https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109914
--- Comment #7 from Jan Hubicka <hubicka at gcc dot gnu.org> --- The idea is to help developers to annotate i.e. binary tree search function, which he clearly knows is always to be finite, but compiler can not prove it. Intentional infinite loops with no side effects written in a convoluted ways are almost never intentional, so almost always developer can add the pure attribute based on his/her understanding of what the code really does.
