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

[Chandler Carruth]

Actually, even this could be done cleanly.

You could change the *pass* to accept the generic predicate in this case,
and add one unpredicated version to the pipeline and add a predicated form
later.

I'm essentially trying to lift the predicate logic out of the pass
management machinery and into the pass itself because that's where the
motivation for a predicate comes from.

On Wed, Apr 8, 2015 at 8:03 PM Chandler Carruth <chandlerc at google.com>
wrote:

> 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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