On Mon, Jul 18, 2016 at 1:56 PM, Segher Boessenkool <seg...@kernel.crashing.org> wrote: > Hi Bill, > > On Fri, Jul 15, 2016 at 08:55:08AM -0500, Bill Schmidt wrote: >> This patch is a follow-up to Richard's patch of >> https://gcc.gnu.org/ml/gcc-patches/2016-06/msg00584.html. The cost of a >> vec_construct (initialization of an N-way vector by N scalars) is too low, >> which can cause too-aggressive vectorization in particular for N=8 or >> higher. Richard changed the default cost to N-1, which is generally >> sensible. For powerpc I am going with a slightly higher cost of N, which >> will keep us from being less conservative than the previous values when N=2. > >> In any case, the purpose of this patch is simply to avoid vectorizing >> things we shouldn't when we've undercounted the cost of a vec_construct. >> Bootstrapped and tested on powerpc64le-unknown-linux-gnu with no >> regressions (hence the vectorization decisions in the test suite have >> not changed). Is this ok for trunk? > > Do you also have a testcase where it does matter? It would be good to > add that, then. Or is it fixing a regression? > > I know nothing about the cost model, so someone else will have to review, > or I can just say "okay" ;-)
You can maybe look at gcc.dg/vect/slp-4[35].c (and run it with the cost model enabled). Richard. > > Segher
