On 6 April 2011 16:07, Hans-Peter Nilsson <hans-peter.nils...@axis.com> wrote: >> Date: Thu, 31 Mar 2011 13:39:05 +0200 >> From: Ira Rosen <ira.ro...@linaro.org> > >> This patch changes NEON's default vector size from 64 to 128 bits. > > I'm wondering, are there NEON-specific measurements to support > this change? > > A colleague of mine implemented support for 64- and 128-bit NEON > for RAPP <http://savannah.nongnu.org/projects/rapp/>, but found > that the 128-bit version was slower.
The best vector size depends on the particular target (a version of ARM) and the benchmark. The vectorizer has a cost model that allows it to fall back to 64-bit vectors if 128-bit version is not profitable (-fvect-cost-model). We plan to enhance the cost model to estimate both versions and vectorize with the most profitable vector size. For now, you can use preferred-vector-size param if needed. Having 64 as a default doesn't allow us to use different NEON instructions that use both types of vectors. Ira > > brgds, H-P >
