[llvm-dev] failing to optimize boolean ops on cmps
Philip Reames via llvm-dev
llvm-dev at lists.llvm.org
Sat Jul 15 13:20:46 PDT 2017
On 07/15/2017 01:09 PM, Daniel Berlin wrote:
> Which is, of course, precisely why I didn't suggest that, it was Hal's
> straw man.
Ah, sorry for the misread then. Skimming the thread, that's exactly
what I thought you *were* arguing for. Glad to know we're in agreement.
> On Sat, Jul 15, 2017, 12:26 PM Philip Reames
> <listmail at philipreames.com <mailto:listmail at philipreames.com>> wrote:
> 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.
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