[regexp] Fold repeated assertions

src/regexp/regexp-parser.cc

 // Copyright 2016 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/regexp/regexp-parser.h"
 
 #include "src/char-predicates-inl.h"
 #include "src/factory.h"
 #include "src/isolate.h"
 #include "src/objects-inl.h"
@@ skipping 1673 matching lines @@
 
 void RegExpBuilder::AddTerm(RegExpTree* term) {
   FlushText();
   terms_.Add(term, zone());
   LAST(ADD_ATOM);
 }
 
 
 void RegExpBuilder::AddAssertion(RegExpTree* assert) {
   FlushText();
+  if (terms_.length() > 0 && terms_.last()->IsAssertion()) {
+    // Omit repeated assertions of the same type.
+    RegExpAssertion* last = terms_.last()->AsAssertion();
+    RegExpAssertion* next = assert->AsAssertion();
+    if (last->assertion_type() == next->assertion_type()) return;
+  }
   terms_.Add(assert, zone());
   LAST(ADD_ASSERT);
 }
 
 
 void RegExpBuilder::NewAlternative() { FlushTerms(); }
 
 
 void RegExpBuilder::FlushTerms() {
   FlushText();
@@ skipping 100 matching lines @@
     return false;
   }
   terms_.Add(new (zone()) RegExpQuantifier(min, max, quantifier_type, atom),
              zone());
   LAST(ADD_TERM);
   return true;
 }
 
 }  // namespace internal
 }  // namespace v8