Re: [gentoo-dev] New project: LLVM

[Luca Barbato]

On 19/08/16 17:15, C Bergström wrote:
> On Fri, Aug 19, 2016 at 11:01 PM, Luca Barbato <lu_zero@g.o> wrote:
>> BTW is pathscale ready to be used as system compiler as well?
>
> I wish, but no. We have known issues when building grub2, glibc and
> the Linux kernel at the very least. Someone* did report a long time
> ago that with their unofficial port, were able to build/boot the
> NetBSD kernel.
> (*A community dev we trusted with our sources and was helping us with
> portability across platforms)
>
> The stuff with grub2 may potentially be fixed in the "near" future...
> the others are more tricky. In general if clang can do it, we have a
> strong chance as well.

I see, it is getting quite close =)

> As a philosophy - "we" aren't really trying to be the best generic
> compiler in the world. We aim more on optimizing as much for known
> targets. So if by system you mean, a compiler that would produce an
> "OS" which only runs on a single class of hardware, then yeah it could
> work at some point in the future. Specifically, on x86 we default on
> host CPU optimizations. So on newer Intel hardware it's easy to get a
> binary that won't run on AMD or older 64bit Intel.
>
> More recently on ARMv8 - we turn on processor specific tuning. So
> while it may "run", the difference between APM's mustang and Cavium
> ThunderX is pretty big and running binaries intended for A and ran on
> B would certainly take a hit.. (this is just the tip of the iceberg)

This is not a problem for Gentoo, actually sounds a good match for one
of our many use-cases =)

> For HPC codes or anything where you get loops or computationally
> complex - the gloves are off and I could see big differences... (again
> being general and maybe a bit dramatic for fun)

I started to do some decoding benchmark across compiler version some
time ago, I should try to put in the mix your compiler as well and
eventually blog about it =)

lu