[Bug tree-optimization/68707] [6 Regression] testcase gcc.dg/vect/O3-pr36098.c vectorized using VEC_PERM_EXPR rather than VEC_LOAD_LANES

alalaw01 at gcc dot gnu.org gcc-bugzilla@gcc.gnu.org
Mon Dec 14 15:44:00 GMT 2015


https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68707

--- Comment #13 from alalaw01 at gcc dot gnu.org ---
Hmmm, I realize a "definite" codegen improvement was maybe a bad choice of
wording. A "substantial" (albeit uncertain!) improvement, may have been more
accurate...

However, yes it looks like we want that patch (indeed, it still helps even when
we up the cost of permute operations and drop the -fno-vect-cost-model) - so
thanks, Richard. We'll clean up the testisms in due course.

In the longer term, is the issue here, that we aren't comparing costs of SLP vs
load-lanes, right? We merely compare the cost of whichever of those
vectorization strategies we favour, permutes et al, vs leaving it in scalar
code?


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