[llvm] [RISCV][TTI] Recognize CONCAT_VECTORS if a shufflevector mask is multiple insert subvector. (PR #111459)

[Craig Topper via llvm-commits]

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@@ -343,6 +343,49 @@ RISCVTTIImpl::getConstantPoolLoadCost(Type *Ty,  TTI::TargetCostKind CostKind) {
                              /*AddressSpace=*/0, CostKind);
 }
 
+InstructionCost
+RISCVTTIImpl::isMultipleInsertSubvector(VectorType *Tp, ArrayRef<int> Mask,
+                                        TTI::TargetCostKind CostKind) {
+  if (!isa<FixedVectorType>(Tp))
+    return InstructionCost::getInvalid();
+  std::pair<InstructionCost, MVT> LT = getTypeLegalizationCost(Tp);
+  if (LT.second.getScalarSizeInBits() == 1)
+    return InstructionCost::getInvalid();
+  // Try to guess SubTp.
+  for (unsigned SubVecSize = 1, E = Mask.size(); SubVecSize < E;
+       SubVecSize <<= 1) {
+    if (E % SubVecSize != 0)
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topperc wrote:

Would it be sufficient to check that Mask.size() is a power 2 before the loop since SubVecSize can only be a power 2.

https://github.com/llvm/llvm-project/pull/111459