[CostModel] Replace ShuffleKind::SK_Alternate with ShuffleKind::SK_Select (PR33744)

As discussed on PR33744, this patch relaxes ShuffleKind::SK_Alternate which requires shuffle masks to only match an alternating pattern from its 2 sources:

e.g. v4f32: <0,5,2,7> or <4,1,6,3>

This seems far too restrictive as most SIMD hardware which will implement it using a general blend/bit-select instruction, so replaces it with SK_Select, permitting elements from either source as long as they are inline:

e.g. v4f32: <0,5,2,7>, <4,1,6,3>, <0,1,6,7>, <4,1,2,3> etc.

This initial patch just updates the name and cost model shuffle mask analysis, later patch reviews will update SLP to better utilise this - it still limits itself to SK_Alternate style patterns.

Differential Revision: https://reviews.llvm.org/D47985

llvm-svn: 334513

1 files changed, 2 insertions, 3 deletions

diff --git a/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp b/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
index fb7c7e9eb59..4eff2485118 100644
--- a/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
+++ b/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
@@ -313,7 +313,7 @@ isShuffle(ArrayRef<Value *> VL) {
   if ((CommonShuffleMode == FirstAlternate ||
        CommonShuffleMode == SecondAlternate) &&
       Vec2)
-    return TargetTransformInfo::SK_Alternate;
+    return TargetTransformInfo::SK_Select;
   // If Vec2 was never used, we have a permutation of a single vector, otherwise
   // we have permutation of 2 vectors.
   return Vec2 ? TargetTransformInfo::SK_PermuteTwoSrc
@@ -2461,8 +2461,7 @@ int BoUpSLP::getEntryCost(TreeEntry *E) {
       Instruction *I1 = cast<Instruction>(VL[1]);
       VecCost +=
           TTI->getArithmeticInstrCost(I1->getOpcode(), VecTy, Op1VK, Op2VK);
-      VecCost +=
-          TTI->getShuffleCost(TargetTransformInfo::SK_Alternate, VecTy, 0);
+      VecCost += TTI->getShuffleCost(TargetTransformInfo::SK_Select, VecTy, 0);
       return ReuseShuffleCost + VecCost - ScalarCost;
     }
     default: