llvm dev - Feb 2021 - LLVM data structures between modules

If you want to do cross-file optimization, you're looking for/want to use
something like LTO or ThinLTO. (see, for instance, the whole program
devirtualization work done with ThinLTO recently)

On Wed, Feb 24, 2021 at 12:28 PM Mohannad Ismail via llvm-dev <
llvm-dev at lists.llvm.org> wrote:
> Greetings everyone,
>
> I currently have a pass (Pass 2) that does some transformations. What I
> want to do is to have a pass (Pass 1) that runs before Pass 2, collects
> some IR information, stores it in a data structure and passes the data
> structure to Pass 2 so that I can use it for specific transformations. I
> think this can be done with getAnalysisUsage, but I'm not sure how. I
would
> like to know how to do that exactly, if it's possible.
>
> Another thing, and this is the tricky part, is that I want Pass 1 to run
> on all the source files I have first before Pass 2 runs and pass a
> collective data structure to Pass 2. In other words, I want Pass 1 to run
> across all the modules and source files first, collect information, pass it
> to Pass 2 then Pass 2 runs. Is there a way to tell LLVM to do this type of
> "double compilation"?
>
> Hope I was able to explain this well enough. Please let me know if I
> wasn't clear or if you have any questions. Thank you very much!
>
> Best regards,
> Mohannad Ismail
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
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Thank you for your reply!

Correct me if I'm wrong, but doesn't LTO kick in after the compilation
phase? My current pass makes instrumentations and the pass I want to run
before it won't make any instrumentations. So what I am thinking is that
one would be an analysis pass and the other would be a transformation
pass.
>From what I understand, instrumentation passes run first before
optimization and linking, thus LTO might not help with that. Do I need to
convert my passes to be optimization passes to take advantage of LTO? How
do I do that? Thank you for your help and support!

On Wed, Feb 24, 2021 at 4:01 PM David Blaikie <dblaikie at gmail.com>
wrote:
> If you want to do cross-file optimization, you're looking for/want to
use
> something like LTO or ThinLTO. (see, for instance, the whole program
> devirtualization work done with ThinLTO recently)
>
> On Wed, Feb 24, 2021 at 12:28 PM Mohannad Ismail via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
>
>> Greetings everyone,
>>
>> I currently have a pass (Pass 2) that does some transformations. What I
>> want to do is to have a pass (Pass 1) that runs before Pass 2, collects
>> some IR information, stores it in a data structure and passes the data
>> structure to Pass 2 so that I can use it for specific transformations.
I
>> think this can be done with getAnalysisUsage, but I'm not sure how.
I would
>> like to know how to do that exactly, if it's possible.
>>
>> Another thing, and this is the tricky part, is that I want Pass 1 to
run
>> on all the source files I have first before Pass 2 runs and pass a
>> collective data structure to Pass 2. In other words, I want Pass 1 to
run
>> across all the modules and source files first, collect information,
pass it
>> to Pass 2 then Pass 2 runs. Is there a way to tell LLVM to do this type
of
>> "double compilation"?
>>
>> Hope I was able to explain this well enough. Please let me know if I
>> wasn't clear or if you have any questions. Thank you very much!
>>
>> Best regards,
>> Mohannad Ismail
>> _______________________________________________
>> LLVM Developers mailing list
>> llvm-dev at lists.llvm.org
>> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>
>
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