[AArch64] Minor cleanup and speedup for getVectorInstrCostHelper

If UserToExtractIdx is empty then we can skip checking the users.

Author: davemgreen

llvm/lib/Target/AArch64/AArch64TargetTransformInfo.cpp

@@ -3248,15 +3248,14 @@ InstructionCost AArch64TTIImpl::getVectorInstrCostHelper(
     // Check if the extractelement user is scalar fmul.
     auto IsUserFMulScalarTy = [](const Value *EEUser) {
       // Check if the user is scalar fmul.
-      const auto *BO = dyn_cast_if_present<BinaryOperator>(EEUser);
+      const auto *BO = dyn_cast<BinaryOperator>(EEUser);
       return BO && BO->getOpcode() == BinaryOperator::FMul &&
              !BO->getType()->isVectorTy();
     };
 
     // Check if the extract index is from lane 0 or lane equivalent to 0 for a
     // certain scalar type and a certain vector register width.
-    auto IsExtractLaneEquivalentToZero = [&](const unsigned &Idx,
-                                             const unsigned &EltSz) {
+    auto IsExtractLaneEquivalentToZero = [&](unsigned Idx, unsigned EltSz) {
       auto RegWidth =
           getRegisterBitWidth(TargetTransformInfo::RGK_FixedWidthVector)
               .getFixedValue();
@@ -3277,13 +3276,15 @@ InstructionCost AArch64TTIImpl::getVectorInstrCostHelper(
         // important.
         UserToExtractIdx[U];
       }
+      if (UserToExtractIdx.empty())
+        return false;
       for (auto &[S, U, L] : ScalarUserAndIdx) {
         for (auto *U : S->users()) {
           if (UserToExtractIdx.find(U) != UserToExtractIdx.end()) {
             auto *FMul = cast<BinaryOperator>(U);
             auto *Op0 = FMul->getOperand(0);
             auto *Op1 = FMul->getOperand(1);
-            if ((Op0 == S && Op1 == S) || (Op0 != S) || (Op1 != S)) {
+            if ((Op0 == S && Op1 == S) || Op0 != S || Op1 != S) {
               UserToExtractIdx[U] = L;
               break;
             }