Re: Vectorization, SIMD

[Po Lu]

Óscar Fuentes via "Emacs development discussions." <emacs-devel@gnu.org>
writes:

> Did you try an Emacs build with auto-vectorization turned on? Some
> benchmark that theoretically could benefit from it.
>
> IIRC, hand-coded vectorization reportedly had an impact of orders of
> magnitude on some character-manipulation tasks, such as text
> searching.

Auto-vectorization is already enabled by default in the previous three
releases of GCC.  It is quite conservative and tries to minimalize the
code size penalty incurred by vectorization which is probably TRT in
the context of Emacs.

The only area where vectorization has had an impact in Emacs that I
personally recall is the Android font backend's compositing routines,
which even GCC 4.6.x is capable of vectorizing satisfactorily.
(Auto-vectorization is always enabled on Android.)  Still I was
ultimately compelled to vectorize it manually on NEON-enabled systems in
the interests of unoptimized configurations.