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Re: [PATCH] Aarch64: Add simd exp/expf functions
On Wed, 2019-03-06 at 20:45 +0100, Florian Weimer wrote:
> > > Can you add assembler trampolines, so that the compiler support
> > > becomes optional, at a performance cost?
> >
> > Yuck. I suppose this is possible, but I do not want to do it.
> > The whole reason for vector functions (and for the new vector ABI)
> > is performance so adding a slow path doesn't seem to me like it is
> > worthwhile.
>
> On the other hand, it could help to get libmvec out of the door more
> quickly. I think it's not ideal that if you use an older compiler,
> you get only a subset of the glibc ABI. We can get away with it here
> because it affects an entire soname. Still it might be difficult to
> explain why applications are not portable.
If the user doesn't have gcc-9, their compiler isn't going to generate
any calls to these routines anyway. So it doesn't really matter if
they have libmvec or not if they don't have gcc-9. If a program was
compiled with gcc-9 somewhere else and then moved, then yes the new
platform might not have libmvec and there will be portability problems.
I guess if someone was building a platform with gcc-8 and the latest
glibc then it might be nice if libmvec could be built, but gcc-9 should
be released before the next glibc is released so hopefully anyone using
the latest released glibc will also use the latest gcc and have all the
necessary compiler support.
Steve Ellcey
sellcey@marvell.com