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

Daniel Berlin via llvm-dev llvm-dev at lists.llvm.org
Sat Jul 15 13:09:20 PDT 2017

Which is, of course, precisely why I didn't suggest that, it was Hal's
straw man.

On Sat, Jul 15, 2017, 12:26 PM Philip Reames <listmail at philipreames.com>

> On 07/14/2017 11:46 AM, Hal Finkel via llvm-dev wrote:
> 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.
> Just want to chime in here in support of what Hal said.  I strongly
> believe we should not block incremental progress unless we have a plan in
> place for a better design.  In particular, part of being able to come up
> with a better design is having multiple people with recent knowledge of the
> system which needs replaced and stopping evolution of the old system by
> definition inhibits having such a group of people.
> Philip
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