[llvm-dev] PGO optimization using llvm

[Teresa Johnson via llvm-dev]

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
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>


-- 
Teresa Johnson |  Software Engineer |  tejohnson at google.com |
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