On 9/7/26 8:43 AM, [email protected] wrote:
From: Kyrylo Tkachov <[email protected]>
As promised elsewhere, I've accumulated a number of cleanups and modernisations
of RTL ifcvt while working on the noce_convert_multiple_sets improvements.
Now that some of the new functionality has landed I'd like to get these
cleanups in. They are all NFCs: cleaning up comments, factoring out
bookkeeping duplicate code, moving the noce transforms into a bit more
structured table-driven form, using some more modern C++ idioms,
using auto vecs and bitmaps and stuff like that.
They should make it easier to add more transforms in the future.
Bootstrapped and tested on aarch64-none-linux-gnu.
I hate to add more complexity to something like this, but Shreya and I
are nearly ready to embark on cleanups in here too.
Right now we have all these noce_try_* routines that can synthesize a
branchless sequence. The first one that has a lower cost than a branch
wins, even if there were perhaps other approaches that would be even better.
Worse yet, we have scenarios today where different targets want
radically different sequences and it's painful to transform one into the
other. So any static ordering is doomed to make some target unhappy
from a performance standpoint.
So the thinking was to have the noce_try_* routines return their
sequence, costing and perhaps other data in a structure. The caller
would iterate through all the routines, keeping the best one so far.
Once the best is found, then we'd emit the sequence into the IL and
throw away the rest.
If that's easily rolled into your changes, great. If not, I'd like to
land your changes first since they're likely far more extensive than
what Shreya and I were contemplating.
Jeff
