[string] Optimize ToDirectStringAssembler for sequential strings

src/code-stub-assembler.cc

Index: src/code-stub-assembler.cc
diff --git a/src/code-stub-assembler.cc b/src/code-stub-assembler.cc
index 63f2462884f421350e33818b4c260c2867c3e5c2..a12587751cc4b8ded25ef17d5e226a92c1dc0ad3 100644
--- a/src/code-stub-assembler.cc
+++ b/src/code-stub-assembler.cc
@@ -3363,7 +3363,8 @@ Node* ToDirectStringAssembler::TryToDirect(Label* if_bailout) {
   Label if_isthin(this);
   Label out(this);
 
-  Goto(&dispatch);
+  Branch(IsSequentialStringInstanceType(var_instance_type_.value()), &out,
+         &dispatch);
 
   // Dispatch based on string representation.
   Bind(&dispatch);
@@ -3440,7 +3441,7 @@ Node* ToDirectStringAssembler::TryToSequential(StringPointerKind ptr_kind,
   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);