Add support for attribute 'trivial_abi'.

The 'trivial_abi' attribute can be applied to a C++ class, struct, or
union. It makes special functions of the annotated class (the destructor
and copy/move constructors) to be trivial for the purpose of calls and,
as a result, enables the annotated class or containing classes to be
passed or returned using the C ABI for the underlying type.

When a type that is considered trivial for the purpose of calls despite
having a non-trivial destructor (which happens only when the class type
or one of its subobjects is a 'trivial_abi' class) is passed to a
function, the callee is responsible for destroying the object.

For more background, see the discussions that took place on the mailing
list:

http://lists.llvm.org/pipermail/cfe-dev/2017-November/055955.html
http://lists.llvm.org/pipermail/cfe-commits/Week-of-Mon-20180101/thread.html#214043

rdar://problem/35204524

Differential Revision: https://reviews.llvm.org/D41039

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@324269 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 4 insertions, 0 deletions

diff --git a/lib/Sema/SemaTemplateInstantiate.cpp b/lib/Sema/SemaTemplateInstantiate.cpp
index a48e2466a8..313d99cf45 100644
--- a/lib/Sema/SemaTemplateInstantiate.cpp
+++ b/lib/Sema/SemaTemplateInstantiate.cpp
@@ -2108,6 +2108,10 @@ Sema::InstantiateClass(SourceLocation PointOfInstantiation,
     }
   }
 
+  // See if trivial_abi has to be dropped.
+  if (Instantiation && Instantiation->hasAttr<TrivialABIAttr>())
+    checkIllFormedTrivialABIStruct(*Instantiation);
+
   // Finish checking fields.
   ActOnFields(nullptr, Instantiation->getLocation(), Instantiation, Fields,
               SourceLocation(), SourceLocation(), nullptr);