[string] Optimize ToDirectStringAssembler for sequential strings

src/code-stub-assembler.cc

 // Copyright 2016 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/code-stub-assembler.h"
 #include "src/code-factory.h"
 #include "src/frames-inl.h"
 #include "src/frames.h"
 
 namespace v8 {
 namespace internal {
@@ skipping 3345 matching lines @@
 
 Node* ToDirectStringAssembler::TryToDirect(Label* if_bailout) {
   VariableList vars({&var_string_, &var_offset_, &var_instance_type_}, zone());
   Label dispatch(this, vars);
   Label if_iscons(this);
   Label if_isexternal(this);
   Label if_issliced(this);
   Label if_isthin(this);
   Label out(this);
 
-  Goto(&dispatch);
+  Branch(IsSequentialStringInstanceType(var_instance_type_.value()), &out,
+         &dispatch);
 
   // Dispatch based on string representation.
   Bind(&dispatch);
   {
     int32_t values[] = {
         kSeqStringTag,    kConsStringTag, kExternalStringTag,
         kSlicedStringTag, kThinStringTag,
     };
     Label* labels[] = {
         &out, &if_iscons, &if_isexternal, &if_issliced, &if_isthin,
@@ skipping 56 matching lines @@
 
   Bind(&out);
   return var_string_.value();
 }
 
 Node* ToDirectStringAssembler::TryToSequential(StringPointerKind ptr_kind,
                                                Label* if_bailout) {
   CHECK(ptr_kind == PTR_TO_DATA || ptr_kind == PTR_TO_STRING);
 
   Variable var_result(this, MachineType::PointerRepresentation());
-  Label out(this), if_issequential(this), if_isexternal(this);
+  Label out(this), if_issequential(this), if_isexternal(this, Label::kDeferred);
   Branch(is_external(), &if_isexternal, &if_issequential);
 
   Bind(&if_issequential);
   {
     STATIC_ASSERT(SeqOneByteString::kHeaderSize ==
                   SeqTwoByteString::kHeaderSize);
     Node* result = BitcastTaggedToWord(var_string_.value());
     if (ptr_kind == PTR_TO_DATA) {
       result = IntPtrAdd(result, IntPtrConstant(SeqOneByteString::kHeaderSize -
                                                 kHeapObjectTag));
@@ skipping 4818 matching lines @@
         formatted.c_str(), TENURED);
     CallRuntime(Runtime::kGlobalPrint, NoContextConstant(),
                 HeapConstant(string));
   }
   CallRuntime(Runtime::kDebugPrint, NoContextConstant(), tagged_value);
 #endif
 }
 
 }  // namespace internal
 }  // namespace v8