PR17576: Fix assertion on polymorphic classes with small alignment

We have to reserve at least the width of a pointer for the vfptr.  For
classes with small alignment, we weren't reserving enough space, and
were overlapping the first field with the vfptr.

llvm-svn: 192626

2 files changed, 13 insertions, 3 deletions

diff --git a/clang/lib/AST/RecordLayoutBuilder.cpp b/clang/lib/AST/RecordLayoutBuilder.cpp
index 05eeae1..b0230ac 100644
--- a/clang/lib/AST/RecordLayoutBuilder.cpp
+++ b/clang/lib/AST/RecordLayoutBuilder.cpp
@@ -2660,8 +2660,8 @@ void MicrosoftRecordLayoutBuilder::layoutVFPtr(const CXXRecordDecl *RD) {
   // the max alignment of all the non-virtual data in the class.  The resulting
   // layout is essentially { vftbl, { nvdata } }.  This is completely
   // unnecessary, but we're not here to pass judgment.
-  Size += Alignment;
   updateAlignment(PointerAlignment);
+  Size += Alignment;
 }
 
 void
diff --git a/clang/test/Layout/ms-x86-size-alignment-fail.cpp b/clang/test/Layout/ms-x86-size-alignment-fail.cpp
index c15d3825..6ce8a4b 100644
--- a/clang/test/Layout/ms-x86-size-alignment-fail.cpp
+++ b/clang/test/Layout/ms-x86-size-alignment-fail.cpp
@@ -58,10 +58,20 @@ struct E : virtual B0, virtual B1 {};
 // CHECK:    5 |   struct B1 (virtual base) (empty)
 // CHECK:      | [sizeof=8, align=4
 // CHECK:      |  nvsize=4, nvalign=4]
-	
+
+struct F { char a; virtual ~F(); };
+
+// CHECK: *** Dumping AST Record Layout
+// CHECK:    0 | struct F
+// CHECK:    0 |   (F vftable pointer)
+// CHECK:    4 |   char a
+// CHECK:      | [sizeof=8, align=4
+// CHECK:      |  nvsize=8, nvalign=4]
+
 int a[
 sizeof(A)+
 sizeof(B)+
 sizeof(C)+
 sizeof(D)+
-sizeof(E)];
+sizeof(E)+
+sizeof(F)];