[llvm] [LoopInterchange] Modernize loops (NFC) (PR #146105)

[Ryotaro Kasuga via llvm-commits]

================
@@ -551,12 +551,10 @@ struct LoopInterchange {
     //
     // For the old pass manager CacheCost would be null.
     DenseMap<const Loop *, unsigned> CostMap;
-    if (CC != nullptr) {
-      const auto &LoopCosts = CC->getLoopCosts();
-      for (unsigned i = 0; i < LoopCosts.size(); i++) {
-        CostMap[LoopCosts[i].first] = i;
-      }
-    }
+    if (CC)
+      for (auto [Idx, Cost] : enumerate(CC->getLoopCosts()))
----------------
kasuga-fj wrote:

```suggestion
      for (const auto &[Idx, Cost] : enumerate(CC->getLoopCosts()))
```

https://github.com/llvm/llvm-project/pull/146105