Hi majnemer, rsmith,
Microsoft adds an extra byte of padding before laying out zero sized
non-virtual bases if the non-virtual base before it contains a vbptr.
Addresses:
http://llvm.org/bugs/show_bug.cgi?id=17750
http://llvm-reviews.chandlerc.com/D2106
Files:
lib/AST/RecordLayoutBuilder.cpp
test/Layout/ms-x86-shared-vb-lazy-empty-nonvirtual-base.cpp
Index: lib/AST/RecordLayoutBuilder.cpp
===================================================================
--- lib/AST/RecordLayoutBuilder.cpp
+++ lib/AST/RecordLayoutBuilder.cpp
@@ -2014,6 +2014,9 @@
// 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.
+// * 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.
+
namespace {
struct MicrosoftRecordLayoutBuilder {
@@ -2135,6 +2138,8 @@
bool LastBaseWasEmpty;
/// \brief Lets us know if we're in 64-bit mode
bool Is64BitMode;
+ /// \brief True if the last non-virtual base has a vbptr.
+ bool LastNonVirtualBaseHasVBPtr;
};
} // namespace
@@ -2314,6 +2319,7 @@
MicrosoftRecordLayoutBuilder::layoutNonVirtualBases(const CXXRecordDecl *RD) {
LazyEmptyBase = 0;
LastBaseWasEmpty = false;
+ LastNonVirtualBaseHasVBPtr = false;
// Lay out the primary base first.
if (PrimaryBase)
@@ -2341,6 +2347,10 @@
const ASTRecordLayout &LazyLayout =
Context.getASTRecordLayout(LazyEmptyBase);
Size = Size.RoundUpToAlignment(LazyLayout.getAlignment());
+ // If the last non-virtual base has a vbptr we add a byte of padding for no
+ // obvious reason.
+ if (LastNonVirtualBaseHasVBPtr)
+ Size++;
Bases.insert(std::make_pair(LazyEmptyBase, Size));
// Empty bases only consume space when followed by another empty base.
if (RD && Layout->getNonVirtualSize().isZero()) {
@@ -2348,6 +2358,7 @@
Size++;
}
LazyEmptyBase = 0;
+ LastNonVirtualBaseHasVBPtr = false;
}
// RD is null when flushing the final lazy base.
@@ -2366,6 +2377,7 @@
// Note: we don't update alignment here because it was accounted
// for during initalization.
LastBaseWasEmpty = false;
+ LastNonVirtualBaseHasVBPtr = Layout->hasVBPtr();
}
void MicrosoftRecordLayoutBuilder::layoutVBPtr(const CXXRecordDecl *RD) {
Index: test/Layout/ms-x86-shared-vb-lazy-empty-nonvirtual-base.cpp
===================================================================
--- /dev/null
+++ test/Layout/ms-x86-shared-vb-lazy-empty-nonvirtual-base.cpp
@@ -0,0 +1,216 @@
+// RUN: %clang_cc1 -fno-rtti -emit-llvm-only -triple i686-pc-win32 -fdump-record-layouts -cxx-abi microsoft %s 2>/dev/null \
+// RUN: | FileCheck %s
+// RUN: %clang_cc1 -fno-rtti -emit-llvm-only -triple x86_64-pc-win32 -fdump-record-layouts -cxx-abi microsoft %s 2>/dev/null \
+// RUN: | FileCheck %s -check-prefix CHECK-X64
+
+
+struct U { char a; };
+struct V { };
+struct W { };
+struct X : virtual V { char a; };
+struct Y : virtual V { char a; };
+struct Z : Y { };
+
+struct A : X, W { char a; };
+
+// CHECK: *** Dumping AST Record Layout
+// CHECK: 0 | struct A
+// CHECK: 0 | struct X (base)
+// CHECK: 0 | (X vbtable pointer)
+// CHECK: 4 | char a
+// CHECK: 9 | struct W (base) (empty)
+// CHECK: 9 | char a
+// CHECK: 12 | struct V (virtual base) (empty)
+// CHECK: | [sizeof=12, align=4
+// CHECK: | nvsize=12, nvalign=4]
+// CHECK-X64: *** Dumping AST Record Layout
+// CHECK-X64: 0 | struct A
+// CHECK-X64: 0 | struct X (base)
+// CHECK-X64: 0 | (X vbtable pointer)
+// CHECK-X64: 8 | char a
+// CHECK-X64: 17 | struct W (base) (empty)
+// CHECK-X64: 17 | char a
+// CHECK-X64: 24 | struct V (virtual base) (empty)
+// CHECK-X64: | [sizeof=24, align=8
+// CHECK-X64: | nvsize=24, nvalign=8]
+
+struct B : X, U, W { char a; };
+
+// CHECK: *** Dumping AST Record Layout
+// CHECK: 0 | struct B
+// CHECK: 0 | struct X (base)
+// CHECK: 0 | (X vbtable pointer)
+// CHECK: 4 | char a
+// CHECK: 8 | struct U (base)
+// CHECK: 8 | char a
+// CHECK: 9 | struct W (base) (empty)
+// CHECK: 9 | char a
+// CHECK: 12 | struct V (virtual base) (empty)
+// CHECK: | [sizeof=12, align=4
+// CHECK: | nvsize=12, nvalign=4]
+// CHECK-X64: *** Dumping AST Record Layout
+// CHECK-X64: 0 | struct B
+// CHECK-X64: 0 | struct X (base)
+// CHECK-X64: 0 | (X vbtable pointer)
+// CHECK-X64: 8 | char a
+// CHECK-X64: 16 | struct U (base)
+// CHECK-X64: 16 | char a
+// CHECK-X64: 17 | struct W (base) (empty)
+// CHECK-X64: 17 | char a
+// CHECK-X64: 24 | struct V (virtual base) (empty)
+// CHECK-X64: | [sizeof=24, align=8
+// CHECK-X64: | nvsize=24, nvalign=8]
+
+struct C : X, V, W { char a; };
+
+// CHECK: *** Dumping AST Record Layout
+// CHECK: 0 | struct C
+// CHECK: 0 | struct X (base)
+// CHECK: 0 | (X vbtable pointer)
+// CHECK: 4 | char a
+// CHECK: 9 | struct V (base) (empty)
+// CHECK: 10 | struct W (base) (empty)
+// CHECK: 10 | char a
+// CHECK: 12 | struct V (virtual base) (empty)
+// CHECK: | [sizeof=12, align=4
+// CHECK: | nvsize=12, nvalign=4]
+// CHECK-X64: *** Dumping AST Record Layout
+// CHECK-X64: 0 | struct C
+// CHECK-X64: 0 | struct X (base)
+// CHECK-X64: 0 | (X vbtable pointer)
+// CHECK-X64: 8 | char a
+// CHECK-X64: 17 | struct V (base) (empty)
+// CHECK-X64: 18 | struct W (base) (empty)
+// CHECK-X64: 18 | char a
+// CHECK-X64: 24 | struct V (virtual base) (empty)
+// CHECK-X64: | [sizeof=24, align=8
+// CHECK-X64: | nvsize=24, nvalign=8]
+
+struct D : X, U, V, W { char a; };
+
+// CHECK: *** Dumping AST Record Layout
+// CHECK: 0 | struct D
+// CHECK: 0 | struct X (base)
+// CHECK: 0 | (X vbtable pointer)
+// CHECK: 4 | char a
+// CHECK: 8 | struct U (base)
+// CHECK: 8 | char a
+// CHECK: 9 | struct V (base) (empty)
+// CHECK: 10 | struct W (base) (empty)
+// CHECK: 10 | char a
+// CHECK: 12 | struct V (virtual base) (empty)
+// CHECK: | [sizeof=12, align=4
+// CHECK: | nvsize=12, nvalign=4]
+// CHECK-X64: *** Dumping AST Record Layout
+// CHECK-X64: 0 | struct D
+// CHECK-X64: 0 | struct X (base)
+// CHECK-X64: 0 | (X vbtable pointer)
+// CHECK-X64: 8 | char a
+// CHECK-X64: 16 | struct U (base)
+// CHECK-X64: 16 | char a
+// CHECK-X64: 17 | struct V (base) (empty)
+// CHECK-X64: 18 | struct W (base) (empty)
+// CHECK-X64: 18 | char a
+// CHECK-X64: 24 | struct V (virtual base) (empty)
+// CHECK-X64: | [sizeof=24, align=8
+// CHECK-X64: | nvsize=24, nvalign=8]
+
+struct E : X, U, Y, V, W { char a; };
+
+// CHECK: *** Dumping AST Record Layout
+// CHECK: 0 | struct E
+// CHECK: 0 | struct X (base)
+// CHECK: 0 | (X vbtable pointer)
+// CHECK: 4 | char a
+// CHECK: 8 | struct U (base)
+// CHECK: 8 | char a
+// CHECK: 12 | struct Y (base)
+// CHECK: 12 | (Y vbtable pointer)
+// CHECK: 16 | char a
+// CHECK: 21 | struct V (base) (empty)
+// CHECK: 22 | struct W (base) (empty)
+// CHECK: 22 | char a
+// CHECK: 24 | struct V (virtual base) (empty)
+// CHECK: | [sizeof=24, align=4
+// CHECK: | nvsize=24, nvalign=4]
+// CHECK-X64: *** Dumping AST Record Layout
+// CHECK-X64: 0 | struct E
+// CHECK-X64: 0 | struct X (base)
+// CHECK-X64: 0 | (X vbtable pointer)
+// CHECK-X64: 8 | char a
+// CHECK-X64: 16 | struct U (base)
+// CHECK-X64: 16 | char a
+// CHECK-X64: 24 | struct Y (base)
+// CHECK-X64: 24 | (Y vbtable pointer)
+// CHECK-X64: 32 | char a
+// CHECK-X64: 41 | struct V (base) (empty)
+// CHECK-X64: 42 | struct W (base) (empty)
+// CHECK-X64: 42 | char a
+// CHECK-X64: 48 | struct V (virtual base) (empty)
+// CHECK-X64: | [sizeof=48, align=8
+// CHECK-X64: | nvsize=48, nvalign=8]
+
+struct F : Z, W { char a; };
+
+// CHECK: *** Dumping AST Record Layout
+// CHECK: 0 | struct F
+// CHECK: 0 | struct Z (base)
+// CHECK: 0 | struct Y (base)
+// CHECK: 0 | (Y vbtable pointer)
+// CHECK: 4 | char a
+// CHECK: 9 | struct W (base) (empty)
+// CHECK: 9 | char a
+// CHECK: 12 | struct V (virtual base) (empty)
+// CHECK: | [sizeof=12, align=4
+// CHECK: | nvsize=12, nvalign=4]
+// CHECK-X64: *** Dumping AST Record Layout
+// CHECK-X64: 0 | struct F
+// CHECK-X64: 0 | struct Z (base)
+// CHECK-X64: 0 | struct Y (base)
+// CHECK-X64: 0 | (Y vbtable pointer)
+// CHECK-X64: 8 | char a
+// CHECK-X64: 17 | struct W (base) (empty)
+// CHECK-X64: 17 | char a
+// CHECK-X64: 24 | struct V (virtual base) (empty)
+// CHECK-X64: | [sizeof=24, align=8
+// CHECK-X64: | nvsize=24, nvalign=8]
+
+struct G : X, W, Y, V { char a; };
+
+// CHECK: *** Dumping AST Record Layout
+// CHECK: 0 | struct G
+// CHECK: 0 | struct X (base)
+// CHECK: 0 | (X vbtable pointer)
+// CHECK: 4 | char a
+// CHECK: 9 | struct W (base) (empty)
+// CHECK: 12 | struct Y (base)
+// CHECK: 12 | (Y vbtable pointer)
+// CHECK: 16 | char a
+// CHECK: 21 | struct V (base) (empty)
+// CHECK: 21 | char a
+// CHECK: 24 | struct V (virtual base) (empty)
+// CHECK: | [sizeof=24, align=4
+// CHECK: | nvsize=24, nvalign=4]
+// CHECK-X64: *** Dumping AST Record Layout
+// CHECK-X64: 0 | struct G
+// CHECK-X64: 0 | struct X (base)
+// CHECK-X64: 0 | (X vbtable pointer)
+// CHECK-X64: 8 | char a
+// CHECK-X64: 17 | struct W (base) (empty)
+// CHECK-X64: 24 | struct Y (base)
+// CHECK-X64: 24 | (Y vbtable pointer)
+// CHECK-X64: 32 | char a
+// CHECK-X64: 41 | struct V (base) (empty)
+// CHECK-X64: 41 | char a
+// CHECK-X64: 48 | struct V (virtual base) (empty)
+// CHECK-X64: | [sizeof=48, align=8
+// CHECK-X64: | nvsize=48, nvalign=8]
+
+int a[
+sizeof(A)+
+sizeof(B)+
+sizeof(C)+
+sizeof(D)+
+sizeof(E)+
+sizeof(F)+
+sizeof(G)];
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