[llvm] [GenericDomTree] Use range-based for loops (NFC) (PR #96404)

[Nikita Popov via llvm-commits]

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@@ -882,9 +879,9 @@ class DominatorTreeBase {
     // changed.
     if (!NewBBIDom) return;
 
-    for (i = i + 1; i < PredBlocks.size(); ++i) {
-      if (isReachableFromEntry(PredBlocks[i]))
-        NewBBIDom = findNearestCommonDominator(NewBBIDom, PredBlocks[i]);
+    for (const auto &Pred : llvm::drop_begin(PredBlocks)) {
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nikic wrote:

That's not right -- this loop is supposed to pick up where the last one stopped, not skip just the first element.

The code is still correct because the NCD operation is idempotent, but it makes the code less efficient.

https://github.com/llvm/llvm-project/pull/96404