"Retpoline", an optional compiler flag to deal with Spectre attack https://support.google.com/faqs/answer/7625886. Landing to llvm/gcc as we speak (e.g. https://reviews.llvm.org/D41723).
Virtual calls, as well as switch statements etc., are about to get more expensive.
@aras Why would you want to use them though ? does your process need the protection from an inprocess sandbox reading the memory ?
@bartwe yeah indeed, majority of people won't need that flag.