On 8/3/2026 1:14 AM, Aldy Hernandez wrote:
Raise MAX_PAIRS from 1 to 2, enabling sub-ranges. This will allow us
to represent non-zero and other inequalities in a follow-up patch.
I tested how many sub-ranges would give us the most bang for the buck,
by allowing 10 sub-ranges, and seeing how many we created and used.
Even though 1 sub-range caught 91.29% of what we encountered in real
life (well, in a corpus of Fortran files from the LAPACK package), we
couldn't represent non-zero, which caused DOM to get a bunch of cases
we missed. With 2 subranges, we caught 99.63% of ranges generated,
and anything past this was useless, cause we either didn't generate
them in real life, or there was no change in generated code by having
more sub-ranges. For instance, from 3631 files, going from 2 to 3
sub-ranges caused code generation changes in 4 files (all rotmg*).
Going past 3, produced zero effect.
I also benchmarked LAPACK and the GSL package for jump threading
changes as well as VRP constant propagation. For LAPACK, we got 0.31%
more jump threading opportunities, and for GSL 1.10%. For VRP it was
the opposite, LAPACK got 0.48% more constants propagated, whereas GSL
got a mere 0.26% boost.
This may not seem like much, but just being able to represent the
inverse of a constant (e.g. nonzero) closes the gap with the DOM
internal tables. With this work, we get 100% of what DOM threading
was getting with its internal tables for the LAPACK corpus. We nuked
58 of the regressions, and I believe this will fix a few PRs we had
open for nonzero folding, as well as some signed zero missed
optimizations.
Oh, and with this patch we cause code generation differences in 2.2%
of LAPACK, and 5.48% of GSL files. I didn't dig into any of these,
but it seems other passes benefit as well. Either way, we needed a
way to represent != 0.0, which seemed like a big limitation in the
initial frange implementation, and was causing me to lose sleep in my
self-imposed break from hacking.
Tested on ppc64le: regstrap, LAPACK, GSL.
I often forget how many weird little things I put in DOM through the
years. Thanks for chasing this down and putting in the pieces that will
hopefully let us zap DOM in whole or at least big chunks of it.
jeff
