[Sema] Diagnose default-initialization, destruction, and copying of

non-trivial C union types

This recommits r365985, which was reverted because it broke a few
projects using unions containing non-trivial ObjC pointer fields in
system headers. We now have a patch to fix the problem (see
https://reviews.llvm.org/D65256).

Original commit message:

This patch diagnoses uses of non-trivial C unions and structs/unions
containing non-trivial C unions in the following contexts, which require
default-initialization, destruction, or copying of the union objects,
instead of disallowing fields of non-trivial types in C unions, which is
what we currently do:

- function parameters.
- function returns.
- assignments.
- compound literals.
- block captures except capturing of `__block` variables by non-escaping blocks.
- local and global variable definitions.
- lvalue-to-rvalue conversions of volatile types.

See the discussion in https://reviews.llvm.org/D62988 for more background.

rdar://problem/50679094

Differential Revision: https://reviews.llvm.org/D63753

llvm-svn: 371275

1 files changed, 3 insertions, 0 deletions

diff --git a/clang/lib/AST/Decl.cpp b/clang/lib/AST/Decl.cpp
index 6c0c8281460..1d28f03b064 100644
--- a/clang/lib/AST/Decl.cpp
+++ b/clang/lib/AST/Decl.cpp
@@ -4268,6 +4268,9 @@ RecordDecl::RecordDecl(Kind DK, TagKind TK, const ASTContext &C,
   setNonTrivialToPrimitiveDefaultInitialize(false);
   setNonTrivialToPrimitiveCopy(false);
   setNonTrivialToPrimitiveDestroy(false);
+  setHasNonTrivialToPrimitiveDefaultInitializeCUnion(false);
+  setHasNonTrivialToPrimitiveDestructCUnion(false);
+  setHasNonTrivialToPrimitiveCopyCUnion(false);
   setParamDestroyedInCallee(false);
   setArgPassingRestrictions(APK_CanPassInRegs);
 }