[regexp] break recursion in mutually recursive capture/back references.

src/parsing/parser.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/parsing/parser.h"
 
 #include "src/api.h"
 #include "src/ast/ast.h"
 #include "src/ast/ast-expression-visitor.h"
 #include "src/ast/ast-literal-reindexer.h"
@@ skipping 5547 matching lines @@
         CharacterRange::AddClassEscape(c, ranges, zone());
         RegExpTree* atom = new(zone()) RegExpCharacterClass(ranges, false);
         builder->AddAtom(atom);
         break;
       }
       case '1': case '2': case '3': case '4': case '5': case '6':
       case '7': case '8': case '9': {
         int index = 0;
         if (ParseBackReferenceIndex(&index)) {
           if (state->IsInsideCaptureGroup(index)) {
-            // The backreference is inside the capture group it refers to.
-            // Nothing can possibly have been captured yet.
+            // The back reference is inside the capture group it refers to.
+            // Nothing can possibly have been captured yet, so we use empty
+            // instead. This ensures that, when checking a back reference,
+            // the capture registers of the referenced capture are either
+            // both set or both cleared.
             builder->AddEmpty();
           } else {
             RegExpCapture* capture = GetCapture(index);
             RegExpTree* atom = new (zone()) RegExpBackReference(capture);
             builder->AddAtom(atom);
           }
           break;
         }
         uc32 first_digit = Next();
         if (first_digit == '8' || first_digit == '9') {
@@ skipping 1008 matching lines @@
 
 void ParserTraits::QueueDestructuringAssignmentForRewriting(Expression* expr) {
   DCHECK(expr->IsRewritableAssignmentExpression());
   parser_->function_state_->AddDestructuringAssignment(
       Parser::DestructuringAssignment(expr, parser_->scope_));
 }
 
 
 }  // namespace internal
 }  // namespace v8