Remove openlibm

[simonbyrne]

Thanks to @pkofod we're quite close, but there are a couple of places left:

• fastmath.jl still calls the libm in a few places
• cbrt Add Julia port of cbrt from Openlibm. #25948
• exp2 Add exp2 port of Openlibm exp2. #24859
• expm1 Julia port of Openlibm expm1. #25903
• log2 Replace log2 and log10 with Julia ports. #27137
• log10 Replace log2 and log10 with Julia ports. #27137
• rem Implement rem(float, float, RoundNearest) in Julia #42380
• modf Implement modf in Julia #42392
• fma to deal with broken system libms (test/numbers.jl fails on 32-bit platform #9847)
• _ldexp_exp

SpecialFunctions.jl also calls a few. Note however that SpecialFunctions now uses OpenLibm_jll and no longer relies on Julia providing openlibm.

• lgamma
• lgamma_r
• gamma
• erf/erfc
• besselj0/besselj1/bessly0/bessely1
• besselj
• bessely

[vchuravy]

Aren't we also convincing LLVM to call Openlibm instead of the system libm?

[simonbyrne]

Are we? I remember talking about it, but did we ever make that happen?

[vchuravy]

I can't find any reference to it in the source code so we are probably not doing that and I just remember the same discussion.
We could probably resolve the libcalls llvm will lower them to similar to what I am trying to do in #26381

[simonbyrne]

Could we get them to resolve to specific Julia methods? That would be ideal.

[Keno]

Ideally we should figure out a generic mechanism to have LLVM request a function be constant folded with the implementation we have available in the compiler.

[vchuravy]

Speculating here, but it looks like it might be possible to use `setAvailableWithName` after using `getLibFunc` http://llvm.org/doxygen/TargetLibraryInfo_8h_source.html to force a particular triple to use a different version of a library function (and it might even allow us to insert vectorised versions?) Also see https://github.com/llvm-mirror/llvm/blob/master/tools/llc/llc.cpp#L472-L478

[pkofod]

I have code for log2, log10, lgamma and remainder as well. I think _ldexp_exp as well, but it is very short either way. I just havn't really prioritized making new PRs given that the existing ones are moving rather slowly, and I have some deadlines outside of OSS.

[ararslan]

@pkofod If you get the chance I recommend just opening PRs with your changes, and if you need to be away for a while, someone who knows what they're doing can push to the branch with any necessary changes if applicable.

[giordano]

Regarding fastmath point, I have this PR still waiting for review: #24031. If it's good, I can add the missing functions

[ViralBShah]

@pkofod Would you be able to push through your PRs?

Things like SpecialFunctions should be easy to update, and the fastmath could just fallback to the system libm initially perhaps?

[pkofod]

What do you mean? If I can pr the remaining, or if the existing can be be finished soon ?

[ViralBShah]

I was actually referring to bumping the existing ones if someone needs to review or do something about those. How far do you think we are from excising the remaining ones?

[StefanKarpinski]

The above checklist with no check marks makes it look like none of this is done which I'm fairly sure it not the case at this point. @pkofod, would you mind updating the checkmarks here? Should be very satisfying since everyone knows that getting to check the boxes is why people make check lists.