[llvm-dev] Heads-up: Handling target-specific intrinsics in InstCombine

[Hal Finkel via llvm-dev]

On 6/29/20 7:29 AM, Nicolai Hähnle via llvm-dev wrote:
> Hello,
>
> this mail is to raise awareness of https://reviews.llvm.org/D81728,
> which is substantial enough of a conceptual change that it should
> probably at least be mentioned in llvm-dev.
>
> InstCombine has dealt with target-specific intrinsics for a long time,
> since its fix-point iteration is arguably the right place to do so. A
> downside is that there's a pull to add an increasing amount of code
> into lib/Transforms/InstCombine/ that really is target-specific.
>
> What the aforementioned change does is provide a target hook via
> TargetTransformInfo, and move the handling of all target intrinsics
> for InstCombine purposes into the corresponding lib/Target/$foo/
> directory via the hook, thus cleaning up the core of InstCombine.
>
> Cheers,
> Nicolai


I said this on the review, but to repeat it here, I think that this is a 
good idea. We should allow targets to customize the behavior of the 
optimizer with respect to target-specific intrinsics using code in the 
target, not code spread throughout the optimizer. We now do this kind of 
thing using TTI in many other places, and we should do it here too.

  -Hal


-- 
Hal Finkel
Lead, Compiler Technology and Programming Languages
Leadership Computing Facility
Argonne National Laboratory