[llvm] [DominanceFrontier] make iterating dereferenced DominanceFrontierBase::find deterministic (PR #69711)

[Wenju He via llvm-commits]

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@@ -39,7 +39,9 @@ class raw_ostream;
 template <class BlockT, bool IsPostDom>
 class DominanceFrontierBase {
 public:
-  using DomSetType = std::set<BlockT *>;                // Dom set for a bb
+  // Dom set for a bb. Use SetVector to make iterating dom frontiers of a bb
+  // deterministic.
+  using DomSetType = SetVector<BlockT *>;
   using DomSetMapType = std::map<BlockT *, DomSetType>; // Dom set map
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wenju-he wrote:

https://llvm.org/docs/CodingStandards.html says `llvm::DenseMap should almost always be used instead of std::map`, shall I change it to DenseMap?

https://github.com/llvm/llvm-project/pull/69711