Commit 2f22cd60 authored by Jan de Mooij's avatar Jan de Mooij
Browse files

Bug 1827258 part 2 - Optimize IsConcatSpreadable. r=jonco 

Use the interesting-symbol mechanism for `@@isConcatSpreadable` so that we can
add a fast path for the common case where the symbol isn't defined.

Differential Revision: https://phabricator.services.mozilla.com/D175776
parent 9845cb1d

js/src/builtin/Array.cpp

+19 −11
Original line number Diff line number Diff line
@@ -4550,21 +4550,29 @@ static bool IsConcatSpreadable(JSContext* cx, HandleValue v, bool* spreadable) { 
  }



  // Step 2.

  JS::Symbol* sym = cx->wellKnownSymbols().isConcatSpreadable;

  JSObject* holder;

  if (MOZ_UNLIKELY(

          MaybeHasInterestingSymbolProperty(cx, &v.toObject(), sym, &holder))) {

    RootedValue res(cx);

  RootedObject obj(cx, &v.toObject());

  RootedId id(cx,

              PropertyKey::Symbol(cx->wellKnownSymbols().isConcatSpreadable));

  if (!GetProperty(cx, obj, v, id, &res)) {

    RootedObject obj(cx, holder);

    Rooted<PropertyKey> key(cx, PropertyKey::Symbol(sym));

    if (!GetProperty(cx, obj, v, key, &res)) {

      return false;

    }



    // Step 3.

    if (!res.isUndefined()) {

      *spreadable = ToBoolean(res);

      return true;

    }

  }



  // Step 4.

  if (MOZ_LIKELY(v.toObject().is<ArrayObject>())) {

    *spreadable = true;

    return true;

  }

  RootedObject obj(cx, &v.toObject());

  bool isArray;

  if (!JS::IsArray(cx, obj, &isArray)) {

    return false;

js/src/vm/SymbolType.h

+3 −1
Original line number Diff line number Diff line
@@ -79,7 +79,9 @@ class Symbol 
  // symbol properties are added, so we can optimize lookups on objects that

  // don't have the BaseShape flag.

  bool isInterestingSymbol() const {

    return code_ == SymbolCode::toStringTag || code_ == SymbolCode::toPrimitive;

    return code_ == SymbolCode::toStringTag ||

           code_ == SymbolCode::toPrimitive ||

           code_ == SymbolCode::isConcatSpreadable;

  }



  // Symbol created for the #PrivateName syntax.