[MinGW] Reject explicit non-default visibility applied to dllexport/dllimport declaration

dllimport/dllexport is incompatible with protected/hidden visibilities.
(Arguably dllexport semantics is compatible with protected but let's reject the
combo for simplicity.)

When an explicit visibility attribute applies on a dllexport/dllimport
declaration, report a Frontend error (Sema does not compute visibility).

Reviewed By: mstorsjo

Differential Revision: https://reviews.llvm.org/D133266

1 files changed, 8 insertions, 2 deletions

diff --git a/clang/lib/CodeGen/CodeGenModule.cpp b/clang/lib/CodeGen/CodeGenModule.cpp
index f9087cdd5d4d..64a9e9d6f4c4 100644
--- a/clang/lib/CodeGen/CodeGenModule.cpp
+++ b/clang/lib/CodeGen/CodeGenModule.cpp
@@ -1099,8 +1099,6 @@ llvm::ConstantInt *CodeGenModule::getSize(CharUnits size) {
 
 void CodeGenModule::setGlobalVisibility(llvm::GlobalValue *GV,
                                         const NamedDecl *D) const {
-  if (GV->hasDLLExportStorageClass() || GV->hasDLLImportStorageClass())
-    return;
   // Internal definitions always have default visibility.
   if (GV->hasLocalLinkage()) {
     GV->setVisibility(llvm::GlobalValue::DefaultVisibility);
@@ -1111,6 +1109,14 @@ void CodeGenModule::setGlobalVisibility(llvm::GlobalValue *GV,
   // Set visibility for definitions, and for declarations if requested globally
   // or set explicitly.
   LinkageInfo LV = D->getLinkageAndVisibility();
+  if (GV->hasDLLExportStorageClass() || GV->hasDLLImportStorageClass()) {
+    // Reject explicit non-default visibility on dllexport/dllimport.
+    if (LV.isVisibilityExplicit() && LV.getVisibility() != DefaultVisibility)
+      getDiags().Report(D->getLocation(),
+                        diag::err_non_default_visibility_dllstorage)
+          << (GV->hasDLLExportStorageClass() ? "dllexport" : "dllimport");
+    return;
+  }
   if (LV.isVisibilityExplicit() || getLangOpts().SetVisibilityForExternDecls ||
       !GV->isDeclarationForLinker())
     GV->setVisibility(GetLLVMVisibility(LV.getVisibility()));