory* factory = isolate()->factory();
   if (String::Equals(check, factory->number_string())) {
     __ JumpIfSmi(v0, if_true);
     __ ld(v0, FieldMemOperand(v0, HeapObject::kMapOffset));
     __ LoadRoot(at, Heap::kHeapNumberMapRootIndex);
     Split(eq, v0, Operand(at), if_true, if_false, fall_through);
   } else if (String::Equals(check, factory->string_string())) {
     __ JumpIfSmi(v0, if_false);
-    // Check for undetectable objects => false.
     __ GetObjectType(v0, v0, a1);
-    __ Branch(if_false, ge, a1, Operand(FIRST_NONSTRING_TYPE));
-    __ lbu(a1, FieldMemOperand(v0, Map::kBitFieldOffset));
-    __ And(a1, a1, Operand(1 << Map::kIsUndetectable));
-    Split(eq, a1, Operand(zero_reg),
-          if_true, if_false, fall_through);
+    Split(lt, a1, Operand(FIRST_NONSTRING_TYPE), if_true, if_false,
+          fall_through);
   } else if (String::Equals(check, factory->symbol_string())) {
     __ JumpIfSmi(v0, if_false);
     __ GetObjectType(v0, v0, a1);
     Split(eq, a1, Operand(SYMBOL_TYPE), if_true, if_false, fall_through);
   } else if (String::Equals(check, factory->boolean_string())) {
     __ LoadRoot(at, Heap::kTrueValueRootIndex);
     __ Branch(if_true, eq, v0, Operand(at));
     __ LoadRoot(at, Heap::kFalseValueRootIndex);
     Split(eq, v0, Operand(at), if_true, if_false, fall_through);
   } else if (String::Equals(check, factory->undefined_string())) {
@@ skipping 333 matching lines @@
          reinterpret_cast<uint64_t>(
              isolate->builtins()->OsrAfterStackCheck()->entry()));
   return OSR_AFTER_STACK_CHECK;
 }
 
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_TARGET_ARCH_MIPS64