commit dd96db2c034ce7700f4a4943bf148834adca42e7
author Hans Wennborg <hans@hanshq.net> Wed Aug 27 21:27:40 2014 +0000
committer Hans Wennborg <hans@hanshq.net> Wed Aug 27 21:27:40 2014 +0000
tree ecfb5452ff7b8e9fffbd17d98272639defc55876
parent cdb871d734232e38a5b17e12bdf4d713d6850998

Allow adding dll attributes on certain redecls with a warning if the decl hasn't been used yet (PR20746)

This shouldn't really be allowed, but it comes up in real code (see PR). As
long as the decl hasn't been used there's no technical difficulty in supporting
it, so downgrade the error to a warning.

Differential Revision: http://reviews.llvm.org/D5087

llvm-svn: 216619

clang/lib/Sema/SemaDecl.cpp

diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index e5cf31a..2d2f973 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -5075,7 +5075,7 @@
     NewDecl = NewTD->getTemplatedDecl();
 
   if (!OldDecl || !NewDecl)
-      return;
+    return;
 
   const DLLImportAttr *OldImportAttr = OldDecl->getAttr<DLLImportAttr>();
   const DLLExportAttr *OldExportAttr = OldDecl->getAttr<DLLExportAttr>();
@@ -5092,13 +5092,30 @@
   // Implicitly generated declarations are also excluded for now because there
   // is no other way to switch these to use dllimport or dllexport.
   bool AddsAttr = !(OldImportAttr || OldExportAttr) && HasNewAttr;
+
   if (AddsAttr && !IsSpecialization && !OldDecl->isImplicit()) {
-    S.Diag(NewDecl->getLocation(), diag::err_attribute_dll_redeclaration)
-      << NewDecl
-      << (NewImportAttr ? (const Attr *)NewImportAttr : NewExportAttr);
+    // If the declaration hasn't been used yet, allow with a warning for
+    // free functions and global variables.
+    bool JustWarn = false;
+    if (!OldDecl->isUsed() && OldDecl->getDeclContext()->isFileContext()) {
+      auto *VD = dyn_cast<VarDecl>(OldDecl);
+      if (VD && !VD->getDescribedVarTemplate())
+        JustWarn = true;
+      auto *FD = dyn_cast<FunctionDecl>(OldDecl);
+      if (FD && FD->getTemplatedKind() == FunctionDecl::TK_NonTemplate)
+        JustWarn = true;
+    }
+
+    unsigned DiagID = JustWarn ? diag::warn_attribute_dll_redeclaration
+                               : diag::err_attribute_dll_redeclaration;
+    S.Diag(NewDecl->getLocation(), DiagID)
+        << NewDecl
+        << (NewImportAttr ? (const Attr *)NewImportAttr : NewExportAttr);
     S.Diag(OldDecl->getLocation(), diag::note_previous_declaration);
-    NewDecl->setInvalidDecl();
-    return;
+    if (!JustWarn) {
+      NewDecl->setInvalidDecl();
+      return;
+    }
   }
 
   // A redeclaration is not allowed to drop a dllimport attribute, the only