[llvm-dev] LLVM Pass Managers

[Son Tuan VU via llvm-dev]

+ Vedant: what do you think about the last point, since Debugify is also
related?

Son Tuan Vu

On Thu, Apr 19, 2018 at 6:14 PM, Philip Pfaffe <philip.pfaffe at gmail.com>
wrote:

> Hi Son,
>
> PassManagerBuilder is used to populate legacy PassManagers.  That role is
> taken over by PassBuilder for new-PM passes.
>
> Cheers,
> Philip
>
> 2018-04-18 13:40 GMT+02:00 Son Tuan VU <sontuan.vu119 at gmail.com>:
>
>> Hi Philip,
>>
>> Thank you for your reply. So what would be the right way/API to write
>> out-of-tree pass? I've been using *PassManagerBuilder*, which requires a
>> callback refering to *legacy::PassManagerBase*, so I guess this will be
>> no longer the good way to go?
>>
>> Son Tuan Vu
>>
>> On Tue, Apr 17, 2018 at 6:06 PM, Philip Pfaffe <philip.pfaffe at gmail.com>
>> wrote:
>>
>>> Hi Son,
>>>
>>> I have an answer to your first question:
>>>
>>> 1, What are the differences between *LegacyPassManager* and
>>>> *PassManager*?  I see that *opt* uses the former most of the times
>>>> while the latter is used via *PassBuilder* API when an user wants to
>>>> build her own pipeline, but I have no idea why so. What to use and when to
>>>> use it is not clear to me.
>>>>
>>> PassManager is the result of a long going effort to replace the default
>>> pass manager of opt and clang. Here's the original RFC containing the
>>> motivation: http://lists.llvm.org/pipermail/llvm-dev/2012-July/051643.ht
>>> ml
>>>
>>> LegacyPassManager is currently still the default, but we are really
>>> close to switching over the the new one. Both opt and clang have switches
>>> to enable the new one, by calling `opt -passes="...."` or `clang
>>> -fexperimental-new-pass-manager`. PassBuilder is essentially a big
>>> factory to produce PassManager and AnalysisManager objects for the passes
>>> and analyses included in core LLVM. If you develop analyses and passes, I'd
>>> suggest doing so against the new PM, especially if you plan on upstreaming
>>> your work.
>>>
>>> Cheers,
>>> Philip
>>>
>>
>>
>
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