[llvm-dev] (Thin)LTO llvm build
Teresa Johnson via llvm-dev
llvm-dev at lists.llvm.org
Mon Sep 26 08:16:57 PDT 2016
On Mon, Sep 26, 2016 at 8:08 AM, Carsten Mattner <carstenmattner at gmail.com>
> On Mon, Sep 26, 2016 at 4:25 PM, Teresa Johnson <tejohnson at google.com>
> > 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
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?
> > 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
> >> > 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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