[ms-abi] Leading VFPtrs don't suppress the leading zero sized flag

The MS-ABI tracks a bit that asserts that the first sub-object is zero 
sized.  This bit is used to add padding between objects if there's the 
potential for zero sized objects to alias.  The bit is still true even 
if the zero sized base is lead by a VFPtr.  This patch makes clang mimic 
that behavior.

llvm-svn: 199132

1 files changed, 44 insertions, 0 deletions

diff --git a/clang/test/Layout/ms-x86-alias-avoidance-padding.cpp b/clang/test/Layout/ms-x86-alias-avoidance-padding.cpp
index 48249137017..3112b39c9bc 100644
--- a/clang/test/Layout/ms-x86-alias-avoidance-padding.cpp
+++ b/clang/test/Layout/ms-x86-alias-avoidance-padding.cpp
@@ -255,10 +255,54 @@ struct F : virtual D, virtual B {};
 // CHECK-X64-NEXT:      | [sizeof=32, align=8
 // CHECK-X64-NEXT:      |  nvsize=8, nvalign=8]
 
+struct JC0 {
+	JC0() { printf("JC0 : %d\n", (int)((char*)this - buffer)); }
+};
+struct JC1 : JC0 {
+	virtual void f() {}
+	JC1() { printf("JC1 : %d\n", (int)((char*)this - buffer)); }
+};
+struct JC2 : JC1 {
+	JC2() { printf("JC2 : %d\n", (int)((char*)this - buffer)); }
+};
+struct JC4 : JC1, JC2 {
+	JC4() { printf("JC4 : %d\n", (int)((char*)this - buffer)); }
+};
+
+// CHECK: *** Dumping AST Record Layout
+// CHECK: *** Dumping AST Record Layout
+// CHECK: *** Dumping AST Record Layout
+// CHECK: *** Dumping AST Record Layout
+// CHECK-NEXT:    0 | struct JC4
+// CHECK-NEXT:    0 |   struct JC1 (primary base)
+// CHECK-NEXT:    0 |     (JC1 vftable pointer)
+// CHECK-NEXT:    4 |     struct JC0 (base) (empty)
+// CHECK-NEXT:    8 |   struct JC2 (base)
+// CHECK-NEXT:    8 |     struct JC1 (primary base)
+// CHECK-NEXT:    8 |       (JC1 vftable pointer)
+// CHECK-NEXT:   12 |       struct JC0 (base) (empty)
+// CHECK-NEXT:      | [sizeof=12, align=4
+// CHECK-NEXT:      |  nvsize=12, nvalign=4]
+// CHECK-x64: *** Dumping AST Record Layout
+// CHECK-x64: *** Dumping AST Record Layout
+// CHECK-x64: *** Dumping AST Record Layout
+// CHECK-x64: *** Dumping AST Record Layout
+// CHECK-x64-NEXT:    0 | struct JC4
+// CHECK-x64-NEXT:    0 |   struct JC1 (primary base)
+// CHECK-x64-NEXT:    0 |     (JC1 vftable pointer)
+// CHECK-x64-NEXT:    8 |     struct JC0 (base) (empty)
+// CHECK-x64-NEXT:   16 |   struct JC2 (base)
+// CHECK-x64-NEXT:   16 |     struct JC1 (primary base)
+// CHECK-x64-NEXT:   16 |       (JC1 vftable pointer)
+// CHECK-x64-NEXT:   24 |       struct JC0 (base) (empty)
+// CHECK-x64-NEXT:      | [sizeof=24, align=8
+// CHECK-x64-NEXT:      |  nvsize=24, nvalign=8]
+
 int a[
 sizeof(AT3) +
 sizeof(BT3) +
 sizeof(T3) +
 sizeof(E) +
 sizeof(F) +
+sizeof(JC4) +
 0];