llvm dev - Apr 2019 - PGO optimization using llvm

Hi,



We are using clang based compiler for our android build system.

We plan to enable the PGO (profile guided optimization ) for some of our
android modules



I would like to have some understanding on the way that the PGO profiles
are being used by the clang compiler.

As I understand Profile guidance enables the compiler to make better
optimization decisions by using knowledge about how the program actually
runs.

With this profile information, the compiler can do a better job of inlining
functions, ordering basic blocks, allocating registers, and so on.



So I would like to know if the clang based compiler in android will use
these profiles for making better decisions on inlining or register
allocations ?



But when I went through the clang documentation, right now the pgo profiles
can be used for block reordering but could not find reference as to whether
it helps the compiler

to take any other optimized decision .

https://clang.llvm.org/docs/UsersManual.html#profile-guided-optimization



Can you please help me to get this information if it’s something that clang
has yet to support with regards to PGO generated profiles.



Best Regards

Priyanka
-------------- next part --------------
An HTML attachment was scrubbed...
URL:
<http://lists.llvm.org/pipermail/llvm-dev/attachments/20190426/a177160d/attachment-0001.html>

On Sat, Apr 27, 2019 at 9:24 AM Priyanka Bose via llvm-dev <
llvm-dev at lists.llvm.org> wrote:
> Hi,
>
>
>
> We are using clang based compiler for our android build system.
>
> We plan to enable the PGO (profile guided optimization ) for some of our
> android modules
>
>
>
> I would like to have some understanding on the way that the PGO profiles
> are being used by the clang compiler.
>
> As I understand Profile guidance enables the compiler to make better
> optimization decisions by using knowledge about how the program actually
> runs.
>
> With this profile information, the compiler can do a better job of
> inlining functions, ordering basic blocks, allocating registers, and so on
> .
>
>
>
> So I would like to know if the clang based compiler in android will use
> these profiles for making better decisions on inlining or register
> allocations ?
>
Not sure on the register allocation, but definitely yes for inlining. It is
also used for a slew of other optimizations (e.g. value profiling based
indirect call promotion and memcpy optimization, partial inlining, function
layout, and misc other places.

Teresa

>
> But when I went through the clang documentation, right now the pgo
> profiles can be used for block reordering but could not find reference as
> to whether it helps the compiler
>
> to take any other optimized decision .
>
> https://clang.llvm.org/docs/UsersManual.html#profile-guided-optimization
>
>
>
> Can you please help me to get this information if it’s something that
> clang has yet to support with regards to PGO generated profiles.
>
>
>
> Best Regards
>
> Priyanka
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>

-- 
Teresa Johnson |  Software Engineer |  tejohnson at google.com |
-------------- next part --------------
An HTML attachment was scrubbed...
URL:
<http://lists.llvm.org/pipermail/llvm-dev/attachments/20190427/2a9079fe/attachment.html>