Fixing PR18510 by checking whether the non-virtual base of the derived class

might have a smaller size as compared to the stand-alone type of the base class.
This is possible when the derived class is packed and hence might have smaller
alignment requirement than the base class.

Differential Revision: http://llvm-reviews.chandlerc.com/D2599



git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@200031 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CodeGen/CGRecordLayoutBuilder.cpp

@@ -558,7 +558,12 @@ bool CGRecordLayoutBuilder::LayoutBase(const CXXRecordDecl *base,
   if (getTypeAlignment(subobjectType) > Alignment)
     return false;
 
-  AppendField(baseOffset, subobjectType);
+  if (LastLaidOutBase.NonVirtualSize < CharUnits::fromQuantity(
+      Types.getDataLayout().getStructLayout(subobjectType)->getSizeInBytes()))
+    AppendBytes(LastLaidOutBase.NonVirtualSize);
+  else
+    AppendField(baseOffset, subobjectType);
+
   return true;
 }
 

test/CodeGenCXX/pragma-pack-3.cpp

+// RUN: %clang_cc1 %s -triple=i686-apple-darwin10 -emit-llvm -o - | FileCheck %s
+
+struct Base {
+  char a;
+};
+
+struct Derived_1 : virtual Base
+{
+  char b;
+};
+
+#pragma pack(1)
+struct Derived_2 : Derived_1 {
+  // CHECK: %struct.Derived_2 = type <{ [5 x i8], %struct.Base }>
+};
+
+Derived_2 x;