path: root/lib/AST/RecordLayoutBuilder.cpp

//=== RecordLayoutBuilder.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 "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/Format.h"
#include "llvm/ADT/SmallSet.h"
#include "llvm/Support/MathExtras.h"
#include <map>

using namespace clang;

namespace {

/// EmptySubobjectMap - Keeps track of which empty subobjects exist at different
/// offsets while laying out a C++ class.
class EmptySubobjectMap {
  ASTContext &Context;
  
  /// Class - The class whose empty entries we're keeping track of.
  const CXXRecordDecl *Class;
  
  /// ComputeEmptySubobjectSizes - Compute the size of the largest base or 
  /// member subobject that is empty.
  void ComputeEmptySubobjectSizes();
  
public:
  /// This holds the size of the largest empty subobject (either a base
  /// or a member). Will be zero if the record being built doesn't contain 
  /// any empty classes.
  uint64_t SizeOfLargestEmptySubobject;
  
  EmptySubobjectMap(ASTContext &Context, const CXXRecordDecl *Class)
    : Context(Context), Class(Class), SizeOfLargestEmptySubobject(0) { }
                    
};

void EmptySubobjectMap::ComputeEmptySubobjectSizes() {
  // Check the bases.
  for (CXXRecordDecl::base_class_const_iterator I = Class->bases_begin(),
       E = Class->bases_end(); I != E; ++I) {
    const CXXRecordDecl *BaseDecl =
      cast<CXXRecordDecl>(I->getType()->getAs<RecordType>()->getDecl());

    uint64_t EmptySize = 0;
    const ASTRecordLayout &Layout = Context.getASTRecordLayout(BaseDecl);
    if (BaseDecl->isEmpty()) {
      // If the class decl is empty, get its size.
      EmptySize = Layout.getSize();
    } else {
      // Otherwise, we get the largest empty subobject for the decl.
      EmptySize = Layout.getSizeOfLargestEmptySubobject();
    }
    
    SizeOfLargestEmptySubobject = std::max(SizeOfLargestEmptySubobject, 
                                           EmptySize);
  }
  
  // Check the fields.
  for (CXXRecordDecl::field_iterator I = Class->field_begin(),
       E = Class->field_end(); I !=