Hi! On Mon, Jul 10, 2023 at 08:57:50AM -0400, Sid Maxwell via Gcc-help wrote: > I'm exploring updating a compiler built against the GCC 4.3.0 codebase to > (likely) GCC 12.3. Is there any documentation regarding API changes > between these versions affecting the machine description (.md) and other > machine-specific code? In fifteen years a lot has changed in GCC, but a (perhaps) surprising amount has stayed the same as well. Most earlier optimisations are done on the Gimple representation now, since such a higher-level representation is better suited for higher-level transformations; but most of the lower-level optimisation is still done in RTL, a representation that is much better suited for lower level things. So most stuff in .md files will still work as-is! There are some new target macros you should implement. Some just for better results, but a few will be absolutely necessary. There are some changes like constraint strings in expander definitions are frowned upon these days (just leave them out completely, instead of empty strings). And new pseudo-registers from splitters are allowed now (but this does not invalidate old code). My advice is to go through *all* internals documentation. Just skim things you find boring or uninteresting, but hopefully you will remember what is there, at least! And see what new stuff there is that you could take advantage of. There will be new failures in the testsuite, of course, and some of those will point to new features you do not implement yet. Unfortunately for many new features the testsuite is opt-in only, so you get no indication you could do better there unless you activly go looking there. Oh, and please change your backend to use LRA instead of just old reload, since we are trying to get rid of the latter. For many targets this does not need more than just flipping the switch, but testing can reveal shortcomings in your backend, or in the generic compiler as well. Good luck, and have fun! Maybe in a year or half year or whatever you can write a retrospective for us, what things were surprising, what we did well and what not, etc.? Segher
