r242973 - Downgrade error about adding 'dllimport' to used free function to warning (PR24215)

[Hans Wennborg]

This isn't fixing a regression, but would be nice to have in 3.7 I think.

Richard, is this OK for merging?

On Wed, Jul 22, 2015 at 4:54 PM, Hans Wennborg <hans at hanshq.net> wrote:
> Author: hans
> Date: Wed Jul 22 18:54:51 2015
> New Revision: 242973
>
> URL: http://llvm.org/viewvc/llvm-project?rev=242973&view=rev
> Log:
> Downgrade error about adding 'dllimport' to used free function to warning (PR24215)
>
> The code will still work as it can reference the function via its thunk.
>
> Modified:
>     cfe/trunk/lib/Sema/SemaDecl.cpp
>     cfe/trunk/test/Sema/dllimport.c
>
> Modified: cfe/trunk/lib/Sema/SemaDecl.cpp
> URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Sema/SemaDecl.cpp?rev=242973&r1=242972&r2=242973&view=diff
> ==============================================================================
> --- cfe/trunk/lib/Sema/SemaDecl.cpp (original)
> +++ cfe/trunk/lib/Sema/SemaDecl.cpp Wed Jul 22 18:54:51 2015
> @@ -5368,10 +5368,9 @@ static void checkDLLAttributeRedeclarati
>    bool AddsAttr = !(OldImportAttr || OldExportAttr) && HasNewAttr;
>
>    if (AddsAttr && !IsSpecialization && !OldDecl->isImplicit()) {
> -    // If the declaration hasn't been used yet, allow with a warning for
> -    // free functions and global variables.
> +    // Allow with a warning for free functions and global variables.
>      bool JustWarn = false;
> -    if (!OldDecl->isUsed() && !OldDecl->isCXXClassMember()) {
> +    if (!OldDecl->isCXXClassMember()) {
>        auto *VD = dyn_cast<VarDecl>(OldDecl);
>        if (VD && !VD->getDescribedVarTemplate())
>          JustWarn = true;
> @@ -5380,6 +5379,13 @@ static void checkDLLAttributeRedeclarati
>          JustWarn = true;
>      }
>
> +    // We cannot change a declaration that's been used because IR has already
> +    // been emitted. Dllimported functions will still work though (modulo
> +    // address equality) as they can use the thunk.
> +    if (OldDecl->isUsed())
> +      if (!isa<FunctionDecl>(OldDecl) || !NewImportAttr)
> +        JustWarn = false;
> +
>      unsigned DiagID = JustWarn ? diag::warn_attribute_dll_redeclaration
>                                 : diag::err_attribute_dll_redeclaration;
>      S.Diag(NewDecl->getLocation(), DiagID)
>
> Modified: cfe/trunk/test/Sema/dllimport.c
> URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/Sema/dllimport.c?rev=242973&r1=242972&r2=242973&view=diff
> ==============================================================================
> --- cfe/trunk/test/Sema/dllimport.c (original)
> +++ cfe/trunk/test/Sema/dllimport.c Wed Jul 22 18:54:51 2015
> @@ -143,7 +143,7 @@ __declspec(dllimport) void redecl3(); //
>
>                        void redecl4(); // expected-note{{previous declaration is here}}
>  void useRedecl4() { redecl4(); }
> -__declspec(dllimport) void redecl4(); // expected-error{{redeclaration of 'redecl4' cannot add 'dllimport' attribute}}
> +__declspec(dllimport) void redecl4(); // expected-warning{{redeclaration of 'redecl4' should not add 'dllimport' attribute}}
>
>  // Allow with a warning if the decl hasn't been used yet.
>                        void redecl5(); // expected-note{{previous declaration is here}}
>
>
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