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Debug info: Support DWARF4 bitfields via DW_AT_data_bit_offset.
The DWARF2 specification of DW_AT_bit_offset was written from the perspective of a big-endian machine with unclear semantics for other systems. DWARF4 deprecated DW_AT_bit_offset and introduced a new attribute DW_AT_data_bit_offset that simply counts the number of bits from the beginning of the containing entity regardless of endianness. After this patch LLVM emits DW_AT_bit_offset for DWARF 2 or 3 and DW_AT_data_bit_offset when DWARF 4 or later is requested. llvm-svn: 267895
This commit is contained in:
Adrian Prantl
parent
7a46345c15
commit
ae61e8a345
@ -1395,41 +1395,43 @@ void DwarfUnit::constructMemberDIE(DIE &Buffer, const DIDerivedType *DT) {
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// Handle bitfield, assume bytes are 8 bits.
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addUInt(MemberDie, dwarf::DW_AT_byte_size, None, FieldSize/8);
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addUInt(MemberDie, dwarf::DW_AT_bit_size, None, Size);
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//
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// The DWARF 2 DW_AT_bit_offset is counting the bits between the most
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// significant bit of the aligned storage unit containing the bit field to
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// the most significan bit of the bit field.
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//
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// FIXME: DWARF 4 states that DW_AT_data_bit_offset (which
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// counts from the beginning, regardless of endianness) should
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// be used instead.
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//
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//
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// Struct Align Align Align
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// v v v v
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// +-----------+-----*-----+-----*-----+--
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// | ... |b1|b2|b3|b4|
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// +-----------+-----*-----+-----*-----+--
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// | | |<-- Size ->| |
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// |<---- Offset --->| |<--->|
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// | | | \_ DW_AT_bit_offset (little endian)
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// | |<--->|
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// |<--------->| \_ StartBitOffset = DW_AT_bit_offset (big endian)
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// \ = DW_AT_data_bit_offset (biendian)
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// \_ OffsetInBytes
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uint64_t Offset = DT->getOffsetInBits();
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uint64_t Align = DT->getAlignInBits() ? DT->getAlignInBits() : FieldSize;
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uint64_t AlignMask = ~(Align - 1);
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// The bits from the start of the storage unit to the start of the field.
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uint64_t StartBitOffset = Offset - (Offset & AlignMask);
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// The endian-dependent DWARF 2 offset.
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uint64_t DwarfBitOffset = Asm->getDataLayout().isLittleEndian()
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? OffsetToAlignment(Offset + Size, Align)
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: StartBitOffset;
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// The byte offset of the field's aligned storage unit inside the struct.
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OffsetInBytes = (Offset - StartBitOffset) / 8;
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addUInt(MemberDie, dwarf::DW_AT_bit_offset, None, DwarfBitOffset);
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if (DD->getDwarfVersion() >= 4)
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addUInt(MemberDie, dwarf::DW_AT_data_bit_offset, None, Offset);
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else {
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//
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// The DWARF 2 DW_AT_bit_offset is counting the bits between the most
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// significant bit of the aligned storage unit containing the bit field
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// to
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// the most significan bit of the bit field.
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//
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// Struct Align Align Align
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// v v v v
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// +-----------+-----*-----+-----*-----+--
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// | ... |b1|b2|b3|b4|
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// +-----------+-----*-----+-----*-----+--
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// | | |<-- Size ->| |
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// |<---- Offset --->| |<--->|
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// | | | \_ DW_AT_bit_offset (little endian)
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// | |<--->|
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// |<--------->| \_ StartBitOffset = DW_AT_bit_offset (big endian)
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// \ = DW_AT_data_bit_offset (biendian)
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// \_ OffsetInBytes
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// The endian-dependent DWARF 2 offset.
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uint64_t DwarfBitOffset = Asm->getDataLayout().isLittleEndian()
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? OffsetToAlignment(Offset + Size, Align)
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: StartBitOffset;
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addUInt(MemberDie, dwarf::DW_AT_bit_offset, None, DwarfBitOffset);
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}
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} else
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// This is not a bitfield.
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OffsetInBytes = DT->getOffsetInBits() / 8;
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56
test/DebugInfo/ARM/big-endian-bitfield.ll
Normal file
56
test/DebugInfo/ARM/big-endian-bitfield.ll
Normal file
@ -0,0 +1,56 @@
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; RUN: llc -O0 -filetype=obj -mtriple=armeb-none-linux %s -o - \
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; RUN: | llvm-dwarfdump --debug-dump=info - | FileCheck %s
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; Generated from:
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; struct S {
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; int j:5;
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; int k:6;
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; int m:5;
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; int n:8;
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; } s;
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target datalayout = "E-m:e-p:32:32-i64:64-v128:64:128-n32-S64"
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%struct.S = type { i24 }
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@s = common global %struct.S zeroinitializer, align 4
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!llvm.dbg.cu = !{!0}
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!llvm.module.flags = !{!12, !13, !14}
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!llvm.ident = !{!15}
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!0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "clang version 3.9.0 (trunk 267633)", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, enums: !2, globals: !3)
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!1 = !DIFile(filename: "bitfield.c", directory: "/Volumes/Data/llvm")
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!2 = !{}
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!3 = !{!4}
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!4 = distinct !DIGlobalVariable(name: "s", scope: !0, file: !1, line: 6, type: !5, isLocal: false, isDefinition: true, variable: %struct.S* @s)
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!5 = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "S", file: !1, line: 1, size: 32, align: 32, elements: !6)
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!6 = !{!7, !9, !10, !11}
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; CHECK: DW_TAG_member
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; CHECK-NEXT: DW_AT_name{{.*}}"j"
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; CHECK-NOT: DW_TAG
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; CHECK: DW_AT_data_bit_offset [DW_FORM_data1] (0x00)
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; CHECK: DW_AT_data_member_location [DW_FORM_data1] (0x00)
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!7 = !DIDerivedType(tag: DW_TAG_member, name: "j", scope: !5, file: !1, line: 2, baseType: !8, size: 5, align: 32)
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!8 = !DIBasicType(name: "int", size: 32, align: 32, encoding: DW_ATE_signed)
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; CHECK: DW_TAG_member
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; CHECK-NEXT: DW_AT_name{{.*}}"k"
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; CHECK-NOT: DW_TAG
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; CHECK: DW_AT_data_bit_offset [DW_FORM_data1] (0x05)
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; CHECK: DW_AT_data_member_location [DW_FORM_data1] (0x00)
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!9 = !DIDerivedType(tag: DW_TAG_member, name: "k", scope: !5, file: !1, line: 3, baseType: !8, size: 6, align: 32, offset: 5)
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; CHECK: DW_TAG_member
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; CHECK-NEXT: DW_AT_name{{.*}}"m"
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; CHECK-NOT: DW_TAG
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; CHECK: DW_AT_data_bit_offset [DW_FORM_data1] (0x0b)
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; CHECK: DW_AT_data_member_location [DW_FORM_data1] (0x00)
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!10 = !DIDerivedType(tag: DW_TAG_member, name: "m", scope: !5, file: !1, line: 4, baseType: !8, size: 5, align: 32, offset: 11)
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; CHECK: DW_TAG_member
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; CHECK-NEXT: DW_AT_name{{.*}}"n"
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; CHECK-NOT: DW_TAG
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; CHECK: DW_AT_data_bit_offset [DW_FORM_data1] (0x10)
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; CHECK: DW_AT_data_member_location [DW_FORM_data1] (0x00)
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!11 = !DIDerivedType(tag: DW_TAG_member, name: "n", scope: !5, file: !1, line: 5, baseType: !8, size: 8, align: 32, offset: 16)
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!12 = !{i32 2, !"Dwarf Version", i32 4}
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!13 = !{i32 2, !"Debug Info Version", i32 3}
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!14 = !{i32 1, !"PIC Level", i32 2}
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!15 = !{!"clang version 3.9.0 (trunk 267633)"}
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68
test/DebugInfo/X86/bitfields-dwarf4.ll
Normal file
68
test/DebugInfo/X86/bitfields-dwarf4.ll
Normal file
@ -0,0 +1,68 @@
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; RUN: llc -mtriple x86_64-apple-macosx -O0 -filetype=obj -o - %s \
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; RUN: | llvm-dwarfdump -debug-dump=info - | FileCheck %s
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;
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; Generated from:
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; #include <stdint.h>
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; #pragma pack(1)
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; struct PackedBits
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; {
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; char a;
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; uint32_t b : 5,
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; c : 27
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; } s;
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; #pragma pack()
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source_filename = "bitfield.c"
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target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"
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target triple = "x86_64-apple-macosx"
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%struct.PackedBits = type <{ i8, i32 }>
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@s = common global %struct.PackedBits zeroinitializer, align 1
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!llvm.dbg.cu = !{!0}
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!llvm.module.flags = !{!14, !15, !16}
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!llvm.ident = !{!17}
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!0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "clang version 3.9.0 (trunk 267633)", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, enums: !2, globals: !3)
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!1 = !DIFile(filename: "bitfield.c", directory: "/Volumes/Data/llvm")
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!2 = !{}
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!3 = !{!4}
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!4 = distinct !DIGlobalVariable(name: "s", scope: !0, file: !1, line: 8, type: !5, isLocal: false, isDefinition: true, variable: %struct.PackedBits* @s)
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!5 = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "PackedBits", file: !1, line: 3, size: 40, align: 8, elements: !6)
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!6 = !{!7, !9, !13}
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; CHECK: DW_TAG_member
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; CHECK-NEXT: DW_AT_name{{.*}}"a"
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; CHECK-NOT: DW_TAG
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; CHECK-NOT: DW_AT_bit_offset
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; CHECK-NOT: DW_AT_data_bit_offset
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; CHECK: DW_AT_data_member_location [DW_FORM_data1] (0x00)
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!7 = !DIDerivedType(tag: DW_TAG_member, name: "a", scope: !5, file: !1, line: 5, baseType: !8, size: 8, align: 8)
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!8 = !DIBasicType(name: "char", size: 8, align: 8, encoding: DW_ATE_signed_char)
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; CHECK: DW_TAG_member
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; CHECK-NEXT: DW_AT_name{{.*}}"b"
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; CHECK-NOT: DW_TAG
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; CHECK-NOT: DW_AT_bit_offset
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; CHECK: DW_AT_data_bit_offset [DW_FORM_data1] (0x08)
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; CHECK-NEXT: DW_AT_data_member_location [DW_FORM_data1] (0x00)
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!9 = !DIDerivedType(tag: DW_TAG_member, name: "b", scope: !5, file: !1, line: 6, baseType: !10, size: 5, align: 32, offset: 8)
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!10 = !DIDerivedType(tag: DW_TAG_typedef, name: "uint32_t", file: !11, line: 183, baseType: !12)
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!11 = !DIFile(filename: "/Volumes/Data/llvm/_build.ninja.release/bin/../lib/clang/3.9.0/include/stdint.h", directory: "/Volumes/Data/llvm")
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!12 = !DIBasicType(name: "unsigned int", size: 32, align: 32, encoding: DW_ATE_unsigned)
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; CHECK: DW_TAG_member
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; CHECK-NEXT: DW_AT_name{{.*}}"c"
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; CHECK-NOT: DW_TAG
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; CHECK-NOT: DW_AT_bit_offset
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; CHECK: DW_AT_data_bit_offset [DW_FORM_data1] (0x0d)
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; CHECK-NEXT: DW_AT_data_member_location [DW_FORM_data1] (0x00)
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!13 = !DIDerivedType(tag: DW_TAG_member, name: "c", scope: !5, file: !1, line: 7, baseType: !10, size: 27, align: 32, offset: 13)
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!14 = !{i32 2, !"Dwarf Version", i32 4}
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!15 = !{i32 2, !"Debug Info Version", i32 3}
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!16 = !{i32 1, !"PIC Level", i32 2}
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!17 = !{!"clang version 3.9.0 (trunk 267633)"}
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