[llvm] [AArch64][TTI] Fix extract cost for scalar fmul users (PR #212739)

[Alexey Bataev via llvm-commits]

================
@@ -4433,7 +4433,9 @@ InstructionCost AArch64TTIImpl::getVectorInstrCostHelper(
 
     if (Scalar) {
       DenseMap<User *, unsigned> UserToExtractIdx;
-      for (auto *U : Scalar->users()) {
+      for (auto &[S, U, L] : ScalarUserAndIdx) {
+        if (S != Scalar)
+          continue;
         if (!IsUserFMulScalarTy(U))
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alexey-bataev wrote:

```suggestion
        if (!U || !IsUserFMulScalarTy(U))
```

https://github.com/llvm/llvm-project/pull/212739