[llvm] [SLP]Use getExtendedReduction cost and fix reduction cost calculations (PR #117350)

[Philip Reames via llvm-commits]

================
@@ -1620,6 +1620,14 @@ InstructionCost RISCVTTIImpl::getExtendedReductionCost(
 
   std::pair<InstructionCost, MVT> LT = getTypeLegalizationCost(ValTy);
 
+  if (Opcode == Instruction::Add && LT.second.isFixedLengthVector() &&
+      LT.second.getScalarType() == MVT::i1) {
----------------
preames wrote:

Again, missing the unsigned check.

https://github.com/llvm/llvm-project/pull/117350