[llvm-dev] LLVM Pass Managers

[Son Tuan VU via llvm-dev]

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.html
>
> 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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