Enabling -ftree-slp-vectorize on -O2/Os

[Richard Biener]

On Tue, May 29, 2018 at 5:24 PM Allan Sandfeld Jensen <linux@carewolf.com>
wrote:

> On Dienstag, 29. Mai 2018 16:57:56 CEST Richard Biener wrote:
> >
> > so the situation improves but isn't fully fixed (STLF issues maybe?)
> >

> That raises the question if it helps in these cases even in -O3?

That's a good question indeed.  We might end up (partly) BB vectorizing
loop bodies that we'd otherwise loop vectorize with SLP.  Benchmarking
with BB vectorization disabled at -O3+ isn't something I've done in the
past.  I'm now doing a 2-run with -march=haswell -Ofast
[-fno-tree-slp-vectorize]
for the FP benchmarks.

Note that there were some cases where disabling vectorization wholly
improved things.

> Anyway it doesn't look good for it. Did the binary size at least improve
with
> prefer-avx128, or was that also worse or insignificant?

Similar to the AVX258 results.  I guess where AVX256 applied we now simply
do two vector ops with AVX128.

Richard.


> 'Allan