[LLVMdev] [llvm] r187267 - SLP Vectorier: Don't vectorize really short chains because they are already handled by the SelectionDAG store-vectorizer, which does a better job in deciding when to vectorize.

[Daniel Berlin]

Hey Nadav,
I'd humbly suggest that rather than use 3 directly, you should add a shared
constant between these two passes, so when one changes, the other doesn't
need to be updated. It would also ensure this bit of info about what needs
to be updated isn't only contained in the comments..

On Fri, Jul 26, 2013 at 4:07 PM, Nadav Rotem <nrotem at apple.com> wrote:

> Author: nadav
> Date: Fri Jul 26 18:07:55 2013
> New Revision: 187267
>
> URL: http://llvm.org/viewvc/llvm-project?rev=187267&view=rev
> Log:
> SLP Vectorier:  Don't vectorize really short chains because they are
> already handled by the SelectionDAG store-vectorizer, which does a better
> job in deciding when to vectorize.



>
> Modified: llvm/trunk/lib/Transforms/Vectorize/SLPVectorizer.cpp
> URL:
> http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Vectorize/SLPVectorizer.cpp?rev=187267&r1=187266&r2=187267&view=diff
>
> ==============================================================================
> --- llvm/trunk/lib/Transforms/Vectorize/SLPVectorizer.cpp (original)
> +++ llvm/trunk/lib/Transforms/Vectorize/SLPVectorizer.cpp Fri Jul 26
> 18:07:55 2013
> @@ -898,8 +898,12 @@ int BoUpSLP::getTreeCost() {
>    DEBUG(dbgs() << "SLP: Calculating cost for tree of size " <<
>          VectorizableTree.size() << ".\n");
>
> -  if (!VectorizableTree.size()) {
> -    assert(!ExternalUses.size() && "We should not have any external
> users");
> +  // Don't vectorize tiny trees. Small load/store chains or consecutive
> stores
> +  // of constants will be vectoried in SelectionDAG in
> MergeConsecutiveStores.
> +  if (VectorizableTree.size() < 3) {
> +    if (!VectorizableTree.size()) {
> +      assert(!ExternalUses.size() && "We should not have any external
> users");
> +    }
>      return 0;
>    }
>
>
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