[llvm-dev] failing to optimize boolean ops on cmps

Hal Finkel via llvm-dev llvm-dev at lists.llvm.org
Fri Jul 14 11:46:11 PDT 2017

On 07/14/2017 01:38 PM, Daniel Berlin wrote:
>     Not sure about this last part. It is really going to require work
>     by us to rewrite things. :-) In the mean time, I think we should
>     go ahead with this.
> FWIW: My problem is, when put in this framework, we will repeatedly 
> make this same decision, this same way, again and again, and never 
> actually get even started on fixing it :)
> IE "it's just another small patch!"

You're correct. However, as I'm sure you're aware, developer time is not 
directly transferable in a way that makes any other decision optimal. 
It's not like blocking all improvements to InstCombine will cause a 
movement to appear to rewrite InstCombine. It will only cause a shrink 
in the pool of developers with recent experience working on InstCombine 
(and a lot of out-of-tree patches). Frankly, we don't even have a 
concrete plan for how we'd do this, or even a target design, and that's 
the first item on the critical path to a rewrite. We should start an RFC 
and iterate on this until we have a concrete plan and migration plan.


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

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