On 29/04/2020 22:15, Sven Barth via fpc-devel wrote:
Assuming we want to have support for constant evaluation of functions (and I do admit that sometimes that is a really nice to have), I don't really see a way around marking such functions somehow, cause otherwise we'd have to store the node trees of all functions that we detect as pure in the PPU.
That and also attempting to propagate or evaluate every single function you come across will make the compiler prohibitively slow. Inline functions benefit most from constant propagation because a copy of the node tree exists and you can often cut away entire branches based on the propagation of constant input parameters.
Pure functions are a slightly tricky one because there is a lot of overlap with inline functions and constant propagation, and yet there are concepts that aren't covered by either, such as 'promotion' of pure function calls outside of loops and assignment of pure function results to compile-time constants. Also, pure functions can be recursive, like with the factorial function, but there will have to be safeguards against infinite loops or other constructs designed to break the compiler in that regard (e.g. the Ackermann Function).
I'm sure others can come up with uses for pure functions. Gareth aka. Kit -- This email has been checked for viruses by Avast antivirus software. https://www.avast.com/antivirus _______________________________________________ fpc-devel maillist - fpc-devel@lists.freepascal.org https://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-devel
