Don't dynamically initialize dllimport vars (PR19933)

[hans]

Summary

It's wrong and it causes us to assert in LLVM's code emission.

[rnk]

lgtm

We should fix the LLVM assertion before committing this, though.

[hans]

Thanks! I've uploaded a patch for LLVM here: http://reviews.llvm.org/D4022

[hans]

Closed by commit rL210217 (authored by @hans).

cfe/trunk/lib/Sema/SemaTemplateInstantiateDecl.cpp

 void Sema::InstantiateVariableInitializer(
     VarDecl *Var, VarDecl *OldVar,
     const MultiLevelTemplateArgumentList &TemplateArgs) {
 
   if (Var->getAnyInitializer())
     // We already have an initializer in the class.
     return;
 
+  if (Var->hasAttr<DLLImportAttr>() &&
+      !(OldVar->getInit() && OldVar->checkInitIsICE())) {
+    // Do not dynamically initialize dllimport variables.
+    return;
+  }
+
   if (OldVar->getInit()) {
     if (Var->isStaticDataMember() && !OldVar->isOutOfLine())
       PushExpressionEvaluationContext(Sema::ConstantEvaluated, OldVar);
     else
       PushExpressionEvaluationContext(Sema::PotentiallyEvaluated, OldVar);
 
     // Instantiate the initializer.
     ExprResult Init =

cfe/trunk/test/CodeGenCXX/dllimport.cpp

 // RUN: %clang_cc1 -triple i686-windows-msvc   -fno-rtti -emit-llvm -std=c++1y -O0 -o - %s -DMSABI | FileCheck --check-prefix=MSC --check-prefix=M32 %s
 // RUN: %clang_cc1 -triple x86_64-windows-msvc -fno-rtti -emit-llvm -std=c++1y -O0 -o - %s -DMSABI | FileCheck --check-prefix=MSC --check-prefix=M64 %s
 // RUN: %clang_cc1 -triple i686-windows-gnu    -fno-rtti -emit-llvm -std=c++1y -O0 -o - %s         | FileCheck --check-prefix=GNU --check-prefix=G32 %s
 // RUN: %clang_cc1 -triple x86_64-windows-gnu  -fno-rtti -emit-llvm -std=c++1y -O0 -o - %s         | FileCheck --check-prefix=GNU --check-prefix=G64 %s
 // RUN: %clang_cc1 -triple i686-windows-msvc   -fno-rtti -emit-llvm -std=c++1y -O1 -o - %s -DMSABI | FileCheck --check-prefix=MO1 %s
 // RUN: %clang_cc1 -triple i686-windows-gnu    -fno-rtti -emit-llvm -std=c++1y -O1 -o - %s         | FileCheck --check-prefix=GO1 %s
 
+// CHECK-NOT doesn't play nice with CHECK-DAG, so use separate run lines.
+// RUN: %clang_cc1 -triple i686-windows-msvc   -fno-rtti -emit-llvm -std=c++1y -O0 -o - %s -DMSABI | FileCheck --check-prefix=MSC2 %s
+// RUN: %clang_cc1 -triple i686-windows-gnu    -fno-rtti -emit-llvm -std=c++1y -O0 -o - %s         | FileCheck --check-prefix=GNU2 %s
+
 // Helper structs to make templates more expressive.
 struct ImplicitInst_Imported {};
 struct ImplicitInst_NotImported {};
 struct ExplicitDecl_Imported {};
 struct ExplicitInst_Imported {};
 struct ExplicitSpec_Imported {};
 struct ExplicitSpec_Def_Imported {};
 struct ExplicitSpec_InlineDef_Imported {};

 USE(inlineDef)
 
 // inline attributes
 // MSC-DAG: declare dllimport void @"\01?noinline@@YAXXZ"()
 // GNU-DAG: declare dllimport void @_Z8noinlinev()
 __declspec(dllimport) __attribute__((noinline)) inline void noinline() {}
 USE(noinline)
 
+// MSC2-NOT: @"\01?alwaysInline@@YAXXZ"()
+// GNU2-NOT: @_Z12alwaysInlinev()
+__declspec(dllimport) __attribute__((always_inline)) inline void alwaysInline() {}
+USE(alwaysInline)
+
 // Redeclarations
 // MSC-DAG: declare dllimport void @"\01?redecl1@@YAXXZ"()
 // GNU-DAG: declare dllimport void @_Z7redecl1v()
 __declspec(dllimport) void redecl1();
 __declspec(dllimport) void redecl1();
 USE(redecl1)
 
 // NB: MSC issues a warning and makes redecl2/redecl3 dllexport. We follow GCC
namespace ClassTemplateStaticDef {
   template <typename T> struct __declspec(dllimport) S {
     static int x;
   };
   template <typename T> int S<T>::x;
   // CHECK-DAG: @"\01?x@?$S@H@ClassTemplateStaticDef@@2HA" = available_externally dllimport global i32 0
   int f() { return S<int>::x; }
 }
 
-//===----------------------------------------------------------------------===//
-// Negative checks
-//===----------------------------------------------------------------------===//
-
-// These checks are at the end to avoid interference with the DAG checks.
-
-// MSC-NOT: @"\01?alwaysInline@@YAXXZ"()
-// GNU-NOT: @_Z12alwaysInlinev()
-__declspec(dllimport) __attribute__((always_inline)) inline void alwaysInline() {}
-USE(alwaysInline)
+namespace PR19933 {
+// Don't dynamically initialize dllimport vars.
+// MSC2-NOT: @llvm.global_ctors
+// GNU2-NOT: @llvm.global_ctors
+
+  struct NonPOD { NonPOD(); };
+  template <typename T> struct A { static NonPOD x; };
+  template <typename T> NonPOD A<T>::x;
+  template struct __declspec(dllimport) A<int>;
+  // MSC-DAG: @"\01?x@?$A@H@PR19933@@2UNonPOD@2@A" = available_externally dllimport global %"struct.PR19933::NonPOD" zeroinitializer
+
+  int f();
+  template <typename T> struct B { static int x; };
+  template <typename T> int B<T>::x = f();
+  template struct __declspec(dllimport) B<int>;
+  // MSC-DAG: @"\01?x@?$B@H@PR19933@@2HA" = available_externally dllimport global i32 0
+
+  constexpr int g() { return 42; }
+  template <typename T> struct C { static int x; };
+  template <typename T> int C<T>::x = g();
+  template struct __declspec(dllimport) C<int>;
+  // MSC-DAG: @"\01?x@?$C@H@PR19933@@2HA" = available_externally dllimport global i32 42
+}