[clang] [Clang] Instantiate constexpr function when they are needed. (PR #173537)

[Erich Keane via cfe-commits]

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@@ -161,6 +162,10 @@ void clang::ParseAST(Sema &S, bool PrintStats, bool SkipFunctionBodies) {
       return M;
     });
     P.Initialize();
+
+    llvm::scope_exit _([&S]() { S.unregisterSemaProxy(); });
+    S.registerSemaProxy();
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erichkeane wrote:

Do we want to unregister BEFORE the `Consumer->HandleTopLevelDecls`?  We probably don't need this during codegen, do we?

https://github.com/llvm/llvm-project/pull/173537