Indirectly dispatch all backtracking jumps through the same block.

runtime/vm/regexp_assembler.h

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #ifndef VM_REGEXP_ASSEMBLER_H_
 #define VM_REGEXP_ASSEMBLER_H_
 
 #include "vm/assembler.h"
 #include "vm/intermediate_language.h"
 #include "vm/object.h"
@@ skipping 310 matching lines @@
   virtual void ReadStackPointerFromRegister(intptr_t reg);
   virtual void SetCurrentPositionFromEnd(intptr_t by);
   virtual void SetRegister(intptr_t register_index, intptr_t to);
   virtual bool Succeed();
   virtual void WriteCurrentPositionToRegister(intptr_t reg, intptr_t cp_offset);
   virtual void ClearRegisters(intptr_t reg_from, intptr_t reg_to);
   virtual void WriteStackPointerToRegister(intptr_t reg);
 
   virtual void PrintBlocks();
 
+  IndirectGotoInstr* backtrack_goto() const { return backtrack_goto_; }
   GraphEntryInstr* graph_entry() const { return entry_block_; }
 
   intptr_t num_stack_locals() const { return local_id_.Count(); }
   intptr_t num_blocks() const { return block_id_.Count(); }
 
-  // A table mapping block ids to block offsets, used to look up offsets
-  // for indirect goto instructions.
-  void FinalizeBlockOffsetTable();
-
-  // Fill in indirect goto successors.
-  void FinalizeIndirectGotos();
+  // Generate a dispatch block implementing backtracking. Must be done after
+  // graph construction.
+  void GenerateBacktrackBlock();
 
  private:
   // Generate the contents of preset blocks. The entry block is the entry point
   // of the generated code.
   void GenerateEntryBlock();
-  // Performs backtracking, i.e. popping an offset from the stack and doing
-  // an indirect goto.
-  void GenerateBacktrackBlock();
   // Copies capture indices into the result area and returns true.
   void GenerateSuccessBlock();
   // Returns false.
   void GenerateExitBlock();
 
   enum ComparisonKind {
     kEQ,
     kNE,
     kLT,
     kGT,
@@ skipping 200 matching lines @@
   // Which mode to generate code for (ASCII or UC16).
   Mode mode_;
 
   // Which specific string class to generate code for.
   intptr_t specialization_cid_;
 
   // Block entries used internally.
   GraphEntryInstr* entry_block_;
   JoinEntryInstr* start_block_;
   JoinEntryInstr* success_block_;
+  JoinEntryInstr* exit_block_;
+
+  // TODO(zerny): Implement IR support for "computed gotos" and replace all uses

[Vyacheslav Egorov (Google), 2014/11/13 18:30:04]

igoto is a computed goto - so this comment seems a bit strange. 

implement a "different IR support" might work, but overall I think you can just
drop it :)

[zerny-google, 2014/11/14 13:29:29]

Yes. I'll drop it from here and add a TODO to the IR declaration about avoiding
the "embedded" gotos.

+  // of the backtracking block by direct jumps.
   JoinEntryInstr* backtrack_block_;
-  JoinEntryInstr* exit_block_;
+  IndirectGotoInstr* backtrack_goto_;
 
   const ParsedFunction* parsed_function_;
   const ZoneGrowableArray<const ICData*>& ic_data_array_;
 
   // All created blocks are contained within this set. Used for printing
   // the generated code.
   GrowableArray<BlockEntryInstr*> blocks_;
 
   // The current instruction to link to when new code is emitted.
   Instruction* current_instruction_;
@@ skipping 28 matching lines @@
 
   LocalVariable* result_;
 
   // Stored positions containing group bounds. Generated as needed.
   const intptr_t position_registers_count_;
   GrowableArray<LocalVariable*> position_registers_;
 
   // The actual array object used as the stack.
   GrowableObjectArray& stack_array_;
 
-  GrowableArray<IndirectGotoInstr*> igotos_;
-
   IdAllocator block_id_;
   IdAllocator temp_id_;
   IdAllocator arg_id_;
   IdAllocator local_id_;
   IdAllocator indirect_id_;
 };
 
 
 }  // namespace dart
 
 #endif  // VM_REGEXP_ASSEMBLER_H_