[clang] [LifetimeSafety] Implement dataflow analysis for loan propagation (PR #148065)

[Yitzhak Mandelbaum via cfe-commits]

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@@ -493,7 +496,241 @@ class FactGenerator : public ConstStmtVisitor<FactGenerator> {
 };
 
 // ========================================================================= //
-//  TODO: Run dataflow analysis to propagate loans, analyse and error reporting.
+//                              The Dataflow Lattice
+// ========================================================================= //
+
+// Using LLVM's immutable collections is efficient for dataflow analysis
+// as it avoids deep copies during state transitions.
+// TODO(opt): Consider using a bitset to represent the set of loans.
+using LoanSet = llvm::ImmutableSet<LoanID>;
+using OriginLoanMap = llvm::ImmutableMap<OriginID, LoanSet>;
+
+/// An object to hold the factories for immutable collections, ensuring
+/// that all created states share the same underlying memory management.
+struct LifetimeFactory {
+  OriginLoanMap::Factory OriginMapFact;
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ymand wrote:

+1

https://github.com/llvm/llvm-project/pull/148065