MS ABI: adding template static member in the linker directive section to make sure init function can be called before main.

[jyu2]

Summary

A MS only run time problem, because the init function for template static member is not getting called when the template static member is not reference. To be able to evoke the init function, MS put the template static member in the linker directive section, that cause init function gets call. As Reid suggest; add template static data member to llvm.used that cause compiler to emit a similar -include directive into the linker directive section.

The bug is report in:
//bugs.llvm.org/show_bug.cgi?id=40323

[rnk]

Apparently I wrote this comment long ago and never hit send.

lib/CodeGen/CGDeclCXX.cpp

484

We might really want isOSBinFormatCOFF, since I think the same issue affects Windows Itanium with -OPT:REF and LLD.

[rnk]

lgtm

lib/CodeGen/CGDeclCXX.cpp

484

On reflection, it's probably best not to mess with mingw for now. Let's just commit this as is.

[jyu2]

In D58160#1433458, @rnk wrote:

lgtm

Thank you so much Reid!

[jyu2]

Closed by commit rG0b28b8b09be7: Bug-40323: MS ABI adding template static member in the linker directive section… (authored by jyu2).

lib/CodeGen/CGDeclCXX.cpp

if (D->getTLSKind()) {
     //
     // As a consequence, we can put them into their own llvm.global_ctors entry.
     //
     // If the global is externally visible, put the initializer into a COMDAT
     // group with the global being initialized.  On most platforms, this is a
     // minor startup time optimization.  In the MS C++ ABI, there are no guard
     // variables, so this COMDAT key is required for correctness.
     AddGlobalCtor(Fn, 65535, COMDATKey);
+    if (getTarget().getCXXABI().isMicrosoft()) {
+      // In The MS C++, MS add template static data member in the linker
+      // drective.
+      assert(COMDATKey);
+      addUsedGlobal(COMDATKey);
+    }
   } else if (D->hasAttr<SelectAnyAttr>()) {
     // SelectAny globals will be comdat-folded. Put the initializer into a
     // COMDAT group associated with the global, so the initializers get folded
     // too.
     AddGlobalCtor(Fn, 65535, COMDATKey);
   } else {
     I = DelayedCXXInitPosition.find(D); // Re-do lookup in case of re-hash.
     if (I == DelayedCXXInitPosition.end()) {

test/CodeGenCXX/microsoft-abi-template-static-init.cpp

+// RUN: %clang_cc1 %s -triple=i686-pc-win32 -fms-extensions -emit-llvm -o - | FileCheck %s
+// RUN: %clang_cc1 %s -triple=x86_64-pc-win32 -fms-extensions -emit-llvm -o - | FileCheck %s
+// RUN: %clang_cc1 %s -triple=i686-pc-windows-msvc -fms-extensions -emit-llvm -o - | FileCheck %s
+// RUN: %clang_cc1 %s -triple=x86_64-pc-windows-msvc -fms-extensions -emit-llvm -o - | FileCheck %s
+
+struct S {
+  S();
+  ~S();
+};
+
+template <typename T> struct __declspec(dllexport) ExportedTemplate {
+  static S s;
+};
+template <typename T> S ExportedTemplate<T>::s;
+void useExportedTemplate(ExportedTemplate<int> x) {
+  (void)x.s;
+}
+int f();
+namespace selectany_init {
+// MS don't put selectany static var in the linker directive, init routine
+// f() is not getting called if x is not referenced.
+int __declspec(selectany) x = f();
+}
+
+namespace explicit_template_instantiation {
+template <typename T> struct A { static  int x; };
+template <typename T> int A<T>::x = f();
+template struct A<int>;
+}
+
+namespace implicit_template_instantiation {
+template <typename T> struct A { static  int x; };
+template <typename T>  int A<T>::x = f();
+int g() { return A<int>::x; }
+}
+
+
+template <class T>
+struct X_ {
+  static T ioo;
+  static T init();
+};
+template <class T> T X_<T>::ioo = X_<T>::init();
+template struct X_<int>;
+
+template <class T>
+struct X {
+  static T ioo;
+  static T init();
+};
+// template specialized static data don't need in llvm.used,
+// the static init routine get call from _GLOBAL__sub_I_ routines.
+template <> int X<int>::ioo = X<int>::init();
+template struct X<int>;
+// CHECK: @llvm.global_ctors = appending global [6 x { i32, void ()*, i8* }] [{ i32, void ()*, i8* } { i32 65535, void ()* @"??__Ex@selectany_init@@YAXXZ", i8* bitcast (i32* @"?x@selectany_init@@3HA" to i8*) }, { i32, void ()*, i8* } { i32 65535, void ()* @"??__E?x@?$A@H@explicit_template_instantiation@@2HA@@YAXXZ", i8* bitcast (i32* @"?x@?$A@H@explicit_template_instantiation@@2HA" to i8*) }, { i32, void ()*, i8* } { i32 65535, void ()* @"??__E?ioo@?$X_@H@@2HA@@YAXXZ", i8* bitcast (i32* @"?ioo@?$X_@H@@2HA" to i8*) }, { i32, void ()*, i8* } { i32 65535, void ()* @"??__E?s@?$ExportedTemplate@H@@2US@@A@@YAXXZ", i8* getelementptr inbounds (%struct.S, %struct.S* @"?s@?$ExportedTemplate@H@@2US@@A", i32 0, i32 0) }, { i32, void ()*, i8* } { i32 65535, void ()* @"??__E?x@?$A@H@implicit_template_instantiation@@2HA@@YAXXZ", i8* bitcast (i32* @"?x@?$A@H@implicit_template_instantiation@@2HA" to i8*) }, { i32, void ()*, i8* } { i32 65535, void ()* @_GLOBAL__sub_I_microsoft_abi_template_static_init.cpp, i8* null }]
+// CHECK: @llvm.used = appending global [4 x i8*] [i8* bitcast (i32* @"?x@?$A@H@explicit_template_instantiation@@2HA" to i8*), i8* bitcast (i32* @"?ioo@?$X_@H@@2HA" to i8*), i8* getelementptr inbounds (%struct.S, %struct.S* @"?s@?$ExportedTemplate@H@@2US@@A", i32 0, i32 0), i8* bitcast (i32* @"?x@?$A@H@implicit_template_instantiation@@2HA" to i8*)], section "llvm.metadata"
+