[clang] [C++20] [Modules] Instantiate pending instantiations when GMF ends (PR #126842)

[Matheus Izvekov via cfe-commits]

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@@ -1104,9 +1104,13 @@ void Sema::ActOnStartOfTranslationUnit() {
 }
 
 void Sema::ActOnEndOfTranslationUnitFragment(TUFragmentKind Kind) {
-  // No explicit actions are required at the end of the global module fragment.
-  if (Kind == TUFragmentKind::Global)
+  if (Kind == TUFragmentKind::Global) {
+    // Perform Pending Instantiations at the end of global module fragment so
+    // that the module ownership of TU-level decls won't get messed.
+    llvm::TimeTraceScope TimeScope("PerformPendingInstantiations");
+    PerformPendingInstantiations();
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mizvekov wrote:

I didn't state my point clearly enough, sorry about that.

What I mean is, we can for example always set instantiation ownership to the same as the pattern, and that is just
as consistent and correct, but should be a simpler change and have higher performance, as we will still batch up pending instantiations the same as before, correct?

https://github.com/llvm/llvm-project/pull/126842