Hmm, this all reminds me about the approach Andrew Pinski and I came up with two years ago. All in all I think it might be worth to express folding-patterns in a more abstract way. So the md-like Lisp syntax for this seems to be just stringent. We make use of such a script-language already for machine-description.
Nevertheless I doubt that we really want to have same facility for fold-const and gimple. Instead I got the impression that we would prefer to have all folding-optimizations instead in Middle-end (GIMPLE). We need folding in front-end (AST) mostly for determination of constant-expression detection. Otherwise we want to keep maximum of original AST to have best results for debugging (and even to think about having alternative FE on our middle/backend) and code-analyzers. So I doubt that we want to keep fold-const patterns similar to gimple (forward-prop) ones. Wouldn't it make more sense to move fold-const patterns completely into gimple, and having a facility in FE to ask gimple to *pre*-fold a given tree to see if a constant-expression can be achieved? Regards, Kai
