[dllexport] Instantiate default ctor default args

[peterjc123]

Summary

Fixes https://bugs.llvm.org/show_bug.cgi?id=51414.

[rnk]

I think it looks good, but it needs a test.

I worry that we might have the same bug for copy closures, but the fix will be different, since those are used in exception handling.

[peterjc123]

In D108021#2943842, @rnk wrote:

I think it looks good, but it needs a test.

I worry that we might have the same bug for copy closures, but the fix will be different, since those are used in exception handling.

Thanks for your review. Since I'm pretty new to this repo, could you please tell me how to write a test here?

[peterjc123]

Add test

[peterjc123]

Add test

[peterjc123]

Add test

[peterjc123]

@rnk @hans Test added. Please take some time to review the changes.

[peterjc123]

Skip in template classes

[peterjc123]

clang-format

[peterjc123]

clang-tidy

[rnk]

Thanks for the patch and test. Can I commit this for you?

clang/lib/Sema/SemaDeclCXX.cpp

6012

This should probably happen when explicit instantiation definitions are exported, so the TSK_ExplicitInstantiationDefinition case. However, I don't consider it a blocking issue.

[peterjc123]

Sure, please do that.

clang/lib/Sema/SemaDeclCXX.cpp

6012

Well, I cannot constuct one code example that includes explicit instantiation definitions which triggers this problem. If you could provide one, then I may look into it.

clang/lib/Sema/SemaDeclCXX.cpp

       if (TSK == TSK_ImplicitInstantiation && !ClassAttr->isInherited())
         continue;
 
+      // If this is an MS ABI dllexport default constructor, instantiate any
+      // default arguments.
+      if (S.Context.getTargetInfo().getCXXABI().isMicrosoft()) {
+        auto CD = dyn_cast<CXXConstructorDecl>(MD);
+        if (CD && CD->isDefaultConstructor()) {
+          S.InstantiateDefaultCtorDefaultArgs(CD);
+        }
+      }
+
       S.MarkFunctionReferenced(Class->getLocation(), MD);
 
       // The function will be passed to the consumer when its definition is

clang/test/CodeGenCXX/dllexport-ctor-closure-nested.cpp

+// RUN: %clang_cc1 -triple i686-windows-msvc -emit-llvm -std=c++14 \
+// RUN:    -fno-threadsafe-statics -fms-extensions -O1 -mconstructor-aliases \
+// RUN:    -disable-llvm-passes -o - %s -w -fms-compatibility-version=19.00 | \
+// RUN:    FileCheck %s
+
+struct HasDtor {
+  ~HasDtor();
+  int o;
+};
+struct HasImplicitDtor1 { HasDtor o; };
+struct __declspec(dllexport) CtorClosureOuter {
+  struct __declspec(dllexport) CtorClosureInner {
+    CtorClosureInner(const HasImplicitDtor1 &v = {}) {}
+  };
+};
+
+// CHECK-LABEL: define weak_odr dso_local dllexport x86_thiscallcc void @"??_FCtorClosureInner@CtorClosureOuter@@QAEXXZ"({{.*}}) {{#[0-9]+}} comdat
+// CHECK-LABEL: $"??1HasImplicitDtor1@@QAE@XZ" = comdat any