Indirectly dispatch all backtracking jumps through the same block.

runtime/vm/intermediate_language.cc

 // Copyright (c) 2013, 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.
 
 #include "vm/intermediate_language.h"
 
 #include "vm/bit_vector.h"
 #include "vm/cpu.h"
 #include "vm/dart_entry.h"
 #include "vm/flow_graph_allocator.h"
@@ skipping 2512 matching lines @@
     compiler->AddCurrentDescriptor(RawPcDescriptors::kDeopt,
                                    GetDeoptId(),
                                    Scanner::kNoSourcePos);
   }
   if (HasParallelMove()) {
     compiler->parallel_move_resolver()->EmitNativeCode(parallel_move());
   }
 }
 
 
+void IndirectGotoInstr::ComputeOffsetTable(Isolate* isolate) {
+  ASSERT(SuccessorCount() == offsets_.Capacity());
+  offsets_.SetLength(SuccessorCount());
+  for (intptr_t i = 0; i < SuccessorCount(); i++) {
+    TargetEntryInstr* target = SuccessorAt(i);
+
+    // Optimizations might have modified the immediate target block, but
+    // it must end with a goto to the indirect entry.
+    Instruction* instr = target;

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

use target->last_instruction() instead of the loop?

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

No can do, since it is not set if the target is unreachable :-(

+    while (instr != NULL && !instr->IsGoto()) {
+      instr = instr->next();
+    }
+    ASSERT(instr->IsGoto());
+
+    IndirectEntryInstr* ientry =
+        instr->AsGoto()->successor()->AsIndirectEntry();
+    ASSERT(ientry != NULL);
+    ASSERT(ientry->indirect_id() == i);
+
+    // The intermediate block might be 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 =

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

when can the ientry be unreachable?

if it is "unreachable" then why is it connected to the IndirectGotoInstr in the
first place?

[zerny-google, 2014/11/14 13:29:28]

It is possible that we never emit a backtracking point despite the regexp
containing branches (also after this CL since here the backtrack block is
unconditionally created). I've added an early escape to this method to avoid
computing tables for an unreachable dispatch instruction.

+        (target->offset() > 0) ? target->offset() : ientry->offset();
+
+    if (offset > 0) {
+      offset -= Assembler::EntryPointToPcMarkerOffset();
+      offsets_.SetAt(i, Smi::ZoneHandle(isolate, Smi::New(offset)));
+    }
+  }
+}
+
+
 LocationSummary* IndirectEntryInstr::MakeLocationSummary(
     Isolate* isolate, bool optimizing) const {
   return JoinEntryInstr::MakeLocationSummary(isolate, optimizing);
 }
 
 
 void IndirectEntryInstr::EmitNativeCode(FlowGraphCompiler* compiler) {
   JoinEntryInstr::EmitNativeCode(compiler);
 }
 
@@ skipping 835 matching lines @@
     case Token::kTRUNCDIV: return 0;
     case Token::kMOD: return 1;
     default: UNIMPLEMENTED(); return -1;
   }
 }
 
 
 #undef __
 
 }  // namespace dart