Allow TLS vars in dllimport/export functions; only inline dllimport f…

…unctions when safe (PR24593)

This patch does two things:

1) Don't error about dllimport/export on thread-local static local variables.
   We put those attributes on static locals in dllimport/export functions
   implicitly in case the function gets inlined. Now, for TLS variables this
   is a problem because we can't import such variables, but it's a benign
   problem becase:

2) Make sure we never inline a dllimport function TLS static locals. In fact,
   never inline a dllimport function that references a non-imported function
   or variable (because these are not defined in the importing library). This
   seems to match MSVC's behaviour.

Differential Revision: http://reviews.llvm.org/D12422

llvm-svn: 246338

clang/lib/CodeGen/CodeGenModule.cpp

@@ -1448,6 +1448,35 @@ namespace {
       return true;
     }
   };
+
+  struct DLLImportFunctionVisitor
+      : public RecursiveASTVisitor<DLLImportFunctionVisitor> {
+    bool SafeToInline = true;
+
+    bool VisitVarDecl(VarDecl *VD) {
+      // A thread-local variable cannot be imported.
+      SafeToInline = !VD->getTLSKind();
+      return SafeToInline;
+    }
+
+    // Make sure we're not referencing non-imported vars or functions.
+    bool VisitDeclRefExpr(DeclRefExpr *E) {
+      ValueDecl *VD = E->getDecl();
+      if (isa<FunctionDecl>(VD))
+        SafeToInline = VD->hasAttr<DLLImportAttr>();
+      else if (VarDecl *V = dyn_cast<VarDecl>(VD))
+        SafeToInline = !V->hasGlobalStorage() || V->hasAttr<DLLImportAttr>();
+      return SafeToInline;
+    }
+    bool VisitCXXDeleteExpr(CXXDeleteExpr *E) {
+      SafeToInline = E->getOperatorDelete()->hasAttr<DLLImportAttr>();
+      return SafeToInline;
+    }
+    bool VisitCXXNewExpr(CXXNewExpr *E) {
+      SafeToInline = E->getOperatorNew()->hasAttr<DLLImportAttr>();
+      return SafeToInline;
+    }
+  };
 }
 
 // isTriviallyRecursive - Check if this function calls another
@@ -1478,6 +1507,15 @@ CodeGenModule::shouldEmitFunction(GlobalDecl GD) {
   const auto *F = cast<FunctionDecl>(GD.getDecl());
   if (CodeGenOpts.OptimizationLevel == 0 && !F->hasAttr<AlwaysInlineAttr>())
     return false;
+
+  if (F->hasAttr<DLLImportAttr>()) {
+    // Check whether it would be safe to inline this dllimport function.
+    DLLImportFunctionVisitor Visitor;
+    Visitor.TraverseFunctionDecl(const_cast<FunctionDecl*>(F));
+    if (!Visitor.SafeToInline)
+      return false;
+  }
+
   // PR9614. Avoid cases where the source code is lying to us. An available
   // externally function should have an equivalent function somewhere else,
   // but a function that calls itself is clearly not equivalent to the real

clang/lib/Sema/SemaDecl.cpp

@@ -9967,9 +9967,17 @@ Sema::FinalizeDeclaration(Decl *ThisDecl) {
   // dllimport/dllexport variables cannot be thread local, their TLS index
   // isn't exported with the variable.
   if (DLLAttr && VD->getTLSKind()) {
-    Diag(VD->getLocation(), diag::err_attribute_dll_thread_local) << VD
-                                                                  << DLLAttr;
-    VD->setInvalidDecl();
+    FunctionDecl *F = dyn_cast<FunctionDecl>(VD->getDeclContext());
+    if (F && getDLLAttr(F)) {
+      assert(VD->isStaticLocal());
+      // But if this is a static local in a dlimport/dllexport function, the
+      // function will never be inlined, which means the var would never be
+      // imported, so having it marked import/export is safe.
+    } else {
+      Diag(VD->getLocation(), diag::err_attribute_dll_thread_local) << VD
+                                                                    << DLLAttr;
+      VD->setInvalidDecl();
+    }
   }
 
   if (UsedAttr *Attr = VD->getAttr<UsedAttr>()) {

clang/test/CodeGenCXX/dllimport.cpp

@@ -86,7 +86,7 @@ USEVAR(GlobalRedecl3)
 namespace ns { __declspec(dllimport) int ExternalGlobal; }
 USEVAR(ns::ExternalGlobal)
 
-int f();
+int __declspec(dllimport) f();
 // MO1-DAG: @"\01?x@?1??inlineStaticLocalsFunc@@YAHXZ@4HA" = available_externally dllimport global i32 0
 // MO1-DAG: @"\01??_B?1??inlineStaticLocalsFunc@@YAHXZ@51" = available_externally dllimport global i32 0
 inline int __declspec(dllimport) inlineStaticLocalsFunc() {
@@ -314,6 +314,46 @@ void UNIQ(use)() { ::operator new(42); }
 namespace ns { __declspec(dllimport) void externalFunc(); }
 USE(ns::externalFunc)
 
+// A dllimport function referencing non-imported vars or functions must not be available_externally.
+__declspec(dllimport) int ImportedVar;
+int NonImportedVar;
+__declspec(dllimport) int ImportedFunc();
+int NonImportedFunc();
+__declspec(dllimport) inline int ReferencingImportedVar() { return ImportedVar; }
+// MO1-DAG: define available_externally dllimport i32 @"\01?ReferencingImportedVar@@YAHXZ"
+__declspec(dllimport) inline int ReferencingNonImportedVar() { return NonImportedVar; }
+// MO1-DAG: declare dllimport i32 @"\01?ReferencingNonImportedVar@@YAHXZ"()
+__declspec(dllimport) inline int ReferencingImportedFunc() { return ImportedFunc(); }
+// MO1-DAG: define available_externally dllimport i32 @"\01?ReferencingImportedFunc@@YAHXZ"
+__declspec(dllimport) inline int ReferencingNonImportedFunc() { return NonImportedFunc(); }
+// MO1-DAG: declare dllimport i32 @"\01?ReferencingNonImportedFunc@@YAHXZ"()
+USE(ReferencingImportedVar)
+USE(ReferencingNonImportedVar)
+USE(ReferencingImportedFunc)
+USE(ReferencingNonImportedFunc)
+// References to operator new and delete count too, despite not being DeclRefExprs.
+__declspec(dllimport) inline int *ReferencingNonImportedNew() { return new int[2]; }
+// MO1-DAG: declare dllimport i32* @"\01?ReferencingNonImportedNew@@YAPAHXZ"
+__declspec(dllimport) inline int *ReferencingNonImportedDelete() { delete (int*)nullptr; }
+// MO1-DAG: declare dllimport i32* @"\01?ReferencingNonImportedDelete@@YAPAHXZ"
+USE(ReferencingNonImportedNew)
+USE(ReferencingNonImportedDelete)
+__declspec(dllimport) void* operator new[](__SIZE_TYPE__);
+__declspec(dllimport) void operator delete(void*);
+__declspec(dllimport) inline int *ReferencingImportedNew() { return new int[2]; }
+// MO1-DAG: define available_externally dllimport i32* @"\01?ReferencingImportedNew@@YAPAHXZ"
+__declspec(dllimport) inline int *ReferencingImportedDelete() { delete (int*)nullptr; }
+// MO1-DAG: define available_externally dllimport i32* @"\01?ReferencingImportedDelete@@YAPAHXZ"
+USE(ReferencingImportedNew)
+USE(ReferencingImportedDelete)
+
+// A dllimport function with a TLS variable must not be available_externally.
+__declspec(dllimport) inline void FunctionWithTLSVar() { static __thread int x = 42; }
+// MO1-DAG: declare dllimport void @"\01?FunctionWithTLSVar@@YAXXZ"
+__declspec(dllimport) inline void FunctionWithNormalVar() { static int x = 42; }
+// MO1-DAG: define available_externally dllimport void @"\01?FunctionWithNormalVar@@YAXXZ"
+USE(FunctionWithTLSVar)
+USE(FunctionWithNormalVar)
 
 
 //===----------------------------------------------------------------------===//

clang/test/SemaCXX/dllexport.cpp

@@ -71,6 +71,15 @@ __declspec(dllexport) auto ExternalAutoTypeGlobal = External();
 
 // Thread local variables are invalid.
 __declspec(dllexport) __thread int ThreadLocalGlobal; // expected-error{{'ThreadLocalGlobal' cannot be thread local when declared 'dllexport'}}
+inline void InlineWithThreadLocal() {
+  static __declspec(dllexport) __thread int ThreadLocalGlobal; // expected-error{{'ThreadLocalGlobal' cannot be thread local when declared 'dllexport'}}
+}
+
+// But if they're in a dllexport function, it's ok, because they will never get imported.
+inline void __declspec(dllexport) ExportedInlineWithThreadLocal() {
+  static __declspec(dllexport) __thread int OK1; // no-error
+  static __thread int OK2; // no-error
+}
 
 // Export in local scope.
 void functionScope() {

clang/test/SemaCXX/dllimport.cpp

@@ -93,6 +93,18 @@ __declspec(dllimport) auto InternalAutoTypeGlobal = Internal(); // expected-erro
 
 // Thread local variables are invalid.
 __declspec(dllimport) __thread int ThreadLocalGlobal; // expected-error{{'ThreadLocalGlobal' cannot be thread local when declared 'dllimport'}}
+inline void InlineWithThreadLocal() {
+  static __declspec(dllimport) __thread int ThreadLocalGlobal; // expected-error{{'ThreadLocalGlobal' cannot be thread local when declared 'dllimport'}}
+}
+
+// But if they're in a dllimported function, it's OK because we will not inline the function.
+// This doesn't work on MinGW, because there, dllimport on the inline function is ignored.
+#ifndef GNU
+inline void __declspec(dllimport) ImportedInlineWithThreadLocal() {
+  static __declspec(dllimport) __thread int OK1; // no-error
+  static __thread int OK2; // no-error
+}
+#endif
 
 // Import in local scope.
 __declspec(dllimport) float LocalRedecl1; // expected-note{{previous declaration is here}}