path: root/lib/AST/RecordLayoutBuilder.cpp

//=== 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/Basic/TargetInfo.h"
#include "llvm/Support/Format.h"
#include "llvm/ADT/SmallSet.h"
#include "llvm/Support/MathExtras.h"

using namespace clang;

ASTRecordLayoutBuilder::ASTRecordLayoutBuilder(ASTContext &Context)
  : Context(Context), Size(0), Alignment(8), Packed(false), 
  UnfilledBitsInLastByte(0), MaxFieldAlignment(0), DataSize(0), IsUnion(false),
  NonVirtualSize(0), NonVirtualAlignment(8), FirstNearlyEmptyVBase(0) { }

/// IsNearlyEmpty - Indicates when a class has a vtable pointer, but
/// no other data.
bool ASTRecordLayoutBuilder::IsNearlyEmpty(const CXXRecordDecl *RD) const {
  // FIXME: Audit the corners
  if (!RD->isDynamicClass())
    return false;
  const ASTRecordLayout &BaseInfo = Context.getASTRecordLayout(RD);
  if (BaseInfo.getNonVirtualSize() == Context.Target.getPointerWidth(0))
    return true;
  return false;
}

void ASTRecordLayoutBuilder::IdentifyPrimaryBases(const CXXRecordDecl *RD) {
  const ASTRecordLayout::PrimaryBaseInfo &BaseInfo =
    Context.getASTRecordLayout(RD).getPrimaryBaseInfo();

  // If the record has a primary base class that is virtual, add it to the set
  // of primary bases.
  if (BaseInfo.isVirtual())
    IndirectPrimaryBases.insert(BaseInfo.getBase());

  // Now traverse all bases and find primary bases for them.
  for (CXXRecordDecl::base_class_const_iterator i = RD->bases_begin(),
         e = RD->bases_end(); i != e; ++i) {
    assert(!i->getType()->isDependentType() &&
           "Cannot layout class with dependent bases.");
    const CXXRecordDecl *Base =
      cast<CXXRecordDecl>(i->getType()->getAs<RecordType>()->getDecl());

    // Only bases with virtual bases participate in computing the
    // indirect primary virtual base classes.
    if (Base->getNumVBases())
      IdentifyPrimaryBases(Base);
  }
}

void
ASTRecordLayoutBuilder::SelectPrimaryVBase(const CXXRecordDecl *RD) {
  for (CXXRecordDecl::base_class_const_iterator I = RD->bases_begin(),
         E = RD->bases_end(); I != E; ++I) {
    assert(!I->getType()->isDependentType() &&
           "Cannot layout class with dependent bases.");

    const CXXRecordDecl *Base =
      cast<CXXRecordDecl>(I->getType()->getAs<RecordType>()->getDecl());

    // Check if this is a nearly empty virtual base.
    if (I->isVirtual() && IsNearlyEmpty(Base)) {
      // If it's not an indirect primary base, then we've found our primary
      // base.
      if (!IndirectPrimaryBases.count(Base)) {
        PrimaryBase = ASTRecordLayout::PrimaryBaseInfo(Base,
                                                       /*IsVirtual=*/true);
        return;
      }

      // Is this the first nearly empty virtual base?
      if (!FirstNearlyEmptyVBase)
        FirstNearlyEmptyVBase = Base;
    }

    SelectPrimaryVBase(Base);
    if (PrimaryBase.getBase())
      return;
  }
}

/// DeterminePrimaryBase - Determine the primary base of the given class.
void ASTRecordLayoutBuilder::DeterminePrimaryBase(const CXXRecordDecl *RD) {
  // If the class isn't dynamic, it won't have a primary base.
  if (!RD->isDynamicClass())
    return;

  // Compute all the primary virtual bases for all of our direct and
  // indirect bases, and record all their primary virtual base classes.
  for (CXXRecordDecl::base_class_const_iterator i = RD->bases_begin(),
         e = RD->bases_end(); i != e; ++i) {
    assert(!i->getType()->isDependentType() &&
           "Cannot lay out class with dependent bases.");
    const CXXRecordDecl *Base =
      cast<CXXRecordDecl>(i->getType()->getAs<RecordType>()->getDecl());
    IdentifyPrimaryBases(Base);
  }

  // If the record has a dynamic base class, attempt to choose a primary base
  // class. It is the first (in direct base class order) non-virtual dynamic
  // base class, if one exists.
  for (CXXRecordDecl::base_class_const_iterator i = RD->bases_begin(),
         e = RD->bases_end(); i != e; ++i) {
    // Ignore virtual bases.
    if (i->isVirtual())
      continue;

    const CXXRecordDecl *Base =
      cast<CXXRecordDecl>(i->getType()->getAs<RecordType>()->getDecl());

    if (Base->isDy