[PATCH] D142270: [ValueTracking] Add tests for known bits after common BMI pattern (blsmsk/blsi); NFC

[Noah Goldstein via Phabricator via llvm-commits]

goldstein.w.n added inline comments.


================
Comment at: llvm/test/Analysis/ValueTracking/knownbits-bmi-pattern.ll:268
+
+define <2 x i1> @blsmsk_signed_is_false_assume_vec(<2 x i32> %x) {
+; CHECK-LABEL: @blsmsk_signed_is_false_assume_vec(
----------------
nikic wrote:
> goldstein.w.n wrote:
> > nikic wrote:
> > > FWIW, I would remove all but one of these vector assume tests. They don't really add anything in a world where we just don't support vector assumes. (If we were to add support for them, that would get separate test coverage, and I doubt the canonical pattern we'd require for them would look like what you're doing here -- we'd probably want an assume over an and reduction.)
> > > FWIW, I would remove all but one of these vector assume tests. They don't really add anything in a world where we just don't support vector assumes. (If we were to add support for them, that would get separate test coverage, and I doubt the canonical pattern we'd require for them would look like what you're doing here -- we'd probably want an assume over an and reduction.)
> > 
> > Removed all but 2, one for `blsi` and one for `blsmsk` (one for `add_eval` and one for `cmp_eq`).
> > 
> > Unrelated but I see you have a page tracking llvm build times. Do you know what the fastest build flags are for building clang itself (for development/rebuilding, don't care about executable perf, just want it to build v fast)?
> > 
> > Unrelated but I see you have a page tracking llvm build times.
> 
> Note that these are build times of other software when compiled with clang, not time to build clang :)
> 
> I did actually start to track time to build clang recently, resulting in this fun graph (on a 6 core server): https://llvm-compile-time-tracker.com/graphs.php?stat=wall-time&startDate=2023-01-22&bench=clang Thanks to ccache, build times tend to jump between 40 seconds and 25 minutes.
> 
> > Do you know what the fastest build flags are for building clang itself (for development/rebuilding, don't care about executable perf, just want it to build v fast)?
> 
> Not really. It would probably be an unoptimized build without debug info, but if you also want to run tests, it will be slower overall.
> 
> I'm personally using release+asserts builds with lld and ccache. Only strong recommendation I have is to not use debug builds outside exceptional circumstances. They are miserable on so many levels, and you're almost always better served using `-debug` logging instead.
> > Unrelated but I see you have a page tracking llvm build times.
> 
> Note that these are build times of other software when compiled with clang, not time to build clang :)
> 
> I did actually start to track time to build clang recently, resulting in this fun graph (on a 6 core server): https://llvm-compile-time-tracker.com/graphs.php?stat=wall-time&startDate=2023-01-22&bench=clang Thanks to ccache, build times tend to jump between 40 seconds and 25 minutes.
> 
> > Do you know what the fastest build flags are for building clang itself (for development/rebuilding, don't care about executable perf, just want it to build v fast)?
> 
> Not really. It would probably be an unoptimized build without debug info, but if you also want to run tests, it will be slower overall.
> 
> I'm personally using release+asserts builds with lld and ccache. Only strong recommendation I have is to not use debug builds outside exceptional circumstances. They are miserable on so many levels, and you're almost always better served using `-debug` logging instead.

I see, I do basically the same but `-O1` instead of `release` to make things a bit faster.

It might be useful to add a flag `--build-fast` that has some passes (like elim alloca that AFAICT make things faster) but is only trying to get the build done as fast a possible rather than optimizing. Might save a handful of dev time.

Thanks for the info :)


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  https://reviews.llvm.org/D142270/new/

https://reviews.llvm.org/D142270