[Bug tree-optimization/83651] [7/8 regression] 20% slowdown of linux kernel AES cipher

[aldyh at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83651

Aldy Hernandez <aldyh at gcc dot gnu.org> changed:

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--- Comment #3 from Aldy Hernandez <aldyh at gcc dot gnu.org> ---
(In reply to Arnd Bergmann from comment #0)

> If there is enough interest in addressing the slowdown, it should be
> possible to create a version of the kernel AES implementation that can be
> run in user space, as the current method of reproducing the results is
> fairly tedious.

I would say that a 20% slowdown is significant enough that we should definitely
look into this.  A user space version would help immensely here.

> The source code is apparently derived from a common source, but has evolved
> in different ways, and the version from the kernel appears to be much faster
> overall. 

It looks like you have various benchmarks based on different code bases.  This
is not good for reproduceability and diagnosing the problem.  Could we settle
on one, and ideally a (simple) user space version?  This will drastically
increase the likelihood of finding a solution :).

Also, is this a GCC 8 regression?  It looks like in most of the benchmarks you
post, GCC 8 performs pretty close to 4.x.  Again, settling on one benchmark,
preferably in user space, would really help.

Thanks.