MS ABI: Up the required alignment after inserting padding between vbases

We would correctly insert sufficiently aligned padding between vbases
when our leading base was empty, however we would neglect to increase
the required alignment of the most derived class.

This fixes PR20315.

llvm-svn: 213123

2 files changed, 58 insertions, 1 deletions

diff --git a/clang/lib/AST/RecordLayoutBuilder.cpp b/clang/lib/AST/RecordLayoutBuilder.cpp
index 3c91360fb61..b5ebbee83b5 100644
--- a/clang/lib/AST/RecordLayoutBuilder.cpp
+++ b/clang/lib/AST/RecordLayoutBuilder.cpp
@@ -2613,8 +2613,10 @@ void MicrosoftRecordLayoutBuilder::layoutVirtualBases(const CXXRecordDecl *RD) {
     // bytes (in both 32 and 64 bits modes) and always involves rounding up to
     // the required alignment, we don't know why.
     if ((PreviousBaseLayout && PreviousBaseLayout->hasZeroSizedSubObject() &&
-        BaseLayout.leadsWithZeroSizedBase()) || HasVtordisp)
+        BaseLayout.leadsWithZeroSizedBase()) || HasVtordisp) {
       Size = Size.RoundUpToAlignment(VtorDispAlignment) + VtorDispSize;
+      RequiredAlignment = VtorDispAlignment;
+    }
     // Insert the virtual base.
     ElementInfo Info = getAdjustedElementInfo(BaseLayout);
     CharUnits BaseOffset = Size.RoundUpToAlignment(Info.Alignment);
diff --git a/clang/test/Layout/ms-x86-pack-and-align.cpp b/clang/test/Layout/ms-x86-pack-and-align.cpp
index be0499c2cbb..73984652aeb 100644
--- a/clang/test/Layout/ms-x86-pack-and-align.cpp
+++ b/clang/test/Layout/ms-x86-pack-and-align.cpp
@@ -544,6 +544,60 @@ struct RE {
 // CHECK-X64-NEXT:      | [sizeof=1029, align=1
 // CHECK-X64-NEXT:      |  nvsize=1029, nvalign=1]
 
+struct NA {};
+struct NB {};
+#pragma pack(push, 1)
+struct NC : virtual NA, virtual NB {};
+#pragma pack(pop)
+struct ND : NC {};
+
+// CHECK: *** Dumping AST Record Layout
+// CHECK-NEXT:    0 | struct NA (empty)
+// CHECK-NEXT:      | [sizeof=1, align=1
+// CHECK-NEXT:      |  nvsize=0, nvalign=1]
+// CHECK: *** Dumping AST Record Layout
+// CHECK-NEXT:    0 | struct NB (empty)
+// CHECK-NEXT:      | [sizeof=1, align=1
+// CHECK-NEXT:      |  nvsize=0, nvalign=1]
+// CHECK: *** Dumping AST Record Layout
+// CHECK-NEXT:    0 | struct NC
+// CHECK-NEXT:    0 |   (NC vbtable pointer)
+// CHECK-NEXT:    4 |   struct NA (virtual base) (empty)
+// CHECK-NEXT:    8 |   struct NB (virtual base) (empty)
+// CHECK-NEXT:      | [sizeof=8, align=1
+// CHECK-NEXT:      |  nvsize=4, nvalign=1]
+// CHECK: *** Dumping AST Record Layout
+// CHECK-NEXT:    0 | struct ND
+// CHECK-NEXT:    0 |   struct NC (base)
+// CHECK-NEXT:    0 |     (NC vbtable pointer)
+// CHECK-NEXT:    4 |   struct NA (virtual base) (empty)
+// CHECK-NEXT:    8 |   struct NB (virtual base) (empty)
+// CHECK-NEXT:      | [sizeof=8, align=4
+// CHECK-NEXT:      |  nvsize=4, nvalign=4]
+// CHECK-X64: *** Dumping AST Record Layout
+// CHECK-X64-NEXT:    0 | struct NA (empty)
+// CHECK-X64-NEXT:      | [sizeof=1, align=1
+// CHECK-X64-NEXT:      |  nvsize=0, nvalign=1]
+// CHECK-X64: *** Dumping AST Record Layout
+// CHECK-X64-NEXT:    0 | struct NB (empty)
+// CHECK-X64-NEXT:      | [sizeof=1, align=1
+// CHECK-X64-NEXT:      |  nvsize=0, nvalign=1]
+// CHECK-X64: *** Dumping AST Record Layout
+// CHECK-X64-NEXT:    0 | struct NC
+// CHECK-X64-NEXT:    0 |   (NC vbtable pointer)
+// CHECK-X64-NEXT:    8 |   struct NA (virtual base) (empty)
+// CHECK-X64-NEXT:   12 |   struct NB (virtual base) (empty)
+// CHECK-X64-NEXT:      | [sizeof=12, align=1
+// CHECK-X64-NEXT:      |  nvsize=8, nvalign=1]
+// CHECK-X64: *** Dumping AST Record Layout
+// CHECK-X64-NEXT:    0 | struct ND
+// CHECK-X64-NEXT:    0 |   struct NC (base)
+// CHECK-X64-NEXT:    0 |     (NC vbtable pointer)
+// CHECK-X64-NEXT:    8 |   struct NA (virtual base) (empty)
+// CHECK-X64-NEXT:   12 |   struct NB (virtual base) (empty)
+// CHECK-X64-NEXT:      | [sizeof=12, align=4
+// CHECK-X64-NEXT:      |  nvsize=8, nvalign=4]
+
 int a[
 sizeof(X)+
 sizeof(Y)+
@@ -568,4 +622,5 @@ sizeof(RB2)+
 sizeof(RB3)+
 sizeof(RC)+
 sizeof(RE)+
+sizeof(ND)+
 0];