[MSABI] Remove comdat attribute for inheriting ctor.

Currently, for MS, the linkage for the inheriting constructors is set to
internal.  However, the comdat attribute is also set like:

define internal noundef ptr @"??0?$B@_N@@qeaa@AEBVF@@aebua@@@z"(ptr noundef nonnull returned align 1 dereferenceable(1) %this, ptr noundef nonnull align 1 dereferenceable(1) %0, ptr noundef nonnull align 1 dereferenceable(1) %1) unnamed_addr comdat

This could cause linker to fail.

The change is to remove comdat attribute for the inheriting constructor
to make linker happy.

Differential Revision: https://reviews.llvm.org/D158538

Author: jyu2-git

clang/lib/AST/ASTContext.cpp

@@ -11688,6 +11688,14 @@ static GVALinkage basicGVALinkageForFunction(const ASTContext &Context,
   if (FD->isMSExternInline())
     return GVA_StrongODR;
 
+  if (Context.getTargetInfo().getCXXABI().isMicrosoft() &&
+      isa<CXXConstructorDecl>(FD) &&
+      cast<CXXConstructorDecl>(FD)->isInheritingConstructor())
+    // Our approach to inheriting constructors is fundamentally different from
+    // that used by the MS ABI, so keep our inheriting constructor thunks
+    // internal rather than trying to pick an unambiguous mangling for them.
+    return GVA_Internal;
+
   return GVA_DiscardableODR;
 }
 

clang/lib/CodeGen/CodeGenModule.cpp

@@ -1970,15 +1970,6 @@ CodeGenModule::getFunctionLinkage(GlobalDecl GD) {
   if (const auto *Dtor = dyn_cast<CXXDestructorDecl>(D))
     return getCXXABI().getCXXDestructorLinkage(Linkage, Dtor, GD.getDtorType());
 
-  if (isa<CXXConstructorDecl>(D) &&
-      cast<CXXConstructorDecl>(D)->isInheritingConstructor() &&
-      Context.getTargetInfo().getCXXABI().isMicrosoft()) {
-    // Our approach to inheriting constructors is fundamentally different from
-    // that used by the MS ABI, so keep our inheriting constructor thunks
-    // internal rather than trying to pick an unambiguous mangling for them.
-    return llvm::GlobalValue::InternalLinkage;
-  }
-
   return getLLVMLinkageForDeclarator(D, Linkage);
 }
 

clang/test/CodeGenCXX/ms-inheriting-ctor.cpp

@@ -0,0 +1,49 @@
+// RUN: %clang_cc1 -fcxx-exceptions -triple=x86_64-windows-msvc -emit-llvm %s -o - | FileCheck %s
+
+class F {
+public:
+  F(wchar_t *);
+};
+using a = F;
+struct A {};
+struct b {
+  b(a, F, A);
+};
+template <typename, typename> struct c : b {
+  c(const a &p1, const A &d) : b(p1, 0, d) {}
+};
+template <typename e> struct B : c<e, b> {
+  using c<e, b>::c;
+};
+class f {
+public:
+  f(...);
+}
+
+typedef g;
+class C {
+public:
+  C(g, f);
+};
+static wchar_t h;
+class D {
+public:
+  static C E();
+};
+
+C D::E() {
+  C i(B<bool>(&h, {}), f());
+  return i;
+}
+
+// Inheriting ctor has internal linkage without comdat.
+
+// CHECK-LABEL: define internal noundef ptr @"??0?$B@_N@@QEAA@AEBVF@@AEBUA@@@Z"
+// CHECK-NOT:comdat
+// CHECK-SAME: {{\{$}}
+
+// non-inheriting ctro should has linkonce_odr with comdat attribute.
+
+// CHECK-LABEL: define linkonce_odr dso_local noundef ptr @"??0?$c@_NUb@@@@QEAA@AEBVF@@AEBUA@@@Z"
+// CHECK:comdat
+// CHECK-SAME: {{\{$}}