[llvm-dev] Opt Bisect layering

[David Blaikie via llvm-dev]

& now looking back at the patch-in-progress, I see it allows setting the
OptBisector/OptPassGate as suggested in (2).

If that becomes the /only/ option (ie: LLVMContext has no default
OptPassGate) then the virtual interface could be kept down in IR (though
it's still a bit questionable to have those Analysis types (Loop, Region,
CallGraphSCC) even declared in IR). Then the implementation of OptBisector
could be moved into Analysis - freely able to depend on the concrete
Analysis types.

- Dave

On Thu, Mar 29, 2018 at 2:01 PM David Blaikie <dblaikie at gmail.com> wrote:

> So... looking at OptBisect, I have a few thoughts:
>
> 1) what's the purpose of the virtual interface/OptPassGate? I'm guessing
> maybe that worked around the circular referencing in these APIs? hmm, no, I
> suppose that wouldn't work/be relevant here.
>
> 2) Why is OptBisector a ManagedStatic? That seems pretty antithetical to
> the role of LLVMContext. When/why would a user be bisecting over multiple
> LLVMContexts? & even then, maybe it'd be more suitable for that grouping
> (the scope for the bisection) to be API driven - passing the bisector into
> the LLVMContext ctor to define the set of contexts that share a bisector?
>
> On Wed, Mar 21, 2018 at 10:20 PM Yevgeny Rouban via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
>
>> Andrew,
>>
>> I would not make the caller pass the description of the IR unit. That is
>> because it would result in the description generated every time even if
>> OptBisect is disabled. Description generation is not very chip.
>> Thinking on the OptBisect extension, I believe passing the units are the
>> right choice because OptPassGates may use them to make pass skipping
>> decisions.
>>
>> -Yevgeny Rouban
>> -----------------------------------------------------------
>>
>> *From:* llvm-dev [mailto:llvm-dev-bounces at lists.llvm.org
>> <llvm-dev-bounces at lists.llvm.org>] *On Behalf Of *Kaylor, Andrew via llvm
>> -dev
>> *Sent:* Thursday, March 22, 2018 3:52 AM
>> *To:* David Blaikie <dblaikie at gmail.com>; llvm-dev <llvm-dev at lists.llvm
>> .org>; Friedman, Eli <efriedma at codeaurora.org>
>> *Subject:* Re: [llvm-dev] Opt Bisect layering
>>
>>
>>
>> There is a patch under review right now from someone who wants to provide
>> a mechanism to replace OptBisect as the pass gate keeping mechanism.
>>
>>
>>
>> https://reviews.llvm.org/D44464
>>
>>
>>
>> Possibly we could take this opportunity to move OptBisect to a different
>> layer, though I don’t know where else it would belong.
>>
>>
>>
>> The other possibility is that we could have the caller pass in a
>> description instead of a pointer to the pass and the IR unit. OptBisect
>> isn’t doing anything with them other than building a string for output.
>>
>>
>>
>> -Andy
>>
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>
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