Correctly handle zero-sized but non-empty base classes in IRGen.

Fixes rdar://20621065.

A more elegant fix would preclude this case by defining the
rules such that zero-size classes are always formally empty.
I believe the only extensions which create zero-size classes
right now are flexible arrays and zero-length arrays; it's
not abstractly unreasonable to say that those don't count
as members for the purposes of emptiness, just as zero-width
bitfields don't count.  But that's an ABI-affecting change
and requires further discussion; in the meantime, let's not
assert / miscompile.

llvm-svn: 235815

1 files changed, 5 insertions, 1 deletions

diff --git a/clang/lib/CodeGen/CGRecordLayoutBuilder.cpp b/clang/lib/CodeGen/CGRecordLayoutBuilder.cpp
index 202ea972f8d..c33d2d9f86d 100644
--- a/clang/lib/CodeGen/CGRecordLayoutBuilder.cpp
+++ b/clang/lib/CodeGen/CGRecordLayoutBuilder.cpp
@@ -438,8 +438,12 @@ void CGRecordLowering::accumulateBases() {
   for (const auto &Base : RD->bases()) {
     if (Base.isVirtual())
       continue;
+
+    // Bases can be zero-sized even if not technically empty if they
+    // contain only a trailing array member.
     const CXXRecordDecl *BaseDecl = Base.getType()->getAsCXXRecordDecl();
-    if (!BaseDecl->isEmpty())
+    if (!BaseDecl->isEmpty() &&
+        !Context.getASTRecordLayout(BaseDecl).getSize().isZero())
       Members.push_back(MemberInfo(Layout.getBaseClassOffset(BaseDecl),
           MemberInfo::Base, getStorageType(BaseDecl), BaseDecl));
   }