On Mon, Jan 17, 2022 at 8:56 PM Andrew MacLeod via Gcc-patches <gcc-patches@gcc.gnu.org> wrote: > > As mentioned in the PR, this demonstrates the potentially quadratic > performance behaviour of adding transitive relations over a series of > cascading calculations. > > As the lookup in a basic block is also linear in nature, I think for > this release it makes sense to simply limit the number of relations we > can register in any given block. > > I compiled all the c++ files in gcc, and there was only one BB in > fold-const that had more than 30 relations.. and it was a smaller case > of this sort of transitive behaviour.. and it capped out at 120 relations. > > I added a new --param, and defaulted it to 200. It has a range of > 0-9999, choosing 0 would in effect turn off relations.. which is also > handy. Caveat: this flag does not affect equivalences since they are > processed in a completely different way. > > I ran the testcase with the max 9999 and it finished fine. > > I couldn't create a simple/smallish testcase to run, so I didn't > include one. > > Bootstraps on x86_64-pc-linux-gnu with no regressions. OK for trunk?
OK. Thanks, Richard. > Andrew >
