[clang] Suggest lifetime annotations [Issue Id: 169375] (PR #169767)

[Utkarsh Saxena via cfe-commits]

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@@ -31,7 +31,7 @@ inline llvm::raw_ostream &operator<<(llvm::raw_ostream &OS, LoanID ID) {
 struct AccessPath {
   const clang::ValueDecl *D;
 
-  AccessPath(const clang::ValueDecl *D) : D(D) {}
+  AccessPath(const clang::ValueDecl *D = nullptr) : D(D) {}
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usx95 wrote:

> If the root of the access path is a `ParmVarDecl,` we know it was a placeholder loan

This is different from borrowing the `ParmVarDecl`​ itself. A place holder loan is a loan held by the origin of ParmVarDecl and not a loan to the decl.  
Example in `int* foo(int* p) { int**x = &p; }`​, `&p`​ has a loan to `p`​ but `p`​ itself would contain the placeholder loan. Another thing is that these placeholder loans never expire(unlike other loans which expire when there access path gets destructed)

https://github.com/llvm/llvm-project/pull/169767