Windows: Make implicit dllimport more selective

* Newly require `-link-defaultlib-shared` for implicit dllimport.
  E.g., this enables to compile druntime DLL with `-fvisibility=public`
  for pure exports and no (local) imports (such as builtin TypeInfos).
* `-link-defaultlib-shared` alone now only implicitly imports symbols
  from druntime/Phobos.
  This simplifies building complex DLLs linked against a bunch of
  static libs (dub only supports static lib dependencies!); the static
  libs don't need to be compiled with `-fvisibility=public` anymore
  (if the DLL itself isn't either), `-link-defaultlib-shared` is
  sufficient.
  This is mainly useful for existing DLLs with explicit exports, to make
  them link against *shared* druntime/Phobos and so end up with a single
  druntime/Phobos for the whole process.

dmd/globals.d

@@ -109,6 +109,14 @@ enum FeatureState : byte
     enabled = 1    /// Specified as `-preview=`
 }
 
+version (IN_LLVM)
+enum DLLImport : byte
+{
+    none,
+    defaultLibsOnly, // only symbols from druntime/Phobos
+    all
+}
+
 // Put command line switches in here
 extern (C++) struct Param
 {
@@ -305,7 +313,7 @@ version (IN_LLVM)
 
     // Windows-specific:
     bool dllexport;      // dllexport ~all defined symbols?
-    bool dllimport; // dllimport data symbols not defined in any root module?
+    DLLImport dllimport; // dllimport data symbols not defined in any root module?
 } // IN_LLVM
 }
 

dmd/globals.h

@@ -98,6 +98,15 @@ enum class FeatureState : signed char
     enabled = 1    /// Specified as `-preview=`
 };
 
+#if IN_LLVM
+enum class DLLImport : char
+{
+    none,
+    defaultLibsOnly, // only symbols from druntime/Phobos
+    all
+};
+#endif
+
 // Put command line switches in here
 struct Param
 {
@@ -280,7 +289,7 @@ struct Param
 
     // Windows-specific:
     bool dllexport;      // dllexport ~all defined symbols?
-    bool dllimport; // dllimport data symbols not defined in any root module?
+    DLLImport dllimport; // dllimport data symbols not defined in any root module?
 #endif
 };
 

dmd/id.h

@@ -44,6 +44,9 @@ struct Id
     static Identifier *dcompute;
     static Identifier *dcPointer;
     static Identifier *object;
+    static Identifier *core;
+    static Identifier *etc;
+    static Identifier *std;
     static Identifier *ensure;
     static Identifier *require;
     static Identifier *xopEquals;

driver/main.cpp

@@ -1090,10 +1090,10 @@ int cppmain() {
         v == opts::SymbolVisibility::public_ ||
         // default with -shared
         (v == opts::SymbolVisibility::default_ && global.params.dll);
-    global.params.dllimport =
-        v == opts::SymbolVisibility::public_ ||
-        // enforced when linking against shared default libs
-        linkAgainstSharedDefaultLibs();
+    global.params.dllimport = !linkAgainstSharedDefaultLibs() ? DLLImport::none
+                              : v == opts::SymbolVisibility::public_
+                                  ? DLLImport::all
+                                  : DLLImport::defaultLibsOnly;
   }
 
   // allocate the target abi

gen/llvmhelpers.cpp

@@ -1670,6 +1670,22 @@ std::string llvmTypeToString(llvm::Type *type) {
   return result;
 }
 
+bool isDefaultLibSymbol(Dsymbol *sym) {
+  auto mod = sym->getModule();
+  if (!mod)
+    return false;
+
+  auto md = mod->md;
+  if (!md)
+    return false;
+
+  if (md->packages.length == 0)
+    return md->id == Id::object;
+
+  auto p = md->packages.ptr[0];
+  return p == Id::core || p == Id::std || p == Id::etc || p == Id::ldc;
+}
+
 llvm::GlobalVariable *declareGlobal(const Loc &loc, llvm::Module &module,
                                     llvm::Type *type,
                                     llvm::StringRef mangledName,

gen/llvmhelpers.h

@@ -245,6 +245,9 @@ LLConstant *toConstantArray(LLType *ct, LLArrayType *at, T *str, size_t len,
 
 llvm::Constant *buildStringLiteralConstant(StringExp *se, bool zeroTerm);
 
+/// Is the specified symbol part of druntime/Phobos?
+bool isDefaultLibSymbol(Dsymbol *sym);
+
 /// Tries to declare an LLVM global. If a variable with the same mangled name
 /// already exists, checks if the types match and returns it instead.
 ///

gen/modules.cpp

@@ -190,8 +190,9 @@ LLFunction *build_module_reference_and_ctor(const char *moduleMangle,
   LLConstant *mref = gIR->module.getNamedGlobal(mrefIRMangle);
   LLType *modulerefPtrTy = getPtrToType(modulerefTy);
   if (!mref) {
-    mref = declareGlobal(Loc(), gIR->module, modulerefPtrTy, mrefIRMangle,
-                         false, false, global.params.dllimport);
+    mref =
+        declareGlobal(Loc(), gIR->module, modulerefPtrTy, mrefIRMangle, false,
+                      false, global.params.dllimport != DLLImport::none);
   }
   mref = DtoBitCast(mref, getPtrToType(modulerefPtrTy));
 

gen/optimizer.cpp

@@ -423,7 +423,7 @@ bool ldc_optimize_module(llvm::Module *M) {
 
   addOptimizationPasses(mpm, fpm, optLevel(), sizeLevel());
 
-  if (global.params.dllimport) {
+  if (global.params.dllimport != DLLImport::none) {
     mpm.add(createDLLImportRelocationPass());
   }
 

gen/typinf.cpp

@@ -439,8 +439,7 @@ void buildTypeInfo(TypeInfoDeclaration *decl) {
     // immutable on the D side, and e.g. synchronized() can be used on the
     // implicit monitor.
     const bool isConstant = false;
-    // TODO: no dllimport when compiling druntime itself
-    const bool useDLLImport = isBuiltin && global.params.dllimport;
+    bool useDLLImport = isBuiltin && global.params.dllimport != DLLImport::none;
     gvar = declareGlobal(decl->loc, gIR->module, type, irMangle, isConstant,
                          false, useDLLImport);
   }

ir/iraggr.cpp

@@ -56,7 +56,9 @@ bool IrAggr::useDLLImport() const {
   if (!global.params.targetTriple->isOSWindows())
     return false;
 
-  if (global.params.dllimport || aggrdecl->isExport()) {
+  if (aggrdecl->isExport() || global.params.dllimport == DLLImport::all ||
+      (global.params.dllimport == DLLImport::defaultLibsOnly &&
+       isDefaultLibSymbol(aggrdecl))) {
     // dllimport, unless defined in a root module (=> no extra indirection for
     // other root modules, assuming *all* root modules will be linked together
     // to one or more binaries).

ir/irmodule.cpp

@@ -27,7 +27,11 @@ llvm::GlobalVariable *IrModule::moduleInfoSymbol() {
 
   const auto irMangle = getIRMangledModuleInfoSymbolName(M);
 
-  const bool useDLLImport = global.params.dllimport && !M->isRoot();
+  bool useDLLImport = false;
+  if (global.params.dllimport == DLLImport::all)
+    useDLLImport = !M->isRoot();
+  else if (global.params.dllimport == DLLImport::defaultLibsOnly)
+    useDLLImport = !M->isRoot() && isDefaultLibSymbol(M);
 
   moduleInfoVar = declareGlobal(Loc(), gIR->module,
                                 llvm::StructType::create(gIR->context()),

ir/irvar.cpp

@@ -85,9 +85,13 @@ void IrGlobal::declare() {
   if (global.params.targetTriple->isOSWindows()) {
     // dllimport isn't supported for thread-local globals (MSVC++ neither)
     if (!V->isThreadlocal()) {
-      // with -fvisibility=public / -link-defaultlib-shared, also include all
+      // with -fvisibility=public / -link-defaultlib-shared, also include
       // extern(D) globals
-      if (V->isExport() || (global.params.dllimport && V->linkage == LINK::d)) {
+      if (V->isExport() ||
+          (V->linkage == LINK::d &&
+           (global.params.dllimport == DLLImport::all ||
+            (global.params.dllimport == DLLImport::defaultLibsOnly &&
+             isDefaultLibSymbol(V))))) {
         const bool isDefinedInRootModule =
             !(V->storage_class & STCextern) && !V->inNonRoot();
         if (!isDefinedInRootModule)

runtime/CMakeLists.txt

@@ -708,7 +708,7 @@ macro(build_runtime_variant d_flags c_flags ld_flags lib_suffix path_suffix emit
        AND NOT ${all_d_files_at_once})
         set(phobos2_o "")
         set(phobos2_bc "")
-        compile_phobos2("${phobos2_d_flags};-relocation-model=pic;-fvisibility=public"
+        compile_phobos2("${phobos2_d_flags};-relocation-model=pic;-fvisibility=public;-link-defaultlib-shared"
                         "${lib_suffix}${SHARED_LIB_SUFFIX}" "${path_suffix}"
                         "${emit_bc}" "${all_d_files_at_once}" "OFF" phobos2_o phobos2_bc)
 
@@ -761,7 +761,7 @@ macro(build_runtime_variant d_flags c_flags ld_flags lib_suffix path_suffix emit
         if(phobos2_common STREQUAL "")
             set(phobos2_o "")
             set(phobos2_bc "")
-            compile_phobos2("${phobos2_d_flags};-relocation-model=pic;-fvisibility=public"
+            compile_phobos2("${phobos2_d_flags};-relocation-model=pic;-fvisibility=public;-link-defaultlib-shared"
                             "${lib_suffix}${SHARED_LIB_SUFFIX}" "${path_suffix}"
                             "OFF" "${all_d_files_at_once}" "${all_d_files_at_once}" phobos2_o phobos2_bc)
         endif()

runtime/druntime

@@ -1 +1 @@
-Subproject commit 65a26b5756fd1b4f693b013e1838ac11ac2e19d4
+Subproject commit c424142bbab8def67d362ac18d534c2be165d39b

tests/codegen/fvisibility_dll.d

@@ -4,11 +4,12 @@
 
 // REQUIRES: Windows
 
-// generate DLL and import lib
+// generate DLL and import lib (public visibility by default)
 // RUN: %ldc %S/inputs/fvisibility_dll_lib.d -betterC -shared -of=%t_lib.dll
 
-// compile, link and run the app; -link-defaultlib-shared for importing data symbols as dllimport
-// RUN: %ldc %s -I%S/inputs -betterC -link-defaultlib-shared %t_lib.lib -of=%t.exe
+// compile, link and run the app;
+// `-link-defaultlib-shared -fvisibility=public` for dllimporting data symbols
+// RUN: %ldc %s -I%S/inputs -betterC -link-defaultlib-shared -fvisibility=public %t_lib.lib -of=%t.exe
 // RUN: %t.exe
 
 import fvisibility_dll_lib;