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//=== ASTRecordLayoutBuilder.cpp - Helper class for building record layouts ==//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
#include "RecordLayoutBuilder.h"
#include "clang/AST/Attr.h"
#include "clang/AST/Decl.h"
#include "clang/AST/DeclObjC.h"
#include "clang/AST/Expr.h"
#include "clang/AST/RecordLayout.h"
#include "clang/Basic/TargetInfo.h"
#include <llvm/Support/MathExtras.h>
using namespace clang;
ASTRecordLayoutBuilder::ASTRecordLayoutBuilder(ASTContext &Ctx)
: Ctx(Ctx), Size(0), Alignment(8), StructPacking(0), NextOffset(0),
IsUnion(false) {}
void ASTRecordLayoutBuilder::Layout(const RecordDecl *D) {
IsUnion = D->isUnion();
if (const PackedAttr* PA = D->getAttr<PackedAttr>())
StructPacking = PA->getAlignment();
if (const AlignedAttr *AA = D->getAttr<AlignedAttr>())
UpdateAlignment(AA->getAlignment());
// Layout each field, for now, just sequentially, respecting alignment. In
// the future, this will need to be tweakable by targets.
for (RecordDecl::field_iterator Field = D->field_begin(),
FieldEnd = D->field_end(); Field != FieldEnd; ++Field)
LayoutField(*Field);
// Finally, round the size of the total struct up to the alignment of the
// struct itself.
FinishLayout();
}
void ASTRecordLayoutBuilder::Layout(const ObjCInterfaceDecl *D,
const ObjCImplementationDecl *Impl) {
if (ObjCInterfaceDecl *SD = D->getSuperClass()) {
const ASTRecordLayout &SL = Ctx.getASTObjCInterfaceLayout(SD);
UpdateAlignment(SL.getAlignment());
// We start laying out ivars not at the end of the superclass
// structure, but at the next byte following the last field.
Size = llvm::RoundUpToAlignment(SL.NextOffset, 8);
NextOffset = Size;
}
if (const PackedAttr *PA = D->getAttr<PackedAttr>())
StructPacking = PA->getAlignment();
if (const AlignedAttr *AA = D->getAttr<AlignedAttr>())
UpdateAlignment(AA->getAlignment());
// Layout each ivar sequentially.
llvm::SmallVector<ObjCIvarDecl*, 16> Ivars;
Ctx.ShallowCollectObjCIvars(D, Ivars, Impl);
for (unsigned i = 0, e = Ivars.size(); i != e; ++i)
LayoutField(Ivars[i]);
// Finally, round the size of the total struct up to the alignment of the
// struct itself.
FinishLayout();
}
void ASTRecordLayoutBuilder::LayoutField(const FieldDecl *D) {
unsigned FieldPacking = StructPacking;
uint64_t FieldOffset = IsUnion ? 0 : Size;
uint64_t FieldSize;
unsigned FieldAlign;
// FIXME: Should this override struct packing? Probably we want to
// take the minimum?
if (const PackedAttr *PA = D->getAttr<PackedAttr>())
FieldPacking = PA->getAlignment();
if (const Expr *BitWidthExpr = D->getBitWidth()) {
// TODO: Need to check this algorithm on other targets!
// (tested on Linux-X86)
FieldSize = BitWidthExpr->EvaluateAsInt(Ctx).getZExtValue();
std::pair<uint64_t, unsigned> FieldInfo = Ctx.getTypeInfo(D->getType());
uint64_t TypeSize = FieldInfo.first;
// Determine the alignment of this bitfield. The packing
// attributes define a maximum and the alignment attribute defines
// a minimum.
// FIXME: What is the right behavior when the specified alignment
// is smaller than the specified packing?
FieldAlign = FieldInfo.second;
if (FieldPacking)
FieldAlign = std::min(FieldAlign, FieldPacking);
if (const AlignedAttr *AA = D->getAttr<AlignedAttr>())
FieldAlign = std::max(FieldAlign, AA->getAlignment());
// Check if we need to add padding to give the field the correct
// alignment.
if (FieldSize == 0 || (FieldOffset & (FieldAlign-1)) + FieldSize > TypeSize)
FieldOffset = (FieldOffset + (FieldAlign-1)) & ~(FieldAlign-1);
// Padding members don't affect overall alignment
if (!D->getIdentifier())
FieldAlign = 1;
} else {
if (D->getType()->isIncompleteArrayType()) {
// This is a flexible array member; we can't directly
// query getTypeInfo about these, so we figure it out here.
// Flexible array members don't have any size, but they
// have to be aligned appropriately for their element type.
FieldSize = 0;
const ArrayType* ATy = Ctx.getAsArrayType(D->getType());
FieldAlign = Ctx.getTypeAlign(ATy->getElementType());
} else if (const ReferenceType *RT = D->getType()->getAsReferenceType()) {
unsigned AS = RT->getPointeeType().getAddressSpace();
FieldSize = Ctx.Target.getPointerWidth(AS);
FieldAlign = Ctx.Target.getPointerAlign(AS);
} else {
std::pair<uint64_t, unsigned> FieldInfo = Ctx.getTypeInfo(D->getType());
FieldSize = FieldInfo.first;
FieldAlign = FieldInfo.second;
}
// Determine the alignment of this bitfield. The packing
// attributes define a maximum and the alignment attribute defines
// a minimum. Additionally, the packing alignment must be at least
// a byte for non-bitfields.
//
// FIXME: What is the right behavior when the specified alignment
// is smaller than the specified packing?
if (FieldPacking)
FieldAlign = std::min(FieldAlign, std::max(8U, FieldPacking));
if (const AlignedAttr *AA = D->getAttr<AlignedAttr>())
FieldAlign = std::max(FieldAlign, AA->getAlignment());
// Round up the current record size to the field's alignment boundary.
FieldOffset = (FieldOffset + (FieldAlign-1)) & ~(FieldAlign-1);
}
// Place this field at the current location.
FieldOffsets.push_back(FieldOffset);
// Reserve space for this field.
if (IsUnion)
Size = std::max(Size, FieldSize);
else
Size = FieldOffset + FieldSize;
// Remember the next available offset.
NextOffset = Size;
// Remember max struct/class alignment.
UpdateAlignment(FieldAlign);
}
void ASTRecordLayoutBuilder::FinishLayout() {
// In C++, records cannot be of size 0.
if (Ctx.getLangOptions().CPlusPlus && Size == 0)
Size = 8;
// Finally, round the size of the record up to the alignment of the
// record itself.
Size = (Size + (Alignment-1)) & ~(Alignment-1);
}
void ASTRecordLayoutBuilder::UpdateAlignment(unsigned NewAlignment) {
if (NewAlignment <= Alignment)
return;
assert(llvm::isPowerOf2_32(NewAlignment && "Alignment not a power of 2"));
Alignment = NewAlignment;
}
const ASTRecordLayout *
ASTRecordLayoutBuilder::ComputeLayout(ASTContext &Ctx,
const RecordDecl *D) {
ASTRecordLayoutBuilder Builder(Ctx);
Builder.Layout(D);
return new ASTRecordLayout(Builder.Size, Builder.Alignment,
Builder.NextOffset,
Builder.FieldOffsets.data(),
Builder.FieldOffsets.size());
}
const ASTRecordLayout *
ASTRecordLayoutBuilder::ComputeLayout(ASTContext &Ctx,
const ObjCInterfaceDecl *D,
const ObjCImplementationDecl *Impl) {
ASTRecordLayoutBuilder Builder(Ctx);
Builder.Layout(D, Impl);
return new ASTRecordLayout(Builder.Size, Builder.Alignment,
Builder.NextOffset,
Builder.FieldOffsets.data(),
Builder.FieldOffsets.size());
}
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