Minus in comment causes incredibly slow highlighting

[zostay]

Migration of issue https://github.com/vim-perl/vim-perl6/issues/21 by @timo

Description of issue

Files with comments that have many - in them are extremely slow, often aborting highlighting for the entire file.

Start a line with just # and maybe a space, then type - and see syntax highlighting get slower and slower, and eventually die completely.

[zostay]

I am not able to reproduce this problem on vim 8.0 on my machine.

[sarna]

Not able to reproduce this either, Neovim v0.4.3.