On Feb 10, 2017 7:44 AM, "Ryan B" <public@ryanb.org> wrote:
even on modern hardware, fontifying still hangs my emacs for 5-10s on long lines, e.g. 10k-20k characters, whenever they appear.

I've filled a bug report with a minimal test case for this here:

https://debbugs.gnu.org/cgi/bugreport.cgi?bug=25682