[PATCH] D33540: [PM/ThinLTO] Port the ThinLTO pipeline (both components) to the new PM.

[Chandler Carruth via llvm-commits]

On Tue, Jun 27, 2017 at 3:29 PM Teresa Johnson via llvm-commits <
llvm-commits at lists.llvm.org> wrote:

> On Tue, Jun 27, 2017 at 3:19 PM, Tim Shen <timshen at google.com> wrote:
>
>> Clang sets lto::Config::UseNewPM. I suppose at somewheter in
>> lib/LTO/LTOBackend.cpp we should look at UseNewPM and
>> invoke buildThinLTOPreLinkDefaultPipeline, but I'm not sure where.
>>
>
> The LTOBackend is used at link time (the ThinLTO backends), and already
> invokes buildThinLTODefaultPipeline. The passes in
> buildThinLTOPreLinkDefaultPipeline are to be invoked during the compile
> (pre-link) phase, and hence I would expect either clang side or via
> something invoked to set up the compile passes from clang.
>

I'm betting we just didn't wire this up when Tim and I were going through.


>
>
>> I don't expect any more change on Clang side, though.
>>
>> On Tue, Jun 27, 2017 at 3:01 PM Chandler Carruth <chandlerc at google.com>
>> wrote:
>>
>>> I thought Tim landed something that used this? But maybe misremembering.
>>> I don't think I have a Clang patch outstanding... +Tim Shen
>>> <timshen at google.com>
>>>
>>> On Tue, Jun 27, 2017 at 2:52 PM Teresa Johnson via llvm-commits <
>>> llvm-commits at lists.llvm.org> wrote:
>>>
>>>>
>>>>
>>>> On Thu, May 25, 2017, 2:43 PM Chandler Carruth via Phabricator <
>>>> reviews at reviews.llvm.org> wrote:
>>>>
>>>>> chandlerc marked an inline comment as done.
>>>>> chandlerc added a comment.
>>>>>
>>>>> In https://reviews.llvm.org/D33540#764460, @tejohnson wrote:
>>>>>
>>>>> > > I hoisted the ThinLTO stop point pre-link above the partial
>>>>> inliner and the RPO function attr inference. Partial inlining isn't going
>>>>> to make the code smaller and it seems better to just do that once post-link.
>>>>> >
>>>>> > Added davidxl to comment on this change. It seems like doing some
>>>>> partial inlining during the pre-link for ThinLTO will have an effect on the
>>>>> importing. Also, it is pre-link (as well as post-link) in the old pass
>>>>> pipeline, so this would introduce an inconsistency between the pass
>>>>> pipelines. May be better to keep it in the same places, and evaluate the
>>>>> effect of removing it from the pre-link pass pipeline separately?
>>>>>
>>>>>
>>>>> Well, partial inliner isn't run at all yet. So my hope was it can get
>>>>> moved around later.
>>>>>
>>>>> I somewhat wanted to make the split line up with the simplification
>>>>> split that is already there in the pipeline. But if you feel strongly we
>>>>> need to keep these exactly the same, I can essentially copy the extra
>>>>> passes into the tail of the thinlto prelink stuff.
>>>>>
>>>>>
>>>>>
>>>>> ================
>>>>> Comment at: lib/Passes/PassBuilder.cpp:708
>>>>> +ModulePassManager
>>>>> +PassBuilder::buildThinLTOPreLinkDefaultPipeline(OptimizationLevel
>>>>> Level,
>>>>> +                                                bool DebugLogging) {
>>>>> ----------------
>>>>> tejohnson wrote:
>>>>> > I don't see this getting invoked.
>>>>> Yeah, the original patch had a change to Clang, but I wanted to get a
>>>>> submittable LLVM-focused version.
>>>>>
>>>>
>>>> Dehao just noticed that it still isn't be invoked, other than from the
>>>> manual pipeline setup for testing. Do you still have your clang side
>>>> changes around that you could submit? Or let me know if you prefer I add
>>>> that.
>>>> Teresa
>>>>
>>>>
>>>>> I'll add support for parsing these pipelines much like we support
>>>>> parsing 'default<O2>' and such so that we have some coverage of stuff.
>>>>>
>>>>>
>>>>> https://reviews.llvm.org/D33540
>>>>>
>>>>>
>>>>>
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>>>>
>>>
>
>
> --
> Teresa Johnson |  Software Engineer |  tejohnson at google.com |
> 408-460-2413 <(408)%20460-2413>
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