[MinGW] Don't mark external variables as DSO local

Since MinGW supports automatically importing external variables from
DLLs even without the DLLImport attribute, we shouldn't mark them
as DSO local unless we actually know them to be local for sure.

Keep marking thread local variables as DSO local.

Differential Revision: https://reviews.llvm.org/D51382

llvm-svn: 340941

7 files changed, 44 insertions, 6 deletions

diff --git a/clang/lib/CodeGen/CodeGenModule.cpp b/clang/lib/CodeGen/CodeGenModule.cpp
index 29692eedb53..c5cac6a3982 100644
--- a/clang/lib/CodeGen/CodeGenModule.cpp
+++ b/clang/lib/CodeGen/CodeGenModule.cpp
@@ -730,6 +730,14 @@ static bool shouldAssumeDSOLocal(const CodeGenModule &CGM,
     return false;
 
   const llvm::Triple &TT = CGM.getTriple();
+  if (TT.isWindowsGNUEnvironment()) {
+    // In MinGW, variables without DLLImport can still be automatically
+    // imported from a DLL by the linker; don't mark variables that
+    // potentially could come from another DLL as DSO local.
+    if (GV->isDeclarationForLinker() && isa<llvm::GlobalVariable>(GV) &&
+        !GV->isThreadLocal())
+      return false;
+  }
   // Every other GV is local on COFF.
   // Make an exception for windows OS in the triple: Some firmware builds use
   // *-win32-macho triples. This (accidentally?) produced windows relocations
diff --git a/clang/test/CodeGen/dllimport.c b/clang/test/CodeGen/dllimport.c
index 61d69570526..c3fd0770ee8 100644
--- a/clang/test/CodeGen/dllimport.c
+++ b/clang/test/CodeGen/dllimport.c
@@ -39,7 +39,8 @@ USEVAR(GlobalRedecl2)
 
 // NB: MSVC issues a warning and makes GlobalRedecl3 dllexport. We follow GCC
 // and drop the dllimport with a warning.
-// CHECK: @GlobalRedecl3 = external dso_local global i32
+// MS: @GlobalRedecl3 = external dso_local global i32
+// GNU: @GlobalRedecl3 = external global i32
 __declspec(dllimport) extern int GlobalRedecl3;
                       extern int GlobalRedecl3; // dllimport ignored
 USEVAR(GlobalRedecl3)
diff --git a/clang/test/CodeGen/dso-local-executable.c b/clang/test/CodeGen/dso-local-executable.c
index 6e434a67eff..36fd4d0d039 100644
--- a/clang/test/CodeGen/dso-local-executable.c
+++ b/clang/test/CodeGen/dso-local-executable.c
@@ -9,6 +9,17 @@
 // COFF-DAG: @import_var = external dllimport global i32
 // COFF-DAG: declare dllimport void @import_func()
 
+// RUN: %clang_cc1 -triple x86_64-w64-mingw32 -emit-llvm %s -o - | FileCheck -allow-deprecated-dag-overlap --check-prefix=MINGW %s
+// MINGW-DAG: @bar = external global i32
+// MINGW-DAG: @weak_bar = extern_weak global i32
+// MINGW-DAG: declare dso_local void @foo()
+// MINGW-DAG: @baz = dso_local global i32 42
+// MINGW-DAG: define dso_local i32* @zed()
+// MINGW-DAG: @thread_var = external dso_local thread_local global i32
+// MINGW-DAG: @local_thread_var = dso_local thread_local global i32 42
+// MINGW-DAG: @import_var = external dllimport global i32
+// MINGW-DAG: declare dllimport void @import_func()
+
 // RUN: %clang_cc1 -triple x86_64-pc-linux -emit-llvm -mrelocation-model static %s -o - | FileCheck -allow-deprecated-dag-overlap --check-prefix=STATIC %s
 // STATIC-DAG: @bar = external dso_local global i32
 // STATIC-DAG: @weak_bar = extern_weak dso_local global i32
diff --git a/clang/test/CodeGenCXX/dllexport.cpp b/clang/test/CodeGenCXX/dllexport.cpp
index 5e4aa013b3c..392df84da10 100644
--- a/clang/test/CodeGenCXX/dllexport.cpp
+++ b/clang/test/CodeGenCXX/dllexport.cpp
@@ -43,7 +43,7 @@ __declspec(dllexport) extern int ExternGlobalDecl;
 
 // M64-DAG: @__ImageBase = external dso_local constant i8
 
-// GNU-DAG: @_ZTVN10__cxxabiv117__class_type_infoE = external dso_local global
+// GNU-DAG: @_ZTVN10__cxxabiv117__class_type_infoE = external global
 
 // dllexport implies a definition.
 // MSC-DAG: @"?GlobalDef@@3HA" = dso_local dllexport global i32 0, align 4
@@ -137,7 +137,7 @@ class __declspec(dllexport) i : h<> {};
 // Declarations are not exported.
 
 // MSC-DAG: @"??$VarTmplImplicitDef@UImplicitInst_Exported@@@@3HA" = external dso_local global
-// GNU-DAG: @_Z18VarTmplImplicitDefI21ImplicitInst_ExportedE          = external dso_local global
+// GNU-DAG: @_Z18VarTmplImplicitDefI21ImplicitInst_ExportedE          = external global
 template<typename T> __declspec(dllexport) extern int VarTmplImplicitDef;
 USEVAR(VarTmplImplicitDef<ImplicitInst_Exported>)
 
diff --git a/clang/test/CodeGenCXX/dllimport-members.cpp b/clang/test/CodeGenCXX/dllimport-members.cpp
index 7a7519f6683..f8034cfb47c 100644
--- a/clang/test/CodeGenCXX/dllimport-members.cpp
+++ b/clang/test/CodeGenCXX/dllimport-members.cpp
@@ -854,7 +854,7 @@ USEMV(MemVarTmpl, ImportedStaticVar<ExplicitSpec_Imported>)
 // Not importing specialization of a member variable template without explicit
 // dllimport.
 // MSC-DAG: @"??$ImportedStaticVar@UExplicitSpec_NotImported@@@MemVarTmpl@@2HB" = external dso_local constant i32
-// GNU-DAG: @_ZN10MemVarTmpl17ImportedStaticVarI24ExplicitSpec_NotImportedEE       = external dso_local constant i32
+// GNU-DAG: @_ZN10MemVarTmpl17ImportedStaticVarI24ExplicitSpec_NotImportedEE       = external constant i32
 template<> const int MemVarTmpl::ImportedStaticVar<ExplicitSpec_NotImported>;
 USEMV(MemVarTmpl, ImportedStaticVar<ExplicitSpec_NotImported>)
 
diff --git a/clang/test/CodeGenCXX/dllimport.cpp b/clang/test/CodeGenCXX/dllimport.cpp
index 74f58cc3b17..a6345be9adf 100644
--- a/clang/test/CodeGenCXX/dllimport.cpp
+++ b/clang/test/CodeGenCXX/dllimport.cpp
@@ -78,7 +78,7 @@ USEVAR(GlobalRedecl2c)
 // NB: MSC issues a warning and makes GlobalRedecl3 dllexport. We follow GCC
 // and drop the dllimport with a warning.
 // MSC-DAG: @"?GlobalRedecl3@@3HA" = external dso_local global i32
-// GNU-DAG: @GlobalRedecl3            = external dso_local global i32
+// GNU-DAG: @GlobalRedecl3            = external global i32
 __declspec(dllimport) extern int GlobalRedecl3;
                       extern int GlobalRedecl3; // dllimport ignored
 USEVAR(GlobalRedecl3)
@@ -137,7 +137,7 @@ template<typename T> __declspec(dllimport) int VarTmplRedecl2;
 USEVAR(VarTmplRedecl2<ImplicitInst_Imported>)
 
 // MSC-DAG: @"??$VarTmplRedecl3@UImplicitInst_Imported@@@@3HA" = external dso_local global i32
-// GNU-DAG: @_Z14VarTmplRedecl3I21ImplicitInst_ImportedE          = external dso_local global i32
+// GNU-DAG: @_Z14VarTmplRedecl3I21ImplicitInst_ImportedE          = external global i32
 template<typename T> __declspec(dllimport) extern int VarTmplRedecl3;
 template<typename T>                       extern int VarTmplRedecl3; // dllimport ignored
 USEVAR(VarTmplRedecl3<ImplicitInst_Imported>)
diff --git a/clang/test/CodeGenCXX/dso-local-executable.cpp b/clang/test/CodeGenCXX/dso-local-executable.cpp
index cc8d50f09c9..ceb649e074a 100644
--- a/clang/test/CodeGenCXX/dso-local-executable.cpp
+++ b/clang/test/CodeGenCXX/dso-local-executable.cpp
@@ -1,5 +1,6 @@
 // RUN: %clang_cc1 -triple x86_64-pc-linux -mrelocation-model static -O1 -emit-llvm %s -o - | FileCheck --check-prefix=STATIC %s
 // RUN: %clang_cc1 -triple x86_64-pc-linux -mrelocation-model static -fno-plt -O1 -emit-llvm %s -o - | FileCheck --check-prefix=NOPLT %s
+// RUN: %clang_cc1 -triple x86_64-w64-mingw32 -O1 -emit-llvm %s -o - | FileCheck --check-prefix=MINGW %s
 
 // STATIC-DAG: @_ZTV1C = linkonce_odr dso_local unnamed_addr constant
 // STATIC-DAG: @_ZTS1C = linkonce_odr dso_local constant
@@ -19,6 +20,15 @@
 // NOPLT-DAG: define dso_local void @_ZN1CC1Ev(
 // NOPLT-DAG: define linkonce_odr dso_local void @_ZN1C3fooEv(
 
+// MINGW-DAG: @_ZTV1C = linkonce_odr dso_local unnamed_addr constant
+// MINGW-DAG: @_ZTS1C = linkonce_odr dso_local constant
+// MINGW-DAG: @_ZTI1C = linkonce_odr dso_local constant
+// MINGW-DAG: @_ZZ14useStaticLocalvE3obj = linkonce_odr dso_local global
+// MINGW-DAG: @_ZGVZN5guard1gEvE1a = linkonce_odr dso_local global
+// MINGW-DAG: define dso_local void @_ZN1CC2Ev(
+// MINGW-DAG: define dso_local void @_ZN1CC1Ev(
+// MINGW-DAG: define linkonce_odr dso_local void @_ZN1C3fooEv(
+
 struct C {
   C();
   virtual void foo() {}
@@ -48,15 +58,23 @@ int h() {
 } // namespace guard
 
 
+// STATIC-DAG: @_ZN5test23barIiE1xE = available_externally dso_local constant i32
 // STATIC-DAG: define available_externally dso_local void @_ZN5test23barIcEC1Ev(
+// NOPLT-DAG: @_ZN5test23barIiE1xE = available_externally dso_local constant i32
 // NOPLT-DAG: define available_externally void @_ZN5test23barIcEC1Ev(
+// MINGW-DAG: @_ZN5test23barIiE1xE = available_externally constant i32
+// MINGW-DAG: define available_externally dso_local void @_ZN5test23barIcEC1Ev(
 namespace test2 {
 void foo();
 template <typename T>
 struct bar {
   virtual void zed();
+  static const int x = 42;
   bar() { foo(); }
 };
 extern template class bar<char>;
 bar<char> abc;
+const int *getX() {
+  return &bar<int>::x;
+}
 } // namespace test2