Indirectly dispatch all backtracking jumps through the same block.

runtime/vm/regexp_assembler.h

Index: runtime/vm/regexp_assembler.h
diff --git a/runtime/vm/regexp_assembler.h b/runtime/vm/regexp_assembler.h
index 92a7f28dd382f62a953e3edbf1d85458514f2692..58bcfd4fb3f0f6ac6e53a51d63ddbe61e12b0599 100644
--- a/runtime/vm/regexp_assembler.h
+++ b/runtime/vm/regexp_assembler.h
@@ -328,25 +328,20 @@ class IRRegExpMacroAssembler: public RegExpMacroAssembler {
 
   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.
@@ -567,9 +562,13 @@ class IRRegExpMacroAssembler: public RegExpMacroAssembler {
   GraphEntryInstr* entry_block_;
   JoinEntryInstr* start_block_;
   JoinEntryInstr* success_block_;
-  JoinEntryInstr* backtrack_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_;
+  IndirectGotoInstr* backtrack_goto_;
+
   const ParsedFunction* parsed_function_;
   const ZoneGrowableArray<const ICData*>& ic_data_array_;
 
@@ -617,8 +616,6 @@ class IRRegExpMacroAssembler: public RegExpMacroAssembler {
   // The actual array object used as the stack.
   GrowableObjectArray& stack_array_;
 
-  GrowableArray<IndirectGotoInstr*> igotos_;
-
   IdAllocator block_id_;
   IdAllocator temp_id_;
   IdAllocator arg_id_;