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

[Alina Sbirlea via llvm-commits]

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@@ -297,7 +297,8 @@ class CongruenceClass {
   using MemoryMemberSet = SmallPtrSet<const MemoryMemberType *, 2>;
 
   explicit CongruenceClass(unsigned ID) : ID(ID) {}
-  CongruenceClass(unsigned ID, Value *Leader, const Expression *E)
+  CongruenceClass(unsigned ID, std::pair<Value *, unsigned int> Leader,
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alinas wrote:

Add a comment describing what the items in the pair represent, specifically what is the int?

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