clang/lib/AST/RecordLayoutBuilder.cpp - toolchain/llvm-project - Gitiles

 //=== 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/DeclCXX.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::LayoutNonVirtualBases(const CXXRecordDecl *RD) {
   assert(!RD->isPolymorphic() &&
          "FIXME: We don't support polymorphic classes yet!");

   for (CXXRecordDecl::base_class_const_iterator i = RD->bases_begin(),
        e = RD->bases_end(); i != e; ++i) {
     if (!i->isVirtual()) {
       const CXXRecordDecl *Base =
         cast<CXXRecordDecl>(i->getType()->getAsRecordType()->getDecl());
       LayoutNonVirtualBase(Base);
     }
   }
 }

 void ASTRecordLayoutBuilder::LayoutNonVirtualBase(const CXXRecordDecl *RD) {
   const ASTRecordLayout &BaseInfo = Ctx.getASTRecordLayout(RD);
     assert(BaseInfo.getDataSize() > 0 &&
            "FIXME: Handle empty classes.");

   // FIXME: Should get the non-virtual alignment of the base.
   unsigned BaseAlign = BaseInfo.getAlignment();

   // FIXME: Should get the non-virtual size of the base.
   uint64_t BaseSize = BaseInfo.getDataSize();

   // Round up the current record size to the base's alignment boundary.
   Size = (Size + (BaseAlign-1)) & ~(BaseAlign-1);

   // Non-virtual base class has offset too.
   FieldOffsets.push_back(Size);

   // Reserve space for this base.
   Size += BaseSize;

   // Remember the next available offset.
   NextOffset = Size;

   // Remember max struct/class alignment.
   UpdateAlignment(BaseAlign);
 }

 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());

   // If this is a C++ class, lay out the nonvirtual bases.
   if (Ctx.getLangOptions().CPlusPlus)
     LayoutNonVirtualBases(cast<CXXRecordDecl>(D));

   LayoutFields(D);

   // 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.getDataSize(), 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::LayoutFields(const RecordDecl *D) {
   // 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);
 }

 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);

   bool IsPODForThePurposeOfLayout;
   if (!Ctx.getLangOptions().CPlusPlus) {
     // In C, all record types are POD.
     IsPODForThePurposeOfLayout = true;
   } else {
     // FIXME: This is not always correct. See the part about bitfields at
     // http://www.codesourcery.com/public/cxx-abi/abi.html#POD for more info.
     IsPODForThePurposeOfLayout = cast<CXXRecordDecl>(D)->isPOD();
   }

   uint64_t DataSize =
     IsPODForThePurposeOfLayout ? Builder.Size : Builder.NextOffset;

   return new ASTRecordLayout(Builder.Size, Builder.Alignment, DataSize,
                              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());
 }
	//=== 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/DeclCXX.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::LayoutNonVirtualBases(const CXXRecordDecl *RD) {
	assert(!RD->isPolymorphic() &&
	"FIXME: We don't support polymorphic classes yet!");

	for (CXXRecordDecl::base_class_const_iterator i = RD->bases_begin(),
	e = RD->bases_end(); i != e; ++i) {
	if (!i->isVirtual()) {
	const CXXRecordDecl *Base =
	cast<CXXRecordDecl>(i->getType()->getAsRecordType()->getDecl());
	LayoutNonVirtualBase(Base);
	}
	}
	}

	void ASTRecordLayoutBuilder::LayoutNonVirtualBase(const CXXRecordDecl *RD) {
	const ASTRecordLayout &BaseInfo = Ctx.getASTRecordLayout(RD);
	assert(BaseInfo.getDataSize() > 0 &&
	"FIXME: Handle empty classes.");

	// FIXME: Should get the non-virtual alignment of the base.
	unsigned BaseAlign = BaseInfo.getAlignment();

	// FIXME: Should get the non-virtual size of the base.
	uint64_t BaseSize = BaseInfo.getDataSize();

	// Round up the current record size to the base's alignment boundary.
	Size = (Size + (BaseAlign-1)) & ~(BaseAlign-1);

	// Non-virtual base class has offset too.
	FieldOffsets.push_back(Size);

	// Reserve space for this base.
	Size += BaseSize;

	// Remember the next available offset.
	NextOffset = Size;

	// Remember max struct/class alignment.
	UpdateAlignment(BaseAlign);
	}

	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());

	// If this is a C++ class, lay out the nonvirtual bases.
	if (Ctx.getLangOptions().CPlusPlus)
	LayoutNonVirtualBases(cast<CXXRecordDecl>(D));

	LayoutFields(D);

	// 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.getDataSize(), 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::LayoutFields(const RecordDecl *D) {
	// 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);
	}

	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);

	bool IsPODForThePurposeOfLayout;
	if (!Ctx.getLangOptions().CPlusPlus) {
	// In C, all record types are POD.
	IsPODForThePurposeOfLayout = true;
	} else {
	// FIXME: This is not always correct. See the part about bitfields at
	// http://www.codesourcery.com/public/cxx-abi/abi.html#POD for more info.
	IsPODForThePurposeOfLayout = cast<CXXRecordDecl>(D)->isPOD();
	}

	uint64_t DataSize =
	IsPODForThePurposeOfLayout ? Builder.Size : Builder.NextOffset;

	return new ASTRecordLayout(Builder.Size, Builder.Alignment, DataSize,
	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());
	}