[PATCH] Add a callback to FunctionPass to enable skipping execution on a per-function basis

[Chandler Carruth]

Is this a real use case or a hypothetical one? Because it seems somewhat
contrived to me...

If there really is some predicate that necessitates really radically
different pass pipelines, I feel like they should be, well, two separate
pass pipelines.

On Wed, Apr 8, 2015 at 7:54 PM Eric Christopher <echristo at gmail.com> wrote:

> Optnone, IMO, needs to be replaced by something less terrible.
>
> I'm not sure how this is going to work with the "I want to run the first
> cfgcleanup unconditionally, but not the second" without tying the
> subtargets to things like shouldRunCfgCleanup2().
>
> On Wed, Apr 8, 2015, 7:38 PM Sean Silva <chisophugis at gmail.com> wrote:
>
>> Adding Paul as this seems related to optnone.
>>
>> On Wed, Apr 8, 2015 at 7:31 PM, Chandler Carruth <chandlerc at gmail.com>
>> wrote:
>>
>>> I feel like we could do something much simpler than this. This feeling
>>> is predicated on one primary theory: most passes will run for most
>>> subtargets. Put another way, there will only be a small number of passes
>>> that we actually want to opt out of on a per-subtarget basis.
>>>
>>> If we think that's likely to be the case, here is an alternative
>>> suggestion:
>>>
>>> - Add bool-returning predicates for each pass to the subtarget base
>>> class (eg, "isIfConversionProfitable()") with the expected default ("true").
>>> - Override these for the subtargets that want to opt out.
>>> - Change the pass to directly get the subtarget, query it, and bail
>>> without doing anything if it gets "false".
>>>
>>> From looking at and thinking about if-conversion at least, this seems
>>> nicer to me. It makes someone working on the pass aware that there are
>>> subtarget profitability concerns, and it makes it very clear that we are
>>> *running* all of the passes, just that some have no effect on certain
>>> subtargets.
>>>
>>> This also matches how an optimization pass should query the function for
>>> the 'noopt' attribute and bail.
>>>
>>> Thoughts?
>>>
>>
>>>
>>> http://reviews.llvm.org/D8717
>>>
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