Thank you, Segher. One thing that might be helpful would be, as I read the current "GNU Compiler Collection Internals For gcc version 14.0.0 (pre-release)", to compare it with the version of the same document that was relevant for 4.3.0. Do you know where I might learn which version is appropriate, and where I might find it? ( https://gcc.gnu.org/onlinedocs/ only seems to have the current version.) -+- Sid On Mon, Jul 10, 2023 at 1:15 PM Segher Boessenkool < segher@xxxxxxxxxxxxxxxxxxx> wrote: > 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 >
