CGBitFieldInfo CGBitFieldInfo::MakeInfo(CodeGenTypes &Types,
const FieldDecl *FD,
uint64_t Offset, uint64_t Size,
uint64_t StorageSize,
uint64_t StorageAlignment) {
llvm::Type *Ty = Types.ConvertTypeForMem(FD->getType());
CharUnits TypeSizeInBytes =
CharUnits::fromQuantity(Types.getDataLayout().getTypeAllocSize(Ty));
uint64_t TypeSizeInBits = Types.getContext().toBits(TypeSizeInBytes);
bool IsSigned = FD->getType()->isSignedIntegerOrEnumerationType();
if (Size > TypeSizeInBits) {
// We have a wide bit-field. The extra bits are only used for padding, so
// if we have a bitfield of type T, with size N:
//
// T t : N;
//
// We can just assume that it's:
//
// T t : sizeof(T);
//
Size = TypeSizeInBits;
}
// Reverse the bit offsets for big endian machines. Because we represent
// a bitfield as a single large integer load, we can imagine the bits
// counting from the most-significant-bit instead of the
// least-significant-bit.
if (Types.getDataLayout().isBigEndian()) {
Offset = StorageSize - (Offset + Size);
}
return CGBitFieldInfo(Offset, Size, IsSigned, StorageSize, StorageAlignment);
}
CGBitFieldInfo CGBitFieldInfo::MakeInfo(CodeGenTypes &Types,
const FieldDecl *FD,
uint64_t Offset, uint64_t Size,
uint64_t StorageSize,
CharUnits StorageOffset) {
// This function is vestigial from CGRecordLayoutBuilder days but is still
// used in GCObjCRuntime.cpp. That usage has a "fixme" attached to it that
// when addressed will allow for the removal of this function.
llvm::Type *Ty = Types.ConvertTypeForMem(FD->getType());
CharUnits TypeSizeInBytes =
CharUnits::fromQuantity(Types.getDataLayout().getTypeAllocSize(Ty));
uint64_t TypeSizeInBits = Types.getContext().toBits(TypeSizeInBytes);
bool IsSigned = FD->getType()->isSignedIntegerOrEnumerationType();
if (Size > TypeSizeInBits) {
// We have a wide bit-field. The extra bits are only used for padding, so
// if we have a bitfield of type T, with size N:
//
// T t : N;
//
// We can just assume that it's:
//
// T t : sizeof(T);
//
Size = TypeSizeInBits;
}
// Reverse the bit offsets for big endian machines. Because we represent
// a bitfield as a single large integer load, we can imagine the bits
// counting from the most-significant-bit instead of the
// least-significant-bit.
if (Types.getDataLayout().isBigEndian()) {
Offset = StorageSize - (Offset + Size);
}
return CGBitFieldInfo(Offset, Size, IsSigned, StorageSize, StorageOffset);
}
CGBitFieldInfo CGBitFieldInfo::MakeInfo(CodeGenTypes &Types,
const FieldDecl *FD,
uint64_t FieldOffset,
uint64_t FieldSize,
uint64_t ContainingTypeSizeInBits,
unsigned ContainingTypeAlign) {
llvm::Type *Ty = Types.ConvertTypeForMem(FD->getType());
CharUnits TypeSizeInBytes =
CharUnits::fromQuantity(Types.getTargetData().getTypeAllocSize(Ty));
uint64_t TypeSizeInBits = Types.getContext().toBits(TypeSizeInBytes);
bool IsSigned = FD->getType()->isSignedIntegerOrEnumerationType();
if (FieldSize > TypeSizeInBits) {
// We have a wide bit-field. The extra bits are only used for padding, so
// if we have a bitfield of type T, with size N:
//
// T t : N;
//
// We can just assume that it's:
//
// T t : sizeof(T);
//
FieldSize = TypeSizeInBits;
}
// in big-endian machines the first fields are in higher bit positions,
// so revert the offset. The byte offsets are reversed(back) later.
if (Types.getTargetData().isBigEndian()) {
FieldOffset = ((ContainingTypeSizeInBits)-FieldOffset-FieldSize);
}
// Compute the access components. The policy we use is to start by attempting
// to access using the width of the bit-field type itself and to always access
// at aligned indices of that type. If such an access would fail because it
// extends past the bound of the type, then we reduce size to the next smaller
// power of two and retry. The current algorithm assumes pow2 sized types,
// although this is easy to fix.
//
assert(llvm::isPowerOf2_32(TypeSizeInBits) && "Unexpected type size!");
CGBitFieldInfo::AccessInfo Components[3];
unsigned NumComponents = 0;
unsigned AccessedTargetBits = 0; // The number of target bits accessed.
unsigned AccessWidth = TypeSizeInBits; // The current access width to attempt.
// If requested, widen the initial bit-field access to be register sized. The
// theory is that this is most likely to allow multiple accesses into the same
// structure to be coalesced, and that the backend should be smart enough to
// narrow the store if no coalescing is ever done.
//
// The subsequent code will handle align these access to common boundaries and
// guaranteeing that we do not access past the end of the structure.
if (Types.getCodeGenOpts().UseRegisterSizedBitfieldAccess) {
if (AccessWidth < Types.getTarget().getRegisterWidth())
AccessWidth = Types.getTarget().getRegisterWidth();
}
// Round down from the field offset to find the first access position that is
// at an aligned offset of the initial access type.
uint64_t AccessStart = FieldOffset - (FieldOffset % AccessWidth);
// Adjust initial access size to fit within record.
while (AccessWidth > Types.getTarget().getCharWidth() &&
AccessStart + AccessWidth > ContainingTypeSizeInBits) {
AccessWidth >>= 1;
AccessStart = FieldOffset - (FieldOffset % AccessWidth);
}
while (AccessedTargetBits < FieldSize) {
// Check that we can access using a type of this size, without reading off
// the end of the structure. This can occur with packed structures and
// -fno-bitfield-type-align, for example.
if (AccessStart + AccessWidth > ContainingTypeSizeInBits) {
// If so, reduce access size to the next smaller power-of-two and retry.
AccessWidth >>= 1;
assert(AccessWidth >= Types.getTarget().getCharWidth()
&& "Cannot access under byte size!");
continue;
}
// Otherwise, add an access component.
// First, compute the bits inside this access which are part of the
// target. We are reading bits [AccessStart, AccessStart + AccessWidth); the
// intersection with [FieldOffset, FieldOffset + FieldSize) gives the bits
// in the target that we are reading.
assert(FieldOffset < AccessStart + AccessWidth && "Invalid access start!");
assert(AccessStart < FieldOffset + FieldSize && "Invalid access start!");
uint64_t AccessBitsInFieldStart = std::max(AccessStart, FieldOffset);
uint64_t AccessBitsInFieldSize =
std::min(AccessWidth + AccessStart,
FieldOffset + FieldSize) - AccessBitsInFieldStart;
assert(NumComponents < 3 && "Unexpected number of components!");
CGBitFieldInfo::AccessInfo &AI = Components[NumComponents++];
AI.FieldIndex = 0;
// FIXME: We still follow the old access pattern of only using the field
// byte offset. We should switch this once we fix the struct layout to be
// pretty.
// on big-endian machines we reverted the bit offset because first fields are
// in higher bits. But this also reverts the bytes, so fix this here by reverting
// the byte offset on big-endian machines.
if (Types.getTargetData().isBigEndian()) {
AI.FieldByteOffset = Types.getContext().toCharUnitsFromBits(
ContainingTypeSizeInBits - AccessStart - AccessWidth);
} else {
AI.FieldByteOffset = Types.getContext().toCharUnitsFromBits(AccessStart);
}
AI.FieldBitStart = AccessBitsInFieldStart - AccessStart;
AI.AccessWidth = AccessWidth;
AI.AccessAlignment = Types.getContext().toCharUnitsFromBits(
llvm::MinAlign(ContainingTypeAlign, AccessStart));
AI.TargetBitOffset = AccessedTargetBits;
AI.TargetBitWidth = AccessBitsInFieldSize;
AccessStart += AccessWidth;
AccessedTargetBits += AI.TargetBitWidth;
}