[PATCH] D115800: [SLP]Do not represent splats as node with the reused scalars.

[Alexey Bataev via Phabricator via llvm-commits]

ABataev created this revision.
ABataev added reviewers: RKSimon, anton-afanasyev, dtemirbulatov.
Herald added a subscriber: hiraditya.
ABataev requested review of this revision.
Herald added a project: LLVM.

No need to represent splats as a node with the reused scalars, it may
increase the cost (currently pass just ignores extra shuffle cost and it
is still not correct).


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D115800

Files:
  llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
  llvm/test/Transforms/SLPVectorizer/X86/broadcast_long.ll


Index: llvm/test/Transforms/SLPVectorizer/X86/broadcast_long.ll
===================================================================
--- llvm/test/Transforms/SLPVectorizer/X86/broadcast_long.ll
+++ llvm/test/Transforms/SLPVectorizer/X86/broadcast_long.ll
@@ -8,7 +8,7 @@
 ; YAML-NEXT: Function:        bcast_long
 ; YAML-NEXT: Args:
 ; YAML-NEXT:  - String:          'Stores SLP vectorized with cost '
-; YAML-NEXT:  - Cost:            '-5'
+; YAML-NEXT:  - Cost:            '-4'
 ; YAML-NEXT:  - String:          ' and with tree size '
 ; YAML-NEXT:  - TreeSize:        '2'
 
Index: llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
===================================================================
--- llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
+++ llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
@@ -3524,9 +3524,14 @@
     // Check that every instruction appears once in this bundle.
     DenseMap<Value *, unsigned> UniquePositions;
     for (Value *V : VL) {
+      if (isConstant(V)) {
+        ReuseShuffleIndicies.emplace_back(
+            isa<UndefValue>(V) ? UndefMaskElem : UniqueValues.size());
+        UniqueValues.emplace_back(V);
+        continue;
+      }
       auto Res = UniquePositions.try_emplace(V, UniqueValues.size());
-      ReuseShuffleIndicies.emplace_back(isa<UndefValue>(V) ? -1
-                                                           : Res.first->second);
+      ReuseShuffleIndicies.emplace_back(Res.first->second);
       if (Res.second)
         UniqueValues.emplace_back(V);
     }
@@ -3536,6 +3541,8 @@
     } else {
       LLVM_DEBUG(dbgs() << "SLP: Shuffle for reused scalars.\n");
       if (NumUniqueScalarValues <= 1 ||
+          (NumUniqueScalarValues == 2 &&
+           any_of(UniqueValues, UndefValue::classof)) ||
           !llvm::isPowerOf2_32(NumUniqueScalarValues)) {
         LLVM_DEBUG(dbgs() << "SLP: Scalar used twice in bundle.\n");
         newTreeEntry(VL, None /*not vectorized*/, S, UserTreeIdx);
@@ -4729,7 +4736,7 @@
     if (isSplat(VL)) {
       // Found the broadcasting of the single scalar, calculate the cost as the
       // broadcast.
-      return TTI->getShuffleCost(TargetTransformInfo::SK_Broadcast, VecTy);
+      return TTI->getShuffleCost(TargetTransformInfo::SK_Broadcast, FinalVecTy);
     }
     InstructionCost ReuseShuffleCost = 0;
     if (NeedToShuffleReuses)


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