[llvm] [SystemZ] Avoid repeated hash lookups (NFC) (PR #126005)

[Nikita Popov via llvm-commits]

================
@@ -6173,8 +6173,9 @@ SystemZTargetLowering::buildVector(SelectionDAG &DAG, const SDLoc &DL, EVT VT,
     for (unsigned I = 0; I < NumElements; ++I)
       if (isVectorElementLoad(Elems[I])) {
         SDNode *Ld = Elems[I].getNode();
-        UseCounts[Ld]++;
-        if (LoadMaxUses == nullptr || UseCounts[LoadMaxUses] < UseCounts[Ld])
+        auto &Count = UseCounts[Ld];
+        ++Count;
----------------
nikic wrote:

```suggestion
        unsigned Count = ++UseCounts[Ld];
```
Maybe?

https://github.com/llvm/llvm-project/pull/126005