[llvm] [NewGVN] Prevent cyclic dependencies by ensuring Leader has min RPO number (PR #82110)

[Alina Sbirlea via llvm-commits]

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@@ -311,15 +312,21 @@ class CongruenceClass {
   }
 
   // Leader functions
-  Value *getLeader() const { return RepLeader; }
-  void setLeader(Value *Leader) { RepLeader = Leader; }
+  Value *getLeader() const { return RepLeader.first; }
+  void setLeader(std::pair<Value *, unsigned int> Leader) {
+    RepLeader = Leader;
+  }
   const std::pair<Value *, unsigned int> &getNextLeader() const {
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alinas wrote:

This can be a separate NFC: I see no use for having getNextLeader return the pair, could return the .first like getLeader().

https://github.com/llvm/llvm-project/pull/82110