[Mesa-dev] [PATCH 21/29] mesa: stop going behind the user's back wrt sse4.1 optimisations

[Matt Turner]

On Tue, Jul 29, 2014 at 3:54 PM, Emil Velikov <emil.l.velikov at gmail.com> wrote:
> If the user/builder has a setup capable of using sse4.1 it's their
> responsibility to enable it.
>
> Let's unconditionally include main/streaming-load-memcpy.c, as it
> already features a ifdef __SSE4_1__ check and add a stub implementation
> for people that don't have -msse4.1 enabled at compile-time.
>
> This resolves undefined references to _mesa_streaming_load_memcpy for
> the Android build and compilers not capable of sse4.1 optimizations.
>
> Note: if your compiler is capable of -msse4.1 and you are interested
> in using such optimisations, enable them explicitly.

The reason we build this file with -msse4.1 explicitly is because
distributions build things for the lowest common denominator but we
still want this code to be enabled (via a runtime check for SSE 4.1).

If we do this, distributions building with typical CFLAGS won't get
this optimization. That's not what we want.

What's the problem with the current solution -- that the Android build
system doesn't let you build this file with -msse4.1?