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

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).

Differential Revision: https://reviews.llvm.org/D115800
This commit is contained in:
Alexey Bataev 2021-12-10 07:43:52 -08:00
parent 417014170b
commit 6f2e087631
2 changed files with 12 additions and 3 deletions
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13
llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
View File

@ -3524,9 +3524,14 @@ void BoUpSLP::buildTree_rec(ArrayRef<Value *> VL, unsigned Depth,
// 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 @@ void BoUpSLP::buildTree_rec(ArrayRef<Value *> VL, unsigned Depth,
} 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);
@ -4729,6 +4736,8 @@ InstructionCost BoUpSLP::getEntryCost(const TreeEntry *E,
if (isSplat(VL)) {
// Found the broadcasting of the single scalar, calculate the cost as the
// broadcast.
assert(VecTy == FinalVecTy &&
"No reused scalars expected for broadcast.");
return TTI->getShuffleCost(TargetTransformInfo::SK_Broadcast, VecTy);
}
InstructionCost ReuseShuffleCost = 0;

2
llvm/test/Transforms/SLPVectorizer/X86/broadcast_long.ll
View File

@ -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'