[compiler] Remove broken support for undetectable strings.

src/arm64/lithium-codegen-arm64.cc

 // Copyright 2013 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/arm64/frames-arm64.h"
 #include "src/arm64/lithium-codegen-arm64.h"
 #include "src/arm64/lithium-gap-resolver-arm64.h"
 #include "src/base/bits.h"
@@ skipping 5921 matching lines @@
         __ B(chunk_->GetAssemblyLabel(false_block));
       }
     }
 
   } else if (String::Equals(type_name, factory->string_string())) {
     DCHECK((instr->temp1() != NULL) && (instr->temp2() != NULL));
     Register map = ToRegister(instr->temp1());
     Register scratch = ToRegister(instr->temp2());
 
     __ JumpIfSmi(value, false_label);
-    __ JumpIfObjectType(
-        value, map, scratch, FIRST_NONSTRING_TYPE, false_label, ge);
-    __ Ldrb(scratch, FieldMemOperand(map, Map::kBitFieldOffset));
-    EmitTestAndBranch(instr, eq, scratch, 1 << Map::kIsUndetectable);
+    __ CompareObjectType(value, map, scratch, FIRST_NONSTRING_TYPE);
+    EmitBranch(instr, lt);
 
   } else if (String::Equals(type_name, factory->symbol_string())) {
     DCHECK((instr->temp1() != NULL) && (instr->temp2() != NULL));
     Register map = ToRegister(instr->temp1());
     Register scratch = ToRegister(instr->temp2());
 
     __ JumpIfSmi(value, false_label);
     __ CompareObjectType(value, map, scratch, SYMBOL_TYPE);
     EmitBranch(instr, eq);
 
@@ skipping 206 matching lines @@
   Handle<ScopeInfo> scope_info = instr->scope_info();
   __ Push(scope_info);
   __ Push(ToRegister(instr->function()));
   CallRuntime(Runtime::kPushBlockContext, 2, instr);
   RecordSafepoint(Safepoint::kNoLazyDeopt);
 }
 
 
 }  // namespace internal
 }  // namespace v8