r218661 - MS ABI: Correct layout for empty records
David Majnemer
david.majnemer at gmail.com
Mon Sep 29 23:45:43 PDT 2014
Author: majnemer
Date: Tue Sep 30 01:45:43 2014
New Revision: 218661
URL: http://llvm.org/viewvc/llvm-project?rev=218661&view=rev
Log:
MS ABI: Correct layout for empty records
Empty records do not always have size equivalent to their alignment.
They only do so when their alignment is at least as large as the minimum
empty struct size: 1 byte in C++ and 4 bytes in C.
Modified:
cfe/trunk/lib/AST/RecordLayoutBuilder.cpp
cfe/trunk/test/Layout/ms-x86-basic-layout.cpp
cfe/trunk/test/Layout/ms-x86-pack-and-align.cpp
Modified: cfe/trunk/lib/AST/RecordLayoutBuilder.cpp
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/AST/RecordLayoutBuilder.cpp?rev=218661&r1=218660&r2=218661&view=diff
==============================================================================
--- cfe/trunk/lib/AST/RecordLayoutBuilder.cpp (original)
+++ cfe/trunk/lib/AST/RecordLayoutBuilder.cpp Tue Sep 30 01:45:43 2014
@@ -2204,6 +2204,8 @@ public:
CharUnits CurrentBitfieldSize;
/// \brief Offset to the virtual base table pointer (if one exists).
CharUnits VBPtrOffset;
+ /// \brief Minimum record size possible.
+ CharUnits MinEmptyStructSize;
/// \brief The size and alignment info of a pointer.
ElementInfo PointerInfo;
/// \brief The primary base class (if one exists).
@@ -2299,6 +2301,8 @@ MicrosoftRecordLayoutBuilder::getAdjuste
}
void MicrosoftRecordLayoutBuilder::layout(const RecordDecl *RD) {
+ // For C record layout, zero-sized records always have size 4.
+ MinEmptyStructSize = CharUnits::fromQuantity(4);
initializeLayout(RD);
layoutFields(RD);
DataSize = Size = Size.RoundUpToAlignment(Alignment);
@@ -2308,6 +2312,8 @@ void MicrosoftRecordLayoutBuilder::layou
}
void MicrosoftRecordLayoutBuilder::cxxLayout(const CXXRecordDecl *RD) {
+ // The C++ standard says that empty structs have size 1.
+ MinEmptyStructSize = CharUnits::One();
initializeLayout(RD);
initializeCXXLayout(RD);
layoutNonVirtualBases(RD);
@@ -2636,7 +2642,7 @@ void MicrosoftRecordLayoutBuilder::layou
void MicrosoftRecordLayoutBuilder::finalizeLayout(const RecordDecl *RD) {
// Respect required alignment. Note that in 32-bit mode Required alignment
- // may be 0 nad cause size not to be updated.
+ // may be 0 and cause size not to be updated.
DataSize = Size;
if (!RequiredAlignment.isZero()) {
Alignment = std::max(Alignment, RequiredAlignment);
@@ -2646,11 +2652,15 @@ void MicrosoftRecordLayoutBuilder::final
RoundingAlignment = std::max(RoundingAlignment, RequiredAlignment);
Size = Size.RoundUpToAlignment(RoundingAlignment);
}
- // Zero-sized structures have size equal to their alignment.
if (Size.isZero()) {
EndsWithZeroSizedObject = true;
LeadsWithZeroSizedBase = true;
- Size = Alignment;
+ // Zero-sized structures have size equal to their alignment if a
+ // __declspec(align) came into play.
+ if (RequiredAlignment >= MinEmptyStructSize)
+ Size = Alignment;
+ else
+ Size = MinEmptyStructSize;
}
}
Modified: cfe/trunk/test/Layout/ms-x86-basic-layout.cpp
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/Layout/ms-x86-basic-layout.cpp?rev=218661&r1=218660&r2=218661&view=diff
==============================================================================
--- cfe/trunk/test/Layout/ms-x86-basic-layout.cpp (original)
+++ cfe/trunk/test/Layout/ms-x86-basic-layout.cpp Tue Sep 30 01:45:43 2014
@@ -816,6 +816,36 @@ struct RecordArrayTypedef {
// CHECK-X64-NEXT: | [sizeof=16, align=4
// CHECK-X64-NEXT: | nvsize=16, nvalign=4]
+struct EmptyIntMemb {
+ int FlexArrayMemb[0];
+};
+
+// CHECK: *** Dumping AST Record Layout
+// CHECK-NEXT: 0 | struct EmptyIntMemb
+// CHECK-NEXT: 0 | int [0] FlexArrayMemb
+// CHECK-NEXT: | [sizeof=1, align=4
+// CHECK-NEXT: | nvsize=0, nvalign=4]
+// CHECK-X64: *** Dumping AST Record Layout
+// CHECK-X64-NEXT: 0 | struct EmptyIntMemb
+// CHECK-X64-NEXT: 0 | int [0] FlexArrayMemb
+// CHECK-X64-NEXT: | [sizeof=4, align=4
+// CHECK-X64-NEXT: | nvsize=0, nvalign=4]
+
+struct EmptyLongLongMemb {
+ long long FlexArrayMemb[0];
+};
+
+// CHECK: *** Dumping AST Record Layout
+// CHECK-NEXT: 0 | struct EmptyLongLongMemb
+// CHECK-NEXT: 0 | long long [0] FlexArrayMemb
+// CHECK-NEXT: | [sizeof=1, align=8
+// CHECK-NEXT: | nvsize=0, nvalign=8]
+// CHECK-X64: *** Dumping AST Record Layout
+// CHECK-X64-NEXT: 0 | struct EmptyLongLongMemb
+// CHECK-X64-NEXT: 0 | long long [0] FlexArrayMemb
+// CHECK-X64-NEXT: | [sizeof=8, align=8
+// CHECK-X64-NEXT: | nvsize=0, nvalign=8]
+
int a[
sizeof(TestF0)+
sizeof(TestF1)+
@@ -840,4 +870,6 @@ sizeof(F6)+
sizeof(ArrayFieldOfRecords)+
sizeof(ArrayOfArrayFieldOfRecords)+
sizeof(RecordArrayTypedef)+
+sizeof(EmptyIntMemb)+
+sizeof(EmptyLongLongMemb)+
0];
Modified: cfe/trunk/test/Layout/ms-x86-pack-and-align.cpp
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/Layout/ms-x86-pack-and-align.cpp?rev=218661&r1=218660&r2=218661&view=diff
==============================================================================
--- cfe/trunk/test/Layout/ms-x86-pack-and-align.cpp (original)
+++ cfe/trunk/test/Layout/ms-x86-pack-and-align.cpp Tue Sep 30 01:45:43 2014
@@ -769,6 +769,38 @@ struct QD {
// CHECK-X64-NEXT: | [sizeof=8, align=4
// CHECK-X64-NEXT: | nvsize=8, nvalign=4]
+struct __declspec(align(4)) EmptyAlignedLongLongMemb {
+ long long FlexArrayMemb[0];
+};
+
+// CHECK: *** Dumping AST Record Layout
+// CHECK-NEXT: 0 | struct EmptyAlignedLongLongMemb
+// CHECK-NEXT: 0 | long long [0] FlexArrayMemb
+// CHECK-NEXT: | [sizeof=8, align=8
+// CHECK-NEXT: | nvsize=0, nvalign=8]
+// CHECK-X64: *** Dumping AST Record Layout
+// CHECK-X64-NEXT: 0 | struct EmptyAlignedLongLongMemb
+// CHECK-X64-NEXT: 0 | long long [0] FlexArrayMemb
+// CHECK-X64-NEXT: | [sizeof=8, align=8
+// CHECK-X64-NEXT: | nvsize=0, nvalign=8]
+
+#pragma pack(1)
+struct __declspec(align(4)) EmptyPackedAlignedLongLongMemb {
+ long long FlexArrayMemb[0];
+};
+#pragma pack()
+
+// CHECK: *** Dumping AST Record Layout
+// CHECK-NEXT: 0 | struct EmptyPackedAlignedLongLongMemb
+// CHECK-NEXT: 0 | long long [0] FlexArrayMemb
+// CHECK-NEXT: | [sizeof=4, align=4
+// CHECK-NEXT: | nvsize=0, nvalign=4]
+// CHECK-X64: *** Dumping AST Record Layout
+// CHECK-X64-NEXT: 0 | struct EmptyPackedAlignedLongLongMemb
+// CHECK-X64-NEXT: 0 | long long [0] FlexArrayMemb
+// CHECK-X64-NEXT: | [sizeof=4, align=4
+// CHECK-X64-NEXT: | nvsize=0, nvalign=4]
+
int a[
sizeof(X)+
sizeof(Y)+
@@ -800,4 +832,6 @@ sizeof(PE)+
sizeof(QB)+
sizeof(QC)+
sizeof(QD)+
+sizeof(EmptyAlignedLongLongMemb)+
+sizeof(EmptyPackedAlignedLongLongMemb)+
0];
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