Remove UnsafeFPMath for LLVM 21+

[mcourteaux]

No description provided.

[abadams]

Uh oh, looks like this doesn't do anything anymore. We need to figure out the correct way to enable the equivalent of -fp-contract=fast

[mcourteaux]

Feel free to take the lead on this, and close this PR if you have better changes in mind. I made this PR just in case the fix is this simple, and all the build bots go green. I'm not really in the mood for LLVM shenanigans. 🥴

[abadams]

Maybe it's this?

    options.AllowFPOpFusion = llvm::FPOpFusion::Fast;

[abadams]

Oh we already set AllowFPOpFusion. And reassociation is turned on in set_fast_fp_math. I think this PR is the correct change.

[mcourteaux]

Maybe it's this?

    options.AllowFPOpFusion = llvm::FPOpFusion::Fast;

I see: the build bots could go green, and we still lose the performance benefits of FP optimizations. I can add that line for LLVM 21+ if you think that's it.

[mcourteaux]

Oh we already set AllowFPOpFusion. And reassociation is turned on in set_fast_fp_math. I think this PR is the correct change.

Okay, then we'll wait for the bots. 😄 Thanks for chiming in so quickly.

[mcourteaux]

Any idea what's going on with correctness/extern_sort on Windows?

[mcourteaux]

It's a fluke I think. It did work on my other PR: https://buildbot.halide-lang.org/master/#/builders/267/builds/187#bb-step-39 which is rebased on this PR.

[alexreinking]

It's a fluke I think. It did work on my other PR: https://buildbot.halide-lang.org/master/#/builders/267/builds/187#bb-step-39 which is rebased on this PR.

I just triggered a rerun of that workflow. If it fails again, we can look more closely at it.

[mcourteaux]

Yeiiiy Thanks a lot! All green! Only need formal approval from someone.