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

[Eric Christopher]

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
>>>>>>>
>>>>>>> EMAIL PREFERENCES
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>>>>>>>
>>>>>>>
>>>>>>>
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