[RISCV][TTI] Fix a misuse of the getShuffleCost API [NFC]

[preames]

The getShuffleCost api, in concept, expects to only deal with non-length changing shuffles. We were failing to extend the mask appropriately before invoking it. This came up in #128537 in discussion of a potential invariant, but is otherwise unrelated.

[llvmbot]

@llvm/pr-subscribers-backend-risc-v

Author: Philip Reames (preames)

Changes

The getShuffleCost api expects to only deal with non-length changing shuffles. We were failing to extend the mask appropriately before invoking it. This came up in #128537 in discussion of a potential invariant, but is otherwise unrelated.

---

Full diff: https://github.com/llvm/llvm-project/pull/129137.diff

1 Files Affected:

• (modified) llvm/lib/Target/RISCV/RISCVTargetTransformInfo.cpp (+3-3)

diff --git a/llvm/lib/Target/RISCV/RISCVTargetTransformInfo.cpp b/llvm/lib/Target/RISCV/RISCVTargetTransformInfo.cpp
index dfea25e11c0b6..31183dd8a037c 100644
--- a/llvm/lib/Target/RISCV/RISCVTargetTransformInfo.cpp
+++ b/llvm/lib/Target/RISCV/RISCVTargetTransformInfo.cpp
@@ -481,7 +481,6 @@ InstructionCost RISCVTTIImpl::getShuffleCost(TTI::ShuffleKind Kind,
                                              ArrayRef<const Value *> Args,
                                              const Instruction *CxtI) {
   Kind = improveShuffleKindFromMask(Kind, Mask, Tp, Index, SubTp);
-
   std::pair<InstructionCost, MVT> LT = getTypeLegalizationCost(Tp);
 
   // First, handle cases where having a fixed length vector enables us to
@@ -889,11 +888,12 @@ InstructionCost RISCVTTIImpl::getInterleavedMemoryOpCost(
   if (Opcode == Instruction::Load) {
     InstructionCost Cost = MemCost;
     for (unsigned Index : Indices) {
-      FixedVectorType *SubVecTy =
+      FixedVectorType *VecTy =
           FixedVectorType::get(FVTy->getElementType(), VF * Factor);
       auto Mask = createStrideMask(Index, Factor, VF);
+      Mask.resize(VF * Factor, -1);
       InstructionCost ShuffleCost =
-          getShuffleCost(TTI::ShuffleKind::SK_PermuteSingleSrc, SubVecTy, Mask,
+          getShuffleCost(TTI::ShuffleKind::SK_PermuteSingleSrc, VecTy, Mask,
                          CostKind, 0, nullptr, {});
       Cost += ShuffleCost;
     }