[turbofan] Single entry into deferred regions

src/compiler/instruction.h

Index: src/compiler/instruction.h
diff --git a/src/compiler/instruction.h b/src/compiler/instruction.h
index 70338858a583df27ac546c83e1f1636ab16ba062..098c53c847ba9def1b43276b769009dea05e5e84 100644
--- a/src/compiler/instruction.h
+++ b/src/compiler/instruction.h
@@ -1380,9 +1380,10 @@ class InstructionSequence final : public ZoneObject {
   void PrintBlock(const RegisterConfiguration* config, int block_id) const;
   void PrintBlock(int block_id) const;
 
-  void ValidateEdgeSplitForm();
-  void ValidateDeferredBlockExitPaths();
-  void ValidateSSA();
+  void ValidateEdgeSplitForm() const;
+  void ValidateDeferredBlockExitPaths() const;
+  void ValidateDeferredBlockEntryPaths() const;
+  void ValidateSSA() const;
 
  private:
   friend std::ostream& operator<<(std::ostream& os,