Indirectly dispatch all backtracking jumps through the same block.

runtime/vm/regexp_assembler.cc

Index: runtime/vm/regexp_assembler.cc
diff --git a/runtime/vm/regexp_assembler.cc b/runtime/vm/regexp_assembler.cc
index 60382d87162f5b5910e0a03e7001f705fa03a2dc..23e9c4178c354556fba7a354d40d86015169b116 100644
--- a/runtime/vm/regexp_assembler.cc
+++ b/runtime/vm/regexp_assembler.cc
@@ -125,7 +125,6 @@ IRRegExpMacroAssembler::IRRegExpMacroAssembler(
 
   GenerateEntryBlock();
   GenerateSuccessBlock();
-  GenerateBacktrackBlock();
   GenerateExitBlock();
 
   blocks_.Add(entry_block_);
@@ -208,7 +207,30 @@ void IRRegExpMacroAssembler::GenerateEntryBlock() {
 void IRRegExpMacroAssembler::GenerateBacktrackBlock() {
   set_current_instruction(backtrack_block_);
   TAG();
-  Backtrack();
+  CheckPreemption();
+
+  const intptr_t entries_count = entry_block_->indirect_entries().length();
+
+  GrowableObjectArray& offsets = GrowableObjectArray::ZoneHandle(
+      I, GrowableObjectArray::New(entries_count, Heap::kOld));
+
+  PushArgumentInstr* block_offsets_push =
+      PushArgument(Bind(new(I) ConstantInstr(offsets)));
+  PushArgumentInstr* block_id_push = PushArgument(PopStack());
+
+  Value* offset_value =
+      Bind(InstanceCall(InstanceCallDescriptor::FromToken(Token::kINDEX),
+                        block_offsets_push,
+                        block_id_push));
+
+  backtrack_goto_ = new(I) IndirectGotoInstr(&offsets, offset_value);
+  CloseBlockWith(backtrack_goto_);
+
+  // Add an edge from the "indirect" goto to each of the targets.
+  for (intptr_t j = 0; j < entries_count; j++) {
+    backtrack_goto_->AddSuccessor(
+        TargetWithJoinGoto(entry_block_->indirect_entries().At(j)));
+  }
 }
 
 
@@ -723,23 +745,7 @@ void IRRegExpMacroAssembler::AdvanceRegister(intptr_t reg, intptr_t by) {
 
 void IRRegExpMacroAssembler::Backtrack() {
   TAG();
-  CheckPreemption();
-
-  GrowableObjectArray& offsets = GrowableObjectArray::ZoneHandle(
-        I, GrowableObjectArray::New(Heap::kOld));
-
-  PushArgumentInstr* block_offsets_push =
-      PushArgument(Bind(new(I) ConstantInstr(offsets)));
-  PushArgumentInstr* block_id_push = PushArgument(PopStack());
-
-  Value* offset_value =
-      Bind(InstanceCall(InstanceCallDescriptor::FromToken(Token::kINDEX),
-                        block_offsets_push,
-                        block_id_push));
-
-  IndirectGotoInstr* igoto = new(I) IndirectGotoInstr(&offsets, offset_value);
-  CloseBlockWith(igoto);
-  igotos_.Add(igoto);
+  GoTo(backtrack_block_);
 }
 
 
@@ -779,53 +785,6 @@ LocalVariable* IRRegExpMacroAssembler::position_register(intptr_t index) {
 }
 
 
-// TODO(zerny): Move the offset table outside to avoid having to keep
-// the assembler around until after code generation; both function or regexp
-// would work.
-void IRRegExpMacroAssembler::FinalizeBlockOffsetTable() {
-  for (intptr_t i = 0; i < igotos_.length(); i++) {
-    IndirectGotoInstr* igoto = igotos_[i];
-    igoto->SetOffsetCount(I, indirect_id_.Count());
-
-    for (intptr_t j = 0; j < igoto->SuccessorCount(); j++) {
-      TargetEntryInstr* target = igoto->SuccessorAt(j);
-
-      // Optimizations might have modified the immediate target block, but
-      // it must end with a goto to the indirect entry.
-      Instruction* instr = target;
-      while (instr != NULL && !instr->IsGoto()) {
-        instr = instr->next();
-      }
-      ASSERT(instr->IsGoto());
-
-      IndirectEntryInstr* ientry =
-          instr->AsGoto()->successor()->AsIndirectEntry();
-      ASSERT(ientry != NULL);
-
-      // The intermediate block was possibly compacted, check both it and the
-      // final indirect entry for a valid offset. If neither are valid, then
-      // the indirect entry is unreachable.
-      intptr_t offset =
-          (target->offset() > 0) ? target->offset() : ientry->offset();
-      if (offset > 0) {
-        intptr_t adjusted_offset =
-            offset - Assembler::EntryPointToPcMarkerOffset();
-        igoto->SetOffsetAt(I, ientry->indirect_id(), adjusted_offset);
-      }
-    }
-  }
-}
-
-void IRRegExpMacroAssembler::FinalizeIndirectGotos() {
-  for (intptr_t i = 0; i < igotos_.length(); i++) {
-    for (intptr_t j = 0; j < entry_block_->indirect_entries().length(); j++) {
-      igotos_.At(i)->AddSuccessor(
-            TargetWithJoinGoto(entry_block_->indirect_entries().At(j)));
-    }
-  }
-}
-
-
 void IRRegExpMacroAssembler::CheckCharacter(uint32_t c, BlockLabel* on_equal) {
   TAG();
   Definition* cur_char_def = LoadLocal(current_character_);