Re: How to successfully use autoLIPO on GCC？

[Teresa Johnson <tejohnson@google.com>]

+davidxl who might remember the necessary options.

It's been a good 3-4 years since we've worked on or used gcc and LIPO, so
my memory is pretty stale on the usage model. I never myself worked on the
autoFDO tool, so I don't know the options there. A few comments/responses
below.

On Fri, Feb 19, 2021 at 7:55 PM ijinma <ijinma@yeah.net> wrote:

> hi, Johnson
>
>    I happened to see your patches(
> https://chromium.googlesource.com/chromiumos/third_party/gcc/+/2eee6942394ea46458d4412d613623fac806247d)
>  about autoLIPO LIPO in Google GCC. Recently, I was studying autoLIPO(
> autoFDO + lipo), but unfortunately, I encountered some problems, so I
> want to seek your help. Although the llvm thinLTO has a great advantage, I
> still want to try autoLIPO on GCC. I read the source code of the autoFDO
> tool briefly, but unfortunately I didn't find a way to enable autoLIPO.
>
>    I want to recreate autoLIPO work, and I think it's worth continuing on
> gcc. I think there should be a proper way to turn on autoLIPO, though it
> might be very old. But I'm a beginner in the compiler direction, and I'm
> not good at all of this.
>
>    So could you give me some help?
>
>    1. GCC(google gcc_4.8 ?)(
> https://chromium.googlesource.com/chromiumos/third_party/gcc/+/refs/heads/svn-mirror/google/gcc-4_8)
> and autoFDO(https://github.com/google/autofdo) versions that have been
> successfully run by autoLIPO, or some suggestions.
>

Whatever is the most recent google gcc branch would support autoFDO. I
believe that google/gcc_4.8 branch is it. Not sure about the autoFDO tool
though, David might know.

>
>    2. The usage or description of autoFDO enabling auxiliary module. That
> is, the imports file generated by AutoFDO stores the grouping algorithm
> result of the LIPO module.
>

I'm not personally familiar with usage of the autoFDO tool, but again,
David might remember.


>
>    3. Or what would I need to do if I wanted to successfully use autoLIPO
> on GCC?
>

If you want to use it with a more recent gcc I'm afraid that is probably
going to be a lot of work. I remember each time we synced our google branch
with a more recent mainline it required months of work to iron out all of
the LIPO interactions, since that wasn't supported by the main gcc branch.

Teresa


>    Looking forward to your reply!
>
>   thanks，
>   ijinma
>


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