Allow TLS vars in dllimport/export functions; only inline dllimport functions when safe (PR24593)

This patch does two things:

1) Don't error about dllimport/export on thread-local static local variables.
   We put those attributes on static locals in dllimport/export functions
   implicitly in case the function gets inlined. Now, for TLS variables this
   is a problem because we can't import such variables, but it's a benign
   problem becase:

2) Make sure we never inline a dllimport function TLS static locals. In fact,
   never inline a dllimport function that references a non-imported function
   or variable (because these are not defined in the importing library). This
   seems to match MSVC's behaviour.

Differential Revision: http://reviews.llvm.org/D12422

llvm-svn: 246338

1 files changed, 11 insertions, 3 deletions

diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index c94d2dd5a9e..1fe6a5c18f1 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -9967,9 +9967,17 @@ Sema::FinalizeDeclaration(Decl *ThisDecl) {
   // dllimport/dllexport variables cannot be thread local, their TLS index
   // isn't exported with the variable.
   if (DLLAttr && VD->getTLSKind()) {
-    Diag(VD->getLocation(), diag::err_attribute_dll_thread_local) << VD
-                                                                  << DLLAttr;
-    VD->setInvalidDecl();
+    FunctionDecl *F = dyn_cast<FunctionDecl>(VD->getDeclContext());
+    if (F && getDLLAttr(F)) {
+      assert(VD->isStaticLocal());
+      // But if this is a static local in a dlimport/dllexport function, the
+      // function will never be inlined, which means the var would never be
+      // imported, so having it marked import/export is safe.
+    } else {
+      Diag(VD->getLocation(), diag::err_attribute_dll_thread_local) << VD
+                                                                    << DLLAttr;
+      VD->setInvalidDecl();
+    }
   }
 
   if (UsedAttr *Attr = VD->getAttr<UsedAttr>()) {