[llvm] [PGO][NFC] Make CFGMST debug dump order deterministic (PR #200835)

[Yaxun Liu via llvm-commits]

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@@ -286,12 +286,30 @@ template <class Edge, class BBInfo> class CFGMST {
     if (!Message.str().empty())
       OS << Message << "\n";
     OS << "  Number of Basic Blocks: " << BBInfos.size() << "\n";
-    for (auto &BI : BBInfos) {
-      const BasicBlock *BB = BI.first;
+    // Collect and sort BBInfos deterministically by their assigned Index.
+    std::vector<std::pair<const BasicBlock *, const BBInfo *>> SortedBBInfos;
+    SortedBBInfos.reserve(BBInfos.size());
+    for (const auto &BI : BBInfos)
+      SortedBBInfos.emplace_back(BI.first, BI.second.get());
+
+    llvm::sort(SortedBBInfos, [](const auto &A, const auto &B) {
+      // Primary key: BBInfo Index
+      if (A.second->Index != B.second->Index)
+        return A.second->Index < B.second->Index;
+      // Secondary key: name string to keep a stable order even if
+      // indices tie (ties shouldn't happen, but this makes ordering
+      // explicit).
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yxsamliu wrote:

Added a debug-only assert to check that BBInfo indices are unique before sorting. Release builds have no extra cost, and the name tiebreaker is still kept for deterministic dump output.

https://github.com/llvm/llvm-project/pull/200835