[llvm-dev] (Thin)LTO llvm build

Teresa Johnson via llvm-dev
Mon, 26 Sep 2016 15:16:57 -0000

On Mon, Sep 26, 2016 at 8:08 AM, Carsten Mattner <carstenmattner at
gmail.com>
wrote:

> On Mon, Sep 26, 2016 at 4:25 PM, Teresa Johnson <tejohnson at
google.com>
> wrote:
> > No worries, thanks for the update. Teresa
>
> 2048 wasn't enough. Bumped to 4096. Only 1300 ninja targets left.
>
> Once I've been successful with this, I might try building a ThinLTO
Firefox
> or maybe Chromium,


I have built both of those successfully with ThinLTO, so they should work.


> although browsers usually have PGO profiles one
> can run for feeding back real-world exercise. Not sure if PGO can be
> combined with LTO, or if it makes sense at all...
>

Yes, absolutely! ThinLTO and PGO are largely orthogonal, but PGO will help
enable
more indirect call promotion with ThinLTO, and there is also a patch out
for review (D24638)
to use FDO to guide ThinLTO function importing heuristics.


> What would be more fun is combining ThinLTO for C code with MLton
> for SML code when building Ur/Web.
>

Interesting. I am not at all familiar with SML code/building, but
theoretically switching the C code to
use -flto=thin shouldn't affect the interaction between those two compiles.
Presumably one or both
are compiled into a library and linked in to create a final binary?

Teresa


>
> > On Mon, Sep 26, 2016, 7:16 AM Carsten Mattner <carstenmattner at
gmail.com>
> > wrote:
> >>
> >> On Mon, Sep 26, 2016 at 3:52 PM, Teresa Johnson <tejohnson at
google.com>
> >> wrote:
> >> >
> >> > ThinLTO needs to create as many temporary files as there are
input
> >> > modules to the link. From your 'ls' below, it
doesn't look like there
> is
> >> > an incredibly huge amount already created, can you check your
limits?
> >> > What is the output of:
> >> >
> >> > $ ulimit -n
> >> >
> >> > and
> >> >
> >> > $ sysctl fs.file-max
> >>
> >> Sorry for the noise, forgot to verify because I had assumed it was
> >> still set to 4096 from a similar change a couple days ago.
> >> Alas, it's just 1024 in this session. Given the # of object
files,
> >> 2048 looks more than enough. Going to re-run with that.
>



--
Teresa Johnson |  Software Engineer |  tejohnson at google.com |  408-460-2413
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