[clang] [LifetimeSafety] Implement multi-level origins (PR #168344)

[Gábor Horváth via cfe-commits]

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@@ -28,21 +29,30 @@ inline llvm::raw_ostream &operator<<(llvm::raw_ostream &OS, OriginID ID) {
 
 /// An Origin is a symbolic identifier that represents the set of possible
 /// loans a pointer-like object could hold at any given time.
-/// TODO: Enhance the origin model to handle complex types, pointer
-/// indirection and reborrowing. The plan is to move from a single origin per
-/// variable/expression to a "list of origins" governed by the Type.
-/// For example, the type 'int**' would have two origins.
-/// See discussion:
-/// https://github.com/llvm/llvm-project/pull/142313/commits/0cd187b01e61b200d92ca0b640789c1586075142#r2137644238
+///
+/// Each Origin corresponds to a single level of indirection. For complex types
+/// with multiple levels of indirection (e.g., `int**`), multiple Origins are
+/// organized into an OriginTree structure (see below).
 struct Origin {
   OriginID ID;
   /// A pointer to the AST node that this origin represents. This union
   /// distinguishes between origins from declarations (variables or parameters)
   /// and origins from expressions.
   llvm::PointerUnion<const clang::ValueDecl *, const clang::Expr *> Ptr;
 
-  Origin(OriginID ID, const clang::ValueDecl *D) : ID(ID), Ptr(D) {}
-  Origin(OriginID ID, const clang::Expr *E) : ID(ID), Ptr(E) {}
+  /// The type at this indirection level.
+  ///
+  /// For `int** pp`:
+  ///   Root origin: QT = `int**` (what pp points to)
+  ///   Pointee origin: QT = `int*` (what *pp points to)
+  ///
+  /// Null for synthetic lvalue origins (e.g., outer origin of DeclRefExpr).
+  QualType QT;
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Xazax-hun wrote:

Is the qualifier important for the loans? If not, I wonder if having a `const Type*` directly would be better. 

https://github.com/llvm/llvm-project/pull/168344