Structure with information about how a bitfield should be accessed. More...

#include "/home/buildbot/as-worker-4/publish-doxygen-docs/llvm-project/clang/lib/CodeGen/CGRecordLayout.h"

Public Member Functions
	CGBitFieldInfo ()

	CGBitFieldInfo (unsigned Offset, unsigned Size, bool IsSigned, unsigned StorageSize, CharUnits StorageOffset)

void	print (raw_ostream &OS) const

void	dump () const

Static Public Member Functions
static CGBitFieldInfo	MakeInfo (class CodeGenTypes &Types, const FieldDecl *FD, uint64_t Offset, uint64_t Size, uint64_t StorageSize, CharUnits StorageOffset)
	Given a bit-field decl, build an appropriate helper object for accessing that field (which is expected to have the given offset and size).

Public Attributes
unsigned	Offset: 16
	The offset within a contiguous run of bitfields that are represented as a single "field" within the LLVM struct type.

unsigned	Size: 15
	The total size of the bit-field, in bits.

unsigned	IsSigned: 1
	Whether the bit-field is signed.

unsigned	StorageSize
	The storage size in bits which should be used when accessing this bitfield.

CharUnits	StorageOffset
	The offset of the bitfield storage from the start of the struct.

unsigned	VolatileOffset: 16
	The offset within a contiguous run of bitfields that are represented as a single "field" within the LLVM struct type, taking into account the AAPCS rules for volatile bitfields.

unsigned	VolatileStorageSize
	The storage size in bits which should be used when accessing this bitfield.

CharUnits	VolatileStorageOffset
	The offset of the bitfield storage from the start of the struct.

Detailed Description

Structure with information about how a bitfield should be accessed.

Often we layout a sequence of bitfields as a contiguous sequence of bits. When the AST record layout does this, we represent it in the LLVM IR's type as either a sequence of i8 members or a byte array to reserve the number of bytes touched without forcing any particular alignment beyond the basic character alignment.

Then accessing a particular bitfield involves converting this byte array into a single integer of that size (i24 or i40 – may not be power-of-two size), loading it, and shifting and masking to extract the particular subsequence of bits which make up that particular bitfield. This structure encodes the information used to construct the extraction code sequences. The CGRecordLayout also has a field index which encodes which byte-sequence this bitfield falls within. Let's assume the following C struct:

struct S { char a, b, c; unsigned bits : 3; unsigned more_bits : 4; unsigned still_more_bits : 7; };

This will end up as the following LLVM type. The first array is the bitfield, and the second is the padding out to a 4-byte alignment.

t = type { i8, i8, i8, i8, i8, [3 x i8] }

When generating code to access more_bits, we'll generate something essentially like this:

define i32 @foo(t* base) { %0 = gep t* base, i32 0, i32 3 %2 = load i8* %1 %3 = lshr i8 %2, 3 %4 = and i8 %3, 15 %5 = zext i8 %4 to i32 ret i32 i }

Definition at line 65 of file CGRecordLayout.h.

Constructor & Destructor Documentation

◆ CGBitFieldInfo() [1/2]

clang::CodeGen::CGBitFieldInfo::CGBitFieldInfo ( )

inline

Definition at line 96 of file CGRecordLayout.h.

Referenced by MakeInfo().

◆ CGBitFieldInfo() [2/2]

clang::CodeGen::CGBitFieldInfo::CGBitFieldInfo	(	unsigned	Offset,
		unsigned	Size,
		bool	IsSigned,
		unsigned	StorageSize,
		CharUnits	StorageOffset
	)

inline

Definition at line 100 of file CGRecordLayout.h.

Member Function Documentation

◆ dump()

LLVM_DUMP_METHOD void CGBitFieldInfo::dump ( ) const

Definition at line 1261 of file CGRecordLayoutBuilder.cpp.

References print().

◆ MakeInfo()

CGBitFieldInfo CGBitFieldInfo::MakeInfo	(	class CodeGenTypes &	Types,
		const FieldDecl *	FD,
		uint64_t	Offset,
		uint64_t	Size,
		uint64_t	StorageSize,
		CharUnits	StorageOffset
	)

static

Given a bit-field decl, build an appropriate helper object for accessing that field (which is expected to have the given offset and size).

Definition at line 1047 of file CGRecordLayoutBuilder.cpp.

References CGBitFieldInfo(), clang::CharUnits::fromQuantity(), clang::ValueDecl::getType(), IsSigned, clang::Type::isSignedIntegerOrEnumerationType(), Offset, Size, StorageOffset, and StorageSize.

Referenced by clang::CodeGen::CGObjCRuntime::EmitValueForIvarAtOffset().

◆ print()

void CGBitFieldInfo::print ( raw_ostream & OS ) const

Definition at line 1251 of file CGRecordLayoutBuilder.cpp.

References clang::CharUnits::getQuantity(), IsSigned, Offset, Size, StorageOffset, StorageSize, VolatileOffset, VolatileStorageOffset, and VolatileStorageSize.

Referenced by dump().

Member Data Documentation

◆ IsSigned

unsigned clang::CodeGen::CGBitFieldInfo::IsSigned

Whether the bit-field is signed.

Definition at line 75 of file CGRecordLayout.h.

Referenced by MakeInfo(), and print().

◆ Offset

unsigned clang::CodeGen::CGBitFieldInfo::Offset

The offset within a contiguous run of bitfields that are represented as a single "field" within the LLVM struct type.

This offset is in bits.

Definition at line 68 of file CGRecordLayout.h.

Referenced by clang::CodeGen::CodeGenTypes::ComputeRecordLayout(), MakeInfo(), print(), and setUsedBits().

◆ Size

unsigned clang::CodeGen::CGBitFieldInfo::Size

The total size of the bit-field, in bits.

Definition at line 71 of file CGRecordLayout.h.

Referenced by clang::CodeGen::CodeGenTypes::ComputeRecordLayout(), MakeInfo(), print(), and setUsedBits().

◆ StorageOffset

CharUnits clang::CodeGen::CGBitFieldInfo::StorageOffset

The offset of the bitfield storage from the start of the struct.

Definition at line 82 of file CGRecordLayout.h.

Referenced by MakeInfo(), print(), and setUsedBits().

◆ StorageSize

unsigned clang::CodeGen::CGBitFieldInfo::StorageSize

The storage size in bits which should be used when accessing this bitfield.

Definition at line 79 of file CGRecordLayout.h.

Referenced by clang::CodeGen::CodeGenTypes::ComputeRecordLayout(), clang::CodeGen::CGObjCRuntime::EmitValueForIvarAtOffset(), MakeInfo(), print(), and setUsedBits().

◆ VolatileOffset

unsigned clang::CodeGen::CGBitFieldInfo::VolatileOffset

The offset within a contiguous run of bitfields that are represented as a single "field" within the LLVM struct type, taking into account the AAPCS rules for volatile bitfields.

This offset is in bits.

Definition at line 87 of file CGRecordLayout.h.

Referenced by print().

◆ VolatileStorageOffset

CharUnits clang::CodeGen::CGBitFieldInfo::VolatileStorageOffset

The offset of the bitfield storage from the start of the struct.

Definition at line 94 of file CGRecordLayout.h.