Drop 'dllimport' when redeclaring inline function template without the attribute (PR31695)

For non-template dllimport functions, MSVC allows providing an inline
definition without spelling out the attribute again. In the example below, f
remains a dllimport function.

  __declspec(dllimport) int f();
  inline int f() { return 42; }

  int useit() {
    return f();
  }

However, for a function template, not putting dllimport on the redeclaration
causes it to be dropped. In the example below, f is not dllimport.

  template <typename> __declspec(dllimport) int f();
  template <typename> inline int f() { return 42; }

  int useit() {
    return f<int>();
  }

This patch makes Clang match MSVC for the second example.

MSVC does not warn about the attribute being dropped in the example above, but
I think we should. (MSVC does warn if the inline keyword isn't used.)

Differential Revision: https://reviews.llvm.org/D29152

llvm-svn: 293800

1 files changed, 11 insertions, 5 deletions

diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index 60daae056b3..32663121f88 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -5702,13 +5702,17 @@ static void checkDLLAttributeRedeclaration(Sema &S, NamedDecl *OldDecl,
   if (OldDecl->isInvalidDecl())
     return;
 
+  bool IsTemplate = false;
   if (TemplateDecl *OldTD = dyn_cast<TemplateDecl>(OldDecl)) {
     OldDecl = OldTD->getTemplatedDecl();
+    IsTemplate = true;
     if (!IsSpecialization)
       IsDefinition = false;
   }
-  if (TemplateDecl *NewTD = dyn_cast<TemplateDecl>(NewDecl))
+  if (TemplateDecl *NewTD = dyn_cast<TemplateDecl>(NewDecl)) {
     NewDecl = NewTD->getTemplatedDecl();
+    IsTemplate = true;
+  }
 
   if (!OldDecl || !NewDecl)
     return;
@@ -5761,9 +5765,10 @@ static void checkDLLAttributeRedeclaration(Sema &S, NamedDecl *OldDecl,
   }
 
   // A redeclaration is not allowed to drop a dllimport attribute, the only
-  // exceptions being inline function definitions, local extern declarations,
-  // qualified friend declarations or special MSVC extension: in the last case,
-  // the declaration is treated as if it were marked dllexport.
+  // exceptions being inline function definitions (except for function
+  // templates), local extern declarations, qualified friend declarations or
+  // special MSVC extension: in the last case, the declaration is treated as if
+  // it were marked dllexport.
   bool IsInline = false, IsStaticDataMember = false, IsQualifiedFriend = false;
   bool IsMicrosoft = S.Context.getTargetInfo().getCXXABI().isMicrosoft();
   if (const auto *VD = dyn_cast<VarDecl>(NewDecl)) {
@@ -5778,7 +5783,8 @@ static void checkDLLAttributeRedeclaration(Sema &S, NamedDecl *OldDecl,
                         FD->getFriendObjectKind() == Decl::FOK_Declared;
   }
 
-  if (OldImportAttr && !HasNewAttr && !IsInline && !IsStaticDataMember &&
+  if (OldImportAttr && !HasNewAttr &&
+      (!IsInline || (IsMicrosoft && IsTemplate)) && !IsStaticDataMember &&
       !NewDecl->isLocalExternDecl() && !IsQualifiedFriend) {
     if (IsMicrosoft && IsDefinition) {
       S.Diag(NewDecl->getLocation(),