[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, 0 deletions

diff --git a/clang/lib/CodeGen/CGCXX.cpp b/clang/lib/CodeGen/CGCXX.cpp
index 738c635d26f..dfae7d5f5f7 100644
--- a/clang/lib/CodeGen/CGCXX.cpp
+++ b/clang/lib/CodeGen/CGCXX.cpp
@@ -242,6 +242,11 @@ llvm::Constant *CodeGenModule::getAddrOfCXXStructor(
   if (auto *CD = dyn_cast<CXXConstructorDecl>(MD)) {
     GD = GlobalDecl(CD, toCXXCtorType(Type));
   } else {
+    // Always alias equivalent complete destructors to base destructors in the
+    // MS ABI.
+    if (getTarget().getCXXABI().isMicrosoft() &&
+        Type == StructorType::Complete && MD->getParent()->getNumVBases() == 0)
+      Type = StructorType::Base;
     GD = GlobalDecl(cast<CXXDestructorDecl>(MD), toCXXDtorType(Type));
   }