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

Co-authored-by: Nikita Popov <[email protected]>

Author: kazutakahirata

llvm/lib/Target/SystemZ/SystemZISelLowering.cpp

@@ -6173,8 +6173,8 @@ 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])
+        unsigned Count = ++UseCounts[Ld];
+        if (LoadMaxUses == nullptr || UseCounts[LoadMaxUses] < Count)
           LoadMaxUses = Ld;
       }
     if (LoadMaxUses != nullptr) {