[MS] Instantiate default args during instantiation of exported default ctors

Summary:
Replace some old code that probably pre-dated the change to delay
emission of dllexported code until after the closing brace of the
outermost record type. Only uninstantiated default argument expressions
need to be handled now. It is enough to instantiate default argument
expressions when instantiating dllexported default ctors. This also
fixes some double-diagnostic issues in this area.

Fixes PR31500

Reviewers: rsmith

Subscribers: cfe-commits

Differential Revision: https://reviews.llvm.org/D28274

llvm-svn: 291045

1 files changed, 31 insertions, 4 deletions

diff --git a/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp b/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
index 3cc938106d8..f4013b82064 100644
--- a/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
+++ b/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
@@ -3619,6 +3619,27 @@ TemplateDeclInstantiator::InitMethodInstantiation(CXXMethodDecl *New,
   return false;
 }
 
+/// In the MS ABI, we need to instantiate default arguments of dllexported
+/// default constructors along with the constructor definition. This allows IR
+/// gen to emit a constructor closure which calls the default constructor with
+/// its default arguments.
+static void InstantiateDefaultCtorDefaultArgs(Sema &S,
+                                              CXXConstructorDecl *Ctor) {
+  assert(S.Context.getTargetInfo().getCXXABI().isMicrosoft() &&
+         Ctor->isDefaultConstructor());
+  unsigned NumParams = Ctor->getNumParams();
+  if (NumParams == 0)
+    return;
+  DLLExportAttr *Attr = Ctor->getAttr<DLLExportAttr>();
+  if (!Attr)
+    return;
+  for (unsigned I = 0; I != NumParams; ++I) {
+    (void)S.CheckCXXDefaultArgExpr(Attr->getLocation(), Ctor,
+                                   Ctor->getParamDecl(I));
+    S.DiscardCleanupsInEvaluationContext();
+  }
+}
+
 /// \brief Instantiate the definition of the given function from its
 /// template.
 ///
@@ -3796,11 +3817,17 @@ void Sema::InstantiateFunctionDefinition(SourceLocation PointOfInstantiation,
                                          TemplateArgs))
       return;
 
-    // If this is a constructor, instantiate the member initializers.
-    if (const CXXConstructorDecl *Ctor =
-          dyn_cast<CXXConstructorDecl>(PatternDecl)) {
-      InstantiateMemInitializers(cast<CXXConstructorDecl>(Function), Ctor,
+    if (CXXConstructorDecl *Ctor = dyn_cast<CXXConstructorDecl>(Function)) {
+      // If this is a constructor, instantiate the member initializers.
+      InstantiateMemInitializers(Ctor, cast<CXXConstructorDecl>(PatternDecl),
                                  TemplateArgs);
+
+      // If this is an MS ABI dllexport default constructor, instantiate any
+      // default arguments.
+      if (Context.getTargetInfo().getCXXABI().isMicrosoft() &&
+          Ctor->isDefaultConstructor()) {
+        InstantiateDefaultCtorDefaultArgs(*this, Ctor);
+      }
     }
 
     // Instantiate the function body.