Re: [PATCH] Improve BB vectorization dependence analysis

["H.J. Lu" <hjl dot tools at gmail dot com>]

On Mon, Nov 9, 2015 at 4:55 AM, Richard Biener <rguenther@suse.de> wrote:
>
> Currently BB vectorization computes all dependences inside a BB
> region and fails all vectorization if it cannot handle some of them.
>
> This is obviously not needed - BB vectorization can restrict the
> dependence tests to those that are needed to apply the load/store
> motion effectively performed by the vectorization (sinking all
> participating loads/stores to the place of the last one).
>
> With restructuring it that way it's also easy to not give up completely
> but only for the SLP instance we cannot vectorize (this gives
> a slight bump in my SPEC CPU 2006 testing to 756 vectorized basic
> block regions).
>
> But first and foremost this patch is to reduce the dependence analysis
> cost and somewhat mitigate the compile-time effects of the first patch.
>
> For fixing PR56118 only a cost model issue remains.
>
> Bootstrapped and tested on x86_64-unknown-linux-gnu, applied to trunk.
>
> Richard.
>
> 2015-11-09  Richard Biener  <rguenther@suse.de>
>
>         PR tree-optimization/56118
>         * tree-vectorizer.h (vect_find_last_scalar_stmt_in_slp): Declare.
>         * tree-vect-slp.c (vect_find_last_scalar_stmt_in_slp): Export.
>         * tree-vect-data-refs.c (vect_slp_analyze_node_dependences): New
>         function.
>         (vect_slp_analyze_data_ref_dependences): Instead of computing
>         all dependences of the region DRs just analyze the code motions
>         SLP vectorization will perform.  Remove SLP instances that
>         cannot have their store/load motions applied.
>         (vect_analyze_data_refs): Allow DRs without a vectype
>         in BB vectorization.
>

This caused:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68492


H.J.