[PATCH] Implement __declspec(selectany) under -fms-extensions

[Rafael Espíndola]

Can they be discarded? If so, please add a comment saying that they
can. If not, you need no use weak_odr.

On 17 May 2013 13:22, Reid Kleckner <rnk at google.com> wrote:
> selectany only applies to externally visible global variables.  It has
> the effect of making the data linkonce.  MSDN doesn't seem to require
> that all definitions be the same, which means clang shouldn't use
> linkonceodr.
>
> http://llvm-reviews.chandlerc.com/D814
>
> Files:
>   include/clang/Basic/Attr.td
>   include/clang/Basic/DiagnosticSemaKinds.td
>   lib/CodeGen/CodeGenModule.cpp
>   lib/Sema/SemaDecl.cpp
>   lib/Sema/SemaDeclAttr.cpp
>   test/CodeGen/ms-declspecs.c
>   test/SemaCXX/attr-selectany.cpp
>
> Index: include/clang/Basic/Attr.td
> ===================================================================
> --- include/clang/Basic/Attr.td
> +++ include/clang/Basic/Attr.td
> @@ -948,6 +948,10 @@
>    let Spellings = [Keyword<"__forceinline">];
>  }
>
> +def SelectAny : InheritableAttr {
> +  let Spellings = [Declspec<"selectany">];
> +}
> +
>  def Win64 : InheritableAttr {
>    let Spellings = [Keyword<"__w64">];
>  }
> Index: include/clang/Basic/DiagnosticSemaKinds.td
> ===================================================================
> --- include/clang/Basic/DiagnosticSemaKinds.td
> +++ include/clang/Basic/DiagnosticSemaKinds.td
> @@ -1950,6 +1950,8 @@
>    "weak identifier %0 never declared">;
>  def err_attribute_weak_static : Error<
>    "weak declaration cannot have internal linkage">;
> +def err_attribute_selectany_non_extern_data : Error<
> +  "'selectany' can only be applied to data items with external linkage">;
>  def warn_attribute_weak_import_invalid_on_definition : Warning<
>    "'weak_import' attribute cannot be specified on a definition">,
>    InGroup<IgnoredAttributes>;
> Index: lib/CodeGen/CodeGenModule.cpp
> ===================================================================
> --- lib/CodeGen/CodeGenModule.cpp
> +++ lib/CodeGen/CodeGenModule.cpp
> @@ -1937,7 +1937,12 @@
>      return llvm::Function::DLLImportLinkage;
>    else if (D->hasAttr<DLLExportAttr>())
>      return llvm::Function::DLLExportLinkage;
> -  else if (D->hasAttr<WeakAttr>()) {
> +  else if (D->hasAttr<SelectAnyAttr>()) {
> +    // MSDN does not say that selectany globals all have to have the same
> +    // definition, so we use linkonce instead of linkonceodr here to be
> +    // conservative.
> +    return llvm::GlobalVariable::LinkOnceAnyLinkage;
> +  } else if (D->hasAttr<WeakAttr>()) {
>      if (GV->isConstant())
>        return llvm::GlobalVariable::WeakODRLinkage;
>      else
> Index: lib/Sema/SemaDecl.cpp
> ===================================================================
> --- lib/Sema/SemaDecl.cpp
> +++ lib/Sema/SemaDecl.cpp
> @@ -4636,6 +4636,15 @@
>        ND.dropAttr<WeakRefAttr>();
>      }
>    }
> +
> +  // 'selectany' only applies to externally visible varable declarations.
> +  // It does not apply to functions.
> +  if (SelectAnyAttr *Attr = ND.getAttr<SelectAnyAttr>()) {
> +    if (isa<FunctionDecl>(ND) || !ND.isExternallyVisible()) {
> +      S.Diag(Attr->getLocation(), diag::err_attribute_selectany_non_extern_data);
> +      ND.dropAttr<SelectAnyAttr>();
> +    }
> +  }
>  }
>
>  /// Given that we are within the definition of the given function,
> Index: lib/Sema/SemaDeclAttr.cpp
> ===================================================================
> --- lib/Sema/SemaDeclAttr.cpp
> +++ lib/Sema/SemaDeclAttr.cpp
> @@ -4690,6 +4690,16 @@
>                               Attr.getAttributeSpellingListIndex()));
>  }
>
> +static void handleSelectAnyAttr(Sema &S, Decl *D, const AttributeList &Attr) {
> +  if (!checkMicrosoftExt(S, Attr))
> +    return;
> +  // Check linkage after possibly merging declaratinos.  See
> +  // checkAttributesAfterMerging().
> +  D->addAttr(::new (S.Context)
> +             SelectAnyAttr(Attr.getRange(), S.Context,
> +                           Attr.getAttributeSpellingListIndex()));
> +}
> +
>  //===----------------------------------------------------------------------===//
>  // Top Level Sema Entry Points
>  //===----------------------------------------------------------------------===//
> @@ -4916,6 +4926,9 @@
>    case AttributeList::AT_ForceInline:
>      handleForceInlineAttr(S, D, Attr);
>      break;
> +  case AttributeList::AT_SelectAny:
> +    handleSelectAnyAttr(S, D, Attr);
> +    break;
>
>    // Thread safety attributes:
>    case AttributeList::AT_GuardedVar:
> Index: test/CodeGen/ms-declspecs.c
> ===================================================================
> --- test/CodeGen/ms-declspecs.c
> +++ test/CodeGen/ms-declspecs.c
> @@ -1,5 +1,10 @@
>  // RUN: %clang_cc1 -triple i386-pc-win32 %s -emit-llvm -fms-compatibility -o - | FileCheck %s
>
> +__declspec(selectany) int x1 = 1;
> +const __declspec(selectany) int x2 = 2;
> +// CHECK: @x1 = linkonce global i32 1, align 4
> +// CHECK: @x2 = linkonce constant i32 2, align 4
> +
>  struct __declspec(align(16)) S {
>    char x;
>  };
> Index: test/SemaCXX/attr-selectany.cpp
> ===================================================================
> --- /dev/null
> +++ test/SemaCXX/attr-selectany.cpp
> @@ -0,0 +1,26 @@
> +// RUN: %clang_cc1 -fms-extensions -fsyntax-only -verify %s
> +// MSVC produces similar diagnostics.
> +
> +__declspec(selectany) void foo() { } // expected-error{{'selectany' can only be applied to data items with external linkage}}
> +
> +__declspec(selectany) int x1 = 1;
> +
> +const __declspec(selectany) int x2 = 2; // expected-error{{'selectany' can only be applied to data items with external linkage}}
> +
> +extern const __declspec(selectany) int x3 = 3;
> +
> +extern const int x4;
> +const __declspec(selectany) int x4 = 4;
> +
> +// MSDN says this is incorrect, but MSVC doesn't diagnose it.
> +extern __declspec(selectany) int x5;
> +
> +static __declspec(selectany) int x6 = 2; // expected-error{{'selectany' can only be applied to data items with external linkage}}
> +
> +class X {
> + public:
> +  X(int i) { i++; };
> +  int i;
> +};
> +
> +__declspec(selectany) X x(1);
>
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