[llvm] [GVN] Refactor the LeaderTable structure into a properly encapsulated data structure (PR #88347)

[Nikita Popov via llvm-commits]

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@@ -232,13 +232,67 @@ class GVNPass : public PassInfoMixin<GVNPass> {
 
   /// A mapping from value numbers to lists of Value*'s that
   /// have that value number.  Use findLeader to query it.
-  struct LeaderTableEntry {
-    Value *Val;
-    const BasicBlock *BB;
-    LeaderTableEntry *Next;
+  class LeaderMap {
+  public:
+    struct LeaderTableEntry {
+      Value *Val;
+      const BasicBlock *BB;
+    };
+
+  private:
+    struct LeaderListNode {
+      LeaderTableEntry Entry;
+      LeaderListNode *Next;
+    };
+    DenseMap<uint32_t, LeaderListNode> NumToLeaders;
+    BumpPtrAllocator TableAllocator;
+
+  public:
+    class leader_iterator {
+      const LeaderListNode *Current;
+
+    public:
+      using iterator_category = std::forward_iterator_tag;
+      using value_type = const LeaderTableEntry;
+      using difference_type = std::ptrdiff_t;
+      using pointer = value_type *;
+      using reference = value_type &;
+
+      leader_iterator(const LeaderListNode *C) : Current(C) {}
+      leader_iterator &operator++() {
+        assert(Current && "Dereferenced end of leader list!");
+        Current = Current->Next;
+        return *this;
+      }
+      bool operator==(const leader_iterator &other) const {
----------------
nikic wrote:

```suggestion
      bool operator==(const leader_iterator &Other) const {
```

https://github.com/llvm/llvm-project/pull/88347