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

[Eric Christopher]

Or do you mean a predicate lambda passed during pass construction? I'd be
totally down with that.

On Wed, Apr 8, 2015, 8:17 PM Eric Christopher <echristo at gmail.com> wrote:

>
> How would that work? A parameter doesn't get us subtarget Independence in
> the pass manager construction as far as I can tell. I could be dense here
> though.
>
> On Wed, Apr 8, 2015, 8:10 PM Chandler Carruth <chandlerc at google.com>
> wrote:
>
>> I'm suggesting rather than a decorator, we use an optional predicate
>> parameter when constructing the pass. To me, that seems somewhat cleaner.
>>
>> On Wed, Apr 8, 2015 at 8:09 PM Eric Christopher <echristo at gmail.com>
>> wrote:
>>
>>> Right, I agree with this in general, but looking to avoid the weird
>>> subtarget flags that I mentioned. Perhaps we should revisit Akira's
>>> original idea of wrapping pass in a decorator if you want to pull it out of
>>> the pass manager machinery?
>>>
>>> On Wed, Apr 8, 2015, 8:04 PM Chandler Carruth <chandlerc at google.com>
>>> wrote:
>>>
>>>> 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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>>>>>>>>
>>>>>>>>
>>>>>>>>
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