[clang] Reduce memory usage in AST parent map generation by lazily checking if nodes have been seen (PR #129934)

[via cfe-commits]

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@@ -69,17 +70,22 @@ class ParentMapContext::ParentMap {
       for (; N > 0; --N)
         push_back(Value);
     }
-    bool contains(const DynTypedNode &Value) {
-      return Seen.contains(Value);
+    bool contains(const DynTypedNode &Value) const {
+      const void *Identity = Value.getMemoizationData();
+      assert(Identity);
+      return Dedup.contains(Identity);
     }
     void push_back(const DynTypedNode &Value) {
-      if (!Value.getMemoizationData() || Seen.insert(Value).second)
+      const void *Identity = Value.getMemoizationData();
+      if (!Identity || Dedup.insert(Identity).second) {
         Items.push_back(Value);
+      }
     }
     llvm::ArrayRef<DynTypedNode> view() const { return Items; }
+
   private:
-    llvm::SmallVector<DynTypedNode, 2> Items;
-    llvm::SmallDenseSet<DynTypedNode, 2> Seen;
+    std::vector<DynTypedNode> Items;
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cor3ntin wrote:

I think it would be better (std::vector _always_ allocate)

https://github.com/llvm/llvm-project/pull/129934