[MS-ABI] Update virtual base padding rules to match MSVC 10+

In version 9 (VS2010) (and prior)? versions of msvc, if the last field 
in a record was a bitfield padding equal to the size of the storage 
class of that bitfield was added before each vbase and vtordisp.  This 
patch removes that feature from clang and updates the lit tests to 
reflect it. 

llvm-svn: 206004

3 files changed, 24 insertions, 31 deletions

diff --git a/clang/lib/AST/RecordLayoutBuilder.cpp b/clang/lib/AST/RecordLayoutBuilder.cpp
index 1ea2be41b3b..02fbcf0a4ad 100644
--- a/clang/lib/AST/RecordLayoutBuilder.cpp
+++ b/clang/lib/AST/RecordLayoutBuilder.cpp
@@ -2091,9 +2091,6 @@ 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, 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
@@ -2595,10 +2592,6 @@ void MicrosoftRecordLayoutBuilder::layoutVirtualBases(const CXXRecordDecl *RD) {
     const CXXRecordDecl *BaseDecl = I.getType()->getAsCXXRecordDecl();
     const ASTRecordLayout &BaseLayout = Context.getASTRecordLayout(BaseDecl);
     bool HasVtordisp = HasVtordispSet.count(BaseDecl);
-    // 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;
     // Insert padding between two bases if the left first one is zero sized or
     // contains a zero sized subobject and the right is zero sized or one leads
     // with a zero sized base.  The padding between virtual bases is 4
diff --git a/clang/test/Layout/ms-x86-bitfields-vbases.cpp b/clang/test/Layout/ms-x86-bitfields-vbases.cpp
index 7cffa8c8e4a..5b54596bbb8 100644
--- a/clang/test/Layout/ms-x86-bitfields-vbases.cpp
+++ b/clang/test/Layout/ms-x86-bitfields-vbases.cpp
@@ -13,17 +13,17 @@ struct A : virtual B0 { char a : 1; };
 // CHECK-NEXT:    0 | struct A
 // CHECK-NEXT:    0 |   (A vbtable pointer)
 // CHECK-NEXT:    4 |   char a
-// CHECK-NEXT:   12 |   struct B0 (virtual base)
-// CHECK-NEXT:   12 |     int a
-// CHECK-NEXT:      | [sizeof=16, align=4
+// CHECK-NEXT:    8 |   struct B0 (virtual base)
+// CHECK-NEXT:    8 |     int a
+// CHECK-NEXT:      | [sizeof=12, align=4
 // CHECK-NEXT:      |  nvsize=8, nvalign=4]
 // CHECK-X64: *** Dumping AST Record Layout
 // CHECK-X64: *** Dumping AST Record Layout
 // CHECK-X64-NEXT:    0 | struct A
 // CHECK-X64-NEXT:    0 |   (A vbtable pointer)
 // CHECK-X64-NEXT:    8 |   char a
-// CHECK-X64-NEXT:   20 |   struct B0 (virtual base)
-// CHECK-X64-NEXT:   20 |     int a
+// CHECK-X64-NEXT:   16 |   struct B0 (virtual base)
+// CHECK-X64-NEXT:   16 |     int a
 // CHECK-X64-NEXT:      | [sizeof=24, align=8
 // CHECK-X64-NEXT:      |  nvsize=16, nvalign=8]
 
@@ -33,16 +33,16 @@ struct B : virtual B0 { short a : 1; };
 // CHECK-NEXT:    0 | struct B
 // CHECK-NEXT:    0 |   (B vbtable pointer)
 // CHECK-NEXT:    4 |   short a
-// CHECK-NEXT:   12 |   struct B0 (virtual base)
-// CHECK-NEXT:   12 |     int a
-// CHECK-NEXT:      | [sizeof=16, align=4
+// CHECK-NEXT:    8 |   struct B0 (virtual base)
+// CHECK-NEXT:    8 |     int a
+// CHECK-NEXT:      | [sizeof=12, align=4
 // CHECK-NEXT:      |  nvsize=8, nvalign=4]
 // CHECK-X64: *** Dumping AST Record Layout
 // CHECK-X64-NEXT:    0 | struct B
 // CHECK-X64-NEXT:    0 |   (B vbtable pointer)
 // CHECK-X64-NEXT:    8 |   short a
-// CHECK-X64-NEXT:   20 |   struct B0 (virtual base)
-// CHECK-X64-NEXT:   20 |     int a
+// CHECK-X64-NEXT:   16 |   struct B0 (virtual base)
+// CHECK-X64-NEXT:   16 |     int a
 // CHECK-X64-NEXT:      | [sizeof=24, align=8
 // CHECK-X64-NEXT:      |  nvsize=16, nvalign=8]
 
@@ -94,22 +94,22 @@ struct E : virtual B0, virtual B1 { long long : 1; };
 // CHECK-NEXT:    0 | struct E
 // CHECK-NEXT:    0 |   (E vbtable pointer)
 // CHECK-NEXT:    8 |   long long
-// CHECK-NEXT:   24 |   struct B0 (virtual base)
-// CHECK-NEXT:   24 |     int a
-// CHECK-NEXT:   36 |   struct B1 (virtual base)
-// CHECK-NEXT:   36 |     int a
-// CHECK-NEXT:      | [sizeof=40, align=8
+// CHECK-NEXT:   16 |   struct B0 (virtual base)
+// CHECK-NEXT:   16 |     int a
+// CHECK-NEXT:   20 |   struct B1 (virtual base)
+// CHECK-NEXT:   20 |     int a
+// CHECK-NEXT:      | [sizeof=24, align=8
 // CHECK-NEXT:      |  nvsize=16, nvalign=8]
 // CHECK-X64: *** Dumping AST Record Layout
 // CHECK-X64: *** Dumping AST Record Layout
 // CHECK-X64-NEXT:    0 | struct E
 // CHECK-X64-NEXT:    0 |   (E vbtable pointer)
 // CHECK-X64-NEXT:    8 |   long long
-// CHECK-X64-NEXT:   24 |   struct B0 (virtual base)
-// CHECK-X64-NEXT:   24 |     int a
-// CHECK-X64-NEXT:   36 |   struct B1 (virtual base)
-// CHECK-X64-NEXT:   36 |     int a
-// CHECK-X64-NEXT:      | [sizeof=40, align=8
+// CHECK-X64-NEXT:   16 |   struct B0 (virtual base)
+// CHECK-X64-NEXT:   16 |     int a
+// CHECK-X64-NEXT:   20 |   struct B1 (virtual base)
+// CHECK-X64-NEXT:   20 |     int a
+// CHECK-X64-NEXT:      | [sizeof=24, align=8
 // CHECK-X64-NEXT:      |  nvsize=16, nvalign=8]
 
 int a[
diff --git a/clang/test/Layout/ms-x86-pack-and-align.cpp b/clang/test/Layout/ms-x86-pack-and-align.cpp
index 0843b3e0bfe..be0499c2cbb 100644
--- a/clang/test/Layout/ms-x86-pack-and-align.cpp
+++ b/clang/test/Layout/ms-x86-pack-and-align.cpp
@@ -473,7 +473,7 @@ struct RE {
 // CHECK-NEXT:    0 | struct RB2
 // CHECK-NEXT:    0 |   (RB2 vbtable pointer)
 // CHECK-NEXT: 1024 |   int b
-// CHECK-NEXT: 1032 |   struct RA (virtual base) (empty)
+// CHECK-NEXT: 1028 |   struct RA (virtual base) (empty)
 // CHECK-NEXT:      | [sizeof=1032, align=1024
 // CHECK-NEXT:      |  nvsize=1028, nvalign=1024]
 // CHECK: *** Dumping AST Record Layout
@@ -481,7 +481,7 @@ struct RE {
 // CHECK-NEXT:    0 |   (RB3 vftable pointer)
 // CHECK-NEXT: 1024 |   (RB3 vbtable pointer)
 // CHECK-NEXT: 2048 |   int b
-// CHECK-NEXT: 2056 |   struct RA (virtual base) (empty)
+// CHECK-NEXT: 2052 |   struct RA (virtual base) (empty)
 // CHECK-NEXT:      | [sizeof=2056, align=1024
 // CHECK-NEXT:      |  nvsize=2052, nvalign=1024]
 // CHECK: *** Dumping AST Record Layout
@@ -516,7 +516,7 @@ struct RE {
 // CHECK-X64-NEXT:    0 | struct RB2
 // CHECK-X64-NEXT:    0 |   (RB2 vbtable pointer)
 // CHECK-X64-NEXT: 1024 |   int b
-// CHECK-X64-NEXT: 1032 |   struct RA (virtual base) (empty)
+// CHECK-X64-NEXT: 1028 |   struct RA (virtual base) (empty)
 // CHECK-X64-NEXT:      | [sizeof=1032, align=1024
 // CHECK-X64-NEXT:      |  nvsize=1028, nvalign=1024]
 // CHECK-X64: *** Dumping AST Record Layout
@@ -524,7 +524,7 @@ struct RE {
 // CHECK-X64-NEXT:    0 |   (RB3 vftable pointer)
 // CHECK-X64-NEXT: 1024 |   (RB3 vbtable pointer)
 // CHECK-X64-NEXT: 2048 |   int b
-// CHECK-X64-NEXT: 2056 |   struct RA (virtual base) (empty)
+// CHECK-X64-NEXT: 2052 |   struct RA (virtual base) (empty)
 // CHECK-X64-NEXT:      | [sizeof=2056, align=1024
 // CHECK-X64-NEXT:      |  nvsize=2052, nvalign=1024]
 // CHECK-X64: *** Dumping AST Record Layout