serviceability agent : problems when using gcc LTO (link time optimization)

[Baesken, Matthias]

Hello  Magnus and Aleksei,  thanks for the input .

The times you  provided really look like they make a big difference  at least for people  often  building   minimal-vm  .
Guess I have to measure myself a bit  (maybe the difference is not that big on our linux s390x / ppc64(le) ) .

>
> If the change to enable lto by default is proposed, what would be the
> recommended strategy for development?
>

Probably  we should a)   do not enable it by default but just make sure it can be enabled easily and works  for  the minimal-vm     or  b)  take it easy to disable it for local development.

Best regards, Matthias



> 
> Magnus, Matthias,
> 
> for me, lto is a little heavyweight for development. x86_64 build time
> with gcc 7:
> 
> Server 1m32.484s
> Server+Minimal 1m42.166s
> Server+Minimal (--with-jvm-features="link-time-opt") 5m29.422s
> 
> If the change to enable lto by default is proposed, what would be the
> recommended strategy for development?
> 
> For ARM32 Minimal, please keep in mind that it's not uncommon to disable
> LTO plugin in commodity ARM32 gcc compiler distributions, so for some it
> does not matter what settings we have in OpenJDK. I believe there could
> be other reasons for that on top of build time (bugs?).
>