[regexp] Fold repeated assertions

src/regexp/regexp-parser.cc

Index: src/regexp/regexp-parser.cc
diff --git a/src/regexp/regexp-parser.cc b/src/regexp/regexp-parser.cc
index 1d7829a4b77d830e78d665149267055fa20f4928..33a16ef01fb2637c402d84a677c9feb3662f8fe3 100644
--- a/src/regexp/regexp-parser.cc
+++ b/src/regexp/regexp-parser.cc
@@ -1691,6 +1691,12 @@ void RegExpBuilder::AddTerm(RegExpTree* term) {
 
 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);
 }