[MS] Always use base dtors in place of complete/vbase dtors when possible

Summary:
Previously we tried too hard to uphold the fiction that destructor
variants work like they do on Itanium throughout the ABI-neutral parts
of clang. This lead to MS C++ ABI incompatiblities and other bugs. Now,
-mconstructor-aliases will no longer control this ABI detail, and clang
-cc1's LLVM IR output will be this much closer to the clang driver's.

Based on a patch by Zahira Ammarguellat:
  https://reviews.llvm.org/D39063

I've tried to move the logic that Zahira added into MicrosoftCXXABI.cpp.
There is only one ABI-specific detail sticking out, and that is in
CodeGenModule::getAddrOfCXXStructor, where we collapse complete dtors to
base dtors in the MS ABI.

This fixes PR32990.

Reviewers: erichkeane, zahiraam, majnemer, rjmccall

Subscribers: cfe-commits

Differential Revision: https://reviews.llvm.org/D44505

llvm-svn: 327732

1 files changed, 5 insertions, 13 deletions

diff --git a/clang/lib/CodeGen/CodeGenModule.cpp b/clang/lib/CodeGen/CodeGenModule.cpp
index 3c503eb66fa..cb1bfc143bf 100644
--- a/clang/lib/CodeGen/CodeGenModule.cpp
+++ b/clang/lib/CodeGen/CodeGenModule.cpp
@@ -786,12 +786,10 @@ void CodeGenModule::setDSOLocal(llvm::GlobalValue *GV) const {
 void CodeGenModule::setDLLImportDLLExport(llvm::GlobalValue *GV,
                                           GlobalDecl GD) const {
   const auto *D = dyn_cast<NamedDecl>(GD.getDecl());
+  // C++ destructors have a few C++ ABI specific special cases.
   if (const auto *Dtor = dyn_cast_or_null<CXXDestructorDecl>(D)) {
-    if (getCXXABI().useThunkForDtorVariant(Dtor, GD.getDtorType())) {
-      // Don't dllexport/import destructor thunks.
-      GV->setDLLStorageClass(llvm::GlobalValue::DefaultStorageClass);
-      return;
-    }
+    getCXXABI().setCXXDestructorDLLStorage(GV, Dtor, GD.getDtorType());
+    return;
   }
   setDLLImportDLLExport(GV, D);
 }
@@ -1074,14 +1072,8 @@ CodeGenModule::getFunctionLinkage(GlobalDecl GD) {
 
   GVALinkage Linkage = getContext().GetGVALinkageForFunction(D);
 
-  if (isa<CXXDestructorDecl>(D) &&
-      getCXXABI().useThunkForDtorVariant(cast<CXXDestructorDecl>(D),
-                                         GD.getDtorType())) {
-    // Destructor variants in the Microsoft C++ ABI are always internal or
-    // linkonce_odr thunks emitted on an as-needed basis.
-    return Linkage == GVA_Internal ? llvm::GlobalValue::InternalLinkage
-                                   : llvm::GlobalValue::LinkOnceODRLinkage;
-  }
+  if (const auto *Dtor = dyn_cast<CXXDestructorDecl>(D))
+    return getCXXABI().getCXXDestructorLinkage(Linkage, Dtor, GD.getDtorType());
 
   if (isa<CXXConstructorDecl>(D) &&
       cast<CXXConstructorDecl>(D)->isInheritingConstructor() &&