[windows-itanium] Propagate DLL storage class to Initialisation Guard Variables

[bd1976llvm]

Summary

Initialisation Guard Variables should take their DLL storage class from the guarded variable. Otherwise, there will be a link error if the compiler inlines a reference to the guard variable into another module but that guard variable is not exported from the defining module.

This is required for platforms such as PlayStation and windows-itanium, that are aiming for source compatibility with MSVC w.r.t. dllimport/export annotations, given Clang's existing design which allows for inlining of a dllimport function as long as all the variables/functions referenced are also marked dllimport.

A similar change exists for the MSVC ABI: https://reviews.llvm.org/D4136.

I have added a run test for windows-itanium for this issue to the build recipe: https://reviews.llvm.org/D88124.

[compnerd]

The change itself seems fine, but the CI failure seems related to this change.

[probinson]

+cfe-commits

[bd1976llvm]

Fix for test failure on *nix.

[bd1976llvm]

In D138463#3944124, @compnerd wrote:

The change itself seems fine, but the CI failure seems related to this change.

Thanks. There's been renewed interest in using DLLs with C++ interfaces so we should, hopefully, be able to put some effort into improving the support.

clang/lib/CodeGen/ItaniumCXXABI.cpp

if (!guard) {
     // Mangle the name for the guard.
     SmallString<256> guardName;
     {
       llvm::raw_svector_ostream out(guardName);
       getMangleContext().mangleStaticGuardVariable(&D, out);
     }
 
     // Create the guard variable with a zero-initializer.
-    // Just absorb linkage and visibility from the guarded variable.
+    // Just absorb linkage, visibility and dll storage class  from the guarded
+    // variable.
     guard = new llvm::GlobalVariable(CGM.getModule(), guardTy,
                                      false, var->getLinkage(),
                                      llvm::ConstantInt::get(guardTy, 0),
                                      guardName.str());
     guard->setDSOLocal(var->isDSOLocal());
     guard->setVisibility(var->getVisibility());
+    guard->setDLLStorageClass(var->getDLLStorageClass());
     // If the variable is thread-local, so is its guard variable.
     guard->setThreadLocalMode(var->getThreadLocalMode());
     guard->setAlignment(guardAlignment.getAsAlign());
 
     // The ABI says: "It is suggested that it be emitted in the same COMDAT
     // group as the associated data object." In practice, this doesn't work for
     // non-ELF and non-Wasm object formats, so only do it for ELF and Wasm.
     llvm::Comdat *C = var->getComdat();

clang/test/CodeGenCXX/windows-itanium-init-guard.cpp

+// Initialisation Guard Variables should take their DLL storage class from
+// the guarded variable. Otherwise, there will be a link error if the compiler
+// inlines a reference to the guard variable into another module but that
+// guard variable is not exported from the defining module.
+
+// RUN: %clang_cc1 -emit-llvm -triple i686-windows-itanium -fdeclspec %s -O1 -disable-llvm-passes -o - -DAPI= | FileCheck %s --check-prefixes=NONE
+// RUN: %clang_cc1 -emit-llvm -triple i686-windows-itanium -fdeclspec %s -O1 -disable-llvm-passes -o - -DAPI="__declspec(dllexport)" | FileCheck %s --check-prefixes=EXPORT
+// RUN: %clang_cc1 -emit-llvm -triple i686-windows-itanium -fdeclspec %s -O1 -disable-llvm-passes -o - -DAPI="__declspec(dllimport)" | FileCheck %s --check-prefixes=IMPORT
+
+// RUN: %clang_cc1 -emit-llvm -triple x86_64-scei-ps4 -fdeclspec %s -O1 -disable-llvm-passes -o - -DAPI= | FileCheck %s --check-prefixes=NONE
+// RUN: %clang_cc1 -emit-llvm -triple x86_64-scei-ps4 -fdeclspec %s -O1 -disable-llvm-passes -o - -DAPI="__declspec(dllexport)" | FileCheck %s --check-prefixes=EXPORT
+// RUN: %clang_cc1 -emit-llvm -triple x86_64-scei-ps4 -fdeclspec %s -O1 -disable-llvm-passes -o - -DAPI="__declspec(dllimport)" | FileCheck %s --check-prefixes=IMPORT
+
+// RUN: %clang_cc1 -emit-llvm -triple x86_64-scei-ps5 -fdeclspec %s -O1 -disable-llvm-passes -o - -DAPI= | FileCheck %s --check-prefixes=NONE
+// RUN: %clang_cc1 -emit-llvm -triple x86_64-scei-ps5 -fdeclspec %s -O1 -disable-llvm-passes -o - -DAPI="__declspec(dllexport)" | FileCheck %s --check-prefixes=EXPORT
+// RUN: %clang_cc1 -emit-llvm -triple x86_64-scei-ps5 -fdeclspec %s -O1 -disable-llvm-passes -o - -DAPI="__declspec(dllimport)" | FileCheck %s --check-prefixes=IMPORT
+
+//NONE: @_ZZN3foo3GetEvE9Singleton = linkonce_odr {{(dso_local )?}}global
+//NONE: @_ZGVZN3foo3GetEvE9Singleton = linkonce_odr {{(dso_local )?}}global
+
+//EXPORT: @_ZZN3foo3GetEvE9Singleton = weak_odr {{(dso_local )?}}dllexport global
+//EXPORT: @_ZGVZN3foo3GetEvE9Singleton = weak_odr {{(dso_local )?}}dllexport global
+
+//IMPORT: @_ZZN3foo3GetEvE9Singleton = available_externally dllimport global
+//IMPORT: @_ZGVZN3foo3GetEvE9Singleton = available_externally dllimport global
+
+struct API foo {
+  foo() {}
+  static void Get() { static foo Singleton; }
+};
+
+void f() { foo::Get(); }