[MS-ABI] adds padding before all vbases after a bitfield

 
MS-ABI adds padding before *every* vbase if the last field in a record 
is a bit-field. This changes clangs behavior to match. I also fix some 
windows-style line endings in the test file.

Differential Revision: http://llvm-reviews.chandlerc.com/D2277

llvm-svn: 196605

2 files changed, 99 insertions, 68 deletions

diff --git a/clang/lib/AST/RecordLayoutBuilder.cpp b/clang/lib/AST/RecordLayoutBuilder.cpp
index ec791564893..b692025aa0f 100644
--- a/clang/lib/AST/RecordLayoutBuilder.cpp
+++ b/clang/lib/AST/RecordLayoutBuilder.cpp
@@ -2014,9 +2014,9 @@ static bool isMsLayout(const RecordDecl* D) {
 //   one.
 // * The last zero size virtual base may be placed at the end of the struct.
 //   and can potentially alias a zero sized type in the next struct.
-// * If the last field is a non-zero length bitfield and we have any virtual
-//   bases then some extra padding is added before the virtual bases for no
-//   obvious reason.
+// * If the last field is a non-zero length bitfield, all virtual bases will
+//   have extra padding added before them for no obvious reason.  The padding
+//   has the same number of bits as the type of the bitfield.
 // * When laying out empty non-virtual bases, an extra byte of padding is added
 //   if the non-virtual base before the empty non-virtual base has a vbptr.
 // * The ABI attempts to avoid aliasing of zero sized bases by adding padding
@@ -2558,17 +2558,16 @@ void MicrosoftRecordLayoutBuilder::layoutVirtualBases(const CXXRecordDecl *RD) {
   llvm::SmallPtrSet<const CXXRecordDecl *, 2> HasVtordisp =
       computeVtorDispSet(RD);
 
-  // If the last field we laid out was a non-zero length bitfield then add some
-  // extra padding for no obvious reason.
-  if (LastFieldIsNonZeroWidthBitfield)
-    Size += CurrentBitfieldSize;
-
   // Iterate through the virtual bases and lay them out.
   for (CXXRecordDecl::base_class_const_iterator i = RD->vbases_begin(),
                                                 e = RD->vbases_end();
        i != e; ++i) {
     const CXXRecordDecl *BaseDecl =
         cast<CXXRecordDecl>(i->getType()->castAs<RecordType>()->getDecl());
+    // If the last field we laid out was a non-zero length bitfield then add
+    // some extra padding for no obvious reason.
+    if (LastFieldIsNonZeroWidthBitfield)
+      Size += CurrentBitfieldSize;
     layoutVirtualBase(BaseDecl, HasVtordisp.count(BaseDecl));
   }
 }
diff --git a/clang/test/Layout/ms-x86-bitfields-vbases.cpp b/clang/test/Layout/ms-x86-bitfields-vbases.cpp
index e11ef67a634..f973edd6a3e 100644
--- a/clang/test/Layout/ms-x86-bitfields-vbases.cpp
+++ b/clang/test/Layout/ms-x86-bitfields-vbases.cpp
@@ -3,82 +3,114 @@
 // RUN: %clang_cc1 -fno-rtti -emit-llvm-only -triple x86_64-pc-win32 -fdump-record-layouts -fsyntax-only -cxx-abi microsoft %s 2>/dev/null \
 // RUN:            | FileCheck %s -check-prefix CHECK-X64
 
-struct B0 { };

-

-struct A : virtual B0 { char a : 1; };

+struct B0 { int a; };
+struct B1 { int a; };
 
-// CHECK: *** Dumping AST Record Layout

-// CHECK:    0 | struct A

-// CHECK:    0 |   (A vbtable pointer)

-// CHECK:    4 |   char a

-// CHECK:    9 |   struct B0 (virtual base) (empty)

-// CHECK:      | [sizeof=9, align=4

-// CHECK:      |  nvsize=8, nvalign=4]

+struct A : virtual B0 { char a : 1; };
+
+// CHECK: *** Dumping AST Record Layout
+// CHECK:    0 | struct A
+// CHECK:    0 |   (A vbtable pointer)
+// CHECK:    4 |   char a
+// CHECK:   12 |   struct B0 (virtual base)
+// CHECK:   12 |     int a
+// CHECK:      | [sizeof=16, align=4
+// CHECK:      |  nvsize=8, nvalign=4]
 // CHECK-X64: *** Dumping AST Record Layout
-// CHECK-X64:    0 | struct A

-// CHECK-X64:    0 |   (A vbtable pointer)

-// CHECK-X64:    8 |   char a

-// CHECK-X64:   17 |   struct B0 (virtual base) (empty)

-// CHECK-X64:      | [sizeof=24, align=8

-// CHECK-X64:      |  nvsize=16, nvalign=8]

+// CHECK-X64:    0 | struct A
+// CHECK-X64:    0 |   (A vbtable pointer)
+// CHECK-X64:    8 |   char a
+// CHECK-X64:   20 |   struct B0 (virtual base)
+// CHECK-X64:   20 |     int a
+// CHECK-X64:      | [sizeof=24, align=8
+// CHECK-X64:      |  nvsize=16, nvalign=8]
 
-struct B : virtual B0 { short a : 1; };

+struct B : virtual B0 { short a : 1; };
 
 // CHECK: *** Dumping AST Record Layout
-// CHECK:    0 | struct B

-// CHECK:    0 |   (B vbtable pointer)

-// CHECK:    4 |   short a

-// CHECK:   10 |   struct B0 (virtual base) (empty)

-// CHECK:      | [sizeof=10, align=4

-// CHECK:      |  nvsize=8, nvalign=4]

+// CHECK:    0 | struct B
+// CHECK:    0 |   (B vbtable pointer)
+// CHECK:    4 |   short a
+// CHECK:   12 |   struct B0 (virtual base)
+// CHECK:   12 |     int a
+// CHECK:      | [sizeof=16, align=4
+// CHECK:      |  nvsize=8, nvalign=4]
 // CHECK-X64: *** Dumping AST Record Layout
-// CHECK-X64:    0 | struct B

-// CHECK-X64:    0 |   (B vbtable pointer)

-// CHECK-X64:    8 |   short a

-// CHECK-X64:   18 |   struct B0 (virtual base) (empty)

-// CHECK-X64:      | [sizeof=24, align=8

-// CHECK-X64:      |  nvsize=16, nvalign=8]

+// CHECK-X64:    0 | struct B
+// CHECK-X64:    0 |   (B vbtable pointer)
+// CHECK-X64:    8 |   short a
+// CHECK-X64:   20 |   struct B0 (virtual base)
+// CHECK-X64:   20 |     int a
+// CHECK-X64:      | [sizeof=24, align=8
+// CHECK-X64:      |  nvsize=16, nvalign=8]
 
-struct C : virtual B0 { char a : 1; char : 0; };

+struct C : virtual B0 { char a : 1; char : 0; };
 
 // CHECK: *** Dumping AST Record Layout
-// CHECK:    0 | struct C

-// CHECK:    0 |   (C vbtable pointer)

-// CHECK:    4 |   char a

-// CHECK:    5 |   char

-// CHECK:    8 |   struct B0 (virtual base) (empty)

-// CHECK:      | [sizeof=8, align=4

-// CHECK:      |  nvsize=8, nvalign=4]

+// CHECK:    0 | struct C
+// CHECK:    0 |   (C vbtable pointer)
+// CHECK:    4 |   char a
+// CHECK:    5 |   char
+// CHECK:    8 |   struct B0 (virtual base)
+// CHECK:    8 |     int a
+// CHECK:      | [sizeof=12, align=4
+// CHECK:      |  nvsize=8, nvalign=4]
 // CHECK-X64: *** Dumping AST Record Layout
-// CHECK-X64:    0 | struct C

-// CHECK-X64:    0 |   (C vbtable pointer)

-// CHECK-X64:    8 |   char a

-// CHECK-X64:    9 |   char

-// CHECK-X64:   16 |   struct B0 (virtual base) (empty)

-// CHECK-X64:      | [sizeof=16, align=8

-// CHECK-X64:      |  nvsize=16, nvalign=8]

+// CHECK-X64:    0 | struct C
+// CHECK-X64:    0 |   (C vbtable pointer)
+// CHECK-X64:    8 |   char a
+// CHECK-X64:    9 |   char
+// CHECK-X64:   16 |   struct B0 (virtual base)
+// CHECK-X64:   16 |     int a
+// CHECK-X64:      | [sizeof=24, align=8
+// CHECK-X64:      |  nvsize=16, nvalign=8]
+
+struct D : virtual B0 { char a : 1; char b; };
 
-struct D : virtual B0 { char a : 1; char b; };

+// CHECK: *** Dumping AST Record Layout
+// CHECK:    0 | struct D
+// CHECK:    0 |   (D vbtable pointer)
+// CHECK:    4 |   char a
+// CHECK:    5 |   char b
+// CHECK:    8 |   struct B0 (virtual base)
+// CHECK:    8 |     int a
+// CHECK:      | [sizeof=12, align=4
+// CHECK:      |  nvsize=8, nvalign=4]
+// CHECK-X64: *** Dumping AST Record Layout
+// CHECK-X64:    0 | struct D
+// CHECK-X64:    0 |   (D vbtable pointer)
+// CHECK-X64:    8 |   char a
+// CHECK-X64:    9 |   char b
+// CHECK-X64:   16 |   struct B0 (virtual base)
+// CHECK-X64:   16 |     int a
+// CHECK-X64:      | [sizeof=24, align=8
+// CHECK-X64:      |  nvsize=16, nvalign=8]
 
+struct E : virtual B0, virtual B1 { long long : 1; };
 // CHECK: *** Dumping AST Record Layout
-// CHECK:    0 | struct D

-// CHECK:    0 |   (D vbtable pointer)

-// CHECK:    4 |   char a

-// CHECK:    5 |   char b

-// CHECK:    8 |   struct B0 (virtual base) (empty)

-// CHECK:      | [sizeof=8, align=4

-// CHECK:      |  nvsize=8, nvalign=4]

+// CHECK:    0 | struct E
+// CHECK:    0 |   (E vbtable pointer)
+// CHECK:    8 |   long long
+// CHECK:   24 |   struct B0 (virtual base)
+// CHECK:   24 |     int a
+// CHECK:   36 |   struct B1 (virtual base)
+// CHECK:   36 |     int a
+// CHECK:      | [sizeof=40, align=8
+// CHECK:      |  nvsize=16, nvalign=8]
 // CHECK-X64: *** Dumping AST Record Layout
-// CHECK-X64:    0 | struct D

-// CHECK-X64:    0 |   (D vbtable pointer)

-// CHECK-X64:    8 |   char a

-// CHECK-X64:    9 |   char b

-// CHECK-X64:   16 |   struct B0 (virtual base) (empty)

-// CHECK-X64:      | [sizeof=16, align=8

-// CHECK-X64:      |  nvsize=16, nvalign=8]

+// CHECK-X64:    0 | struct E
+// CHECK-X64:    0 |   (E vbtable pointer)
+// CHECK-X64:    8 |   long long
+// CHECK-X64:   24 |   struct B0 (virtual base)
+// CHECK-X64:   24 |     int a
+// CHECK-X64:   36 |   struct B1 (virtual base)
+// CHECK-X64:   36 |     int a
+// CHECK-X64:      | [sizeof=40, align=8
+// CHECK-X64:      |  nvsize=16, nvalign=8]
 
 int a[
 sizeof(A)+
 sizeof(B)+
 sizeof(C)+
-sizeof(D)];
+sizeof(D)+
+sizeof(E)];