[2/2] selftests/powerpc: benchmarks/context_switch.c use vector instructions/types

Michael Ellerman mpe at ellerman.id.au
Wed Jul 6 00:10:09 AEST 2016

On Thu, 2016-03-03 at 23:06:40 UTC, Cyril Bur wrote:
> Currently it doesn't appear the resulting binary actually uses any Altivec
> or VSX instructions the solution is to explicitly tell GCC to use vector
> instructions and use vector types in the code.
> Part of this this issue can be GCC version specific:
> GCC 4.9.x is happy to use Altivec and VSX instructions if altivec.h is
> includedi (and possibly if vector types are used), this also means that
> 4.9.x will use VSX instructions even if only -maltivec is passed. It is
> also possible that Altivec instructions will be used even without -maltivec
> or -mabi=altivec.
> GCC 5.2.x complains about the lack of -maltivec parameter if altivec.h is
> included and will not use VSX unless -mvsx is present on commandline.
> GCC 5.3.0 has a regression that means __attribute__((__target__("no-vsx"))
> fails to build. A fix is targeted for 5.4.
> Furthermore LTO (Link Time Optimisation) doesn't play well with
> __attribute__((__target__("no-vsx")), LTO can cause GCC to forget about the
> attribute and compile with VSX instructions regardless. Be weary when
> enabling -flfo for this test.
> Signed-off-by: Cyril Bur <cyrilbur at gmail.com>

Applied to powerpc next, thanks.



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