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

[Reid Kleckner]

    - Use weak instead of linkonce.

http://llvm-reviews.chandlerc.com/D814

CHANGE SINCE LAST DIFF
  http://llvm-reviews.chandlerc.com/D814?vs=2010&id=2011#toc

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 +1937,14 @@
     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 a non-ODR linkage.  It also implies that we cannot
+    // discared unused symbols until link time, so we use weak instead of
+    // linkonce.
+    // http://msdn.microsoft.com/en-us/library/5tkz6s71.aspx
+    return llvm::GlobalVariable::WeakAnyLinkage;
+  } 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 = weak global i32 1, align 4
+// CHECK: @x2 = weak 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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