clang/lib/AST/ODRHash.cpp

//===-- ODRHash.cpp - Hashing to diagnose ODR failures ----------*- C++ -*-===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
///
/// \file
/// This file implements the ODRHash class, which calculates a hash based
/// on AST nodes, which is stable across different runs.
///
//===----------------------------------------------------------------------===//

#include "clang/AST/ODRHash.h"

#include "clang/AST/DeclVisitor.h"
#include "clang/AST/NestedNameSpecifier.h"
#include "clang/AST/StmtVisitor.h"
#include "clang/AST/TypeVisitor.h"

using namespace clang;

void ODRHash::AddStmt(const Stmt *S) {}
void ODRHash::AddIdentifierInfo(const IdentifierInfo *II) {}
void ODRHash::AddNestedNameSpecifier(const NestedNameSpecifier *NNS) {}
void ODRHash::AddTemplateName(TemplateName Name) {}
void ODRHash::AddDeclarationName(DeclarationName Name) {}
void ODRHash::AddTemplateArgument(TemplateArgument TA) {}
void ODRHash::AddTemplateParameterList(const TemplateParameterList *TPL) {}

void ODRHash::clear() {
  DeclMap.clear();
  TypeMap.clear();
  Bools.clear();
  ID.clear();
}

unsigned ODRHash::CalculateHash() {
  // Append the bools to the end of the data segment backwards.  This allows
  // for the bools data to be compressed 32 times smaller compared to using
  // ID.AddBoolean
  const unsigned unsigned_bits = sizeof(unsigned) * CHAR_BIT;
  const unsigned size = Bools.size();
  const unsigned remainder = size % unsigned_bits;
  const unsigned loops = size / unsigned_bits;
  auto I = Bools.rbegin();
  unsigned value = 0;
  for (unsigned i = 0; i < remainder; ++i) {
    value <<= 1;
    value |= *I;
    ++I;
  }
  ID.AddInteger(value);

  for (unsigned i = 0; i < loops; ++i) {
    value = 0;
    for (unsigned j = 0; j < unsigned_bits; ++j) {
      value <<= 1;
      value |= *I;
      ++I;
    }
    ID.AddInteger(value);
  }

  assert(I == Bools.rend());
  Bools.clear();
  return ID.ComputeHash();
}

// Process a Decl pointer.  Add* methods call back into ODRHash while Visit*
// methods process the relevant parts of the Decl.
class ODRDeclVisitor : public ConstDeclVisitor<ODRDeclVisitor> {
  typedef ConstDeclVisitor<ODRDeclVisitor> Inherited;
  llvm::FoldingSetNodeID &ID;
  ODRHash &Hash;

public:
  ODRDeclVisitor(llvm::FoldingSetNodeID &ID, ODRHash &Hash)
      : ID(ID), Hash(Hash) {}

  void Visit(const Decl *D) {
    ID.AddInteger(D->getKind());
    Inherited::Visit(D);
  }

  void VisitAccessSpecDecl(const AccessSpecDecl *D) {
    ID.AddInteger(D->getAccess());
    Inherited::VisitAccessSpecDecl(D);
  }
};

// Only allow a small portion of Decl's to be processed.  Remove this once
// all Decl's can be handled.
bool ODRHash::isWhitelistedDecl(const Decl *D, const CXXRecordDecl *Parent) {
  if (D->isImplicit()) return false;
  if (D->getDeclContext() != Parent) return false;

  switch (D->getKind()) {
    default:
      return false;
    case Decl::AccessSpec:
      return true;
  }
}

void ODRHash::AddSubDecl(const Decl *D) {
  assert(D && "Expecting non-null pointer.");
  AddDecl(D);

  ODRDeclVisitor(ID, *this).Visit(D);
}

void ODRHash::AddCXXRecordDecl(const CXXRecordDecl *Record) {
  assert(Record && Record->hasDefinition() &&
         "Expected non-null record to be a definition.");
  AddDecl(Record);

  // Filter out sub-Decls which will not be processed in order to get an
  // accurate count of Decl's.
  llvm::SmallVector<const Decl *, 16> Decls;
  for (const Decl *SubDecl : Record->decls()) {
    if (isWhitelistedDecl(SubDecl, Record)) {
      Decls.push_back(SubDecl);
    }
  }

  ID.AddInteger(Decls.size());
  for (auto SubDecl : Decls) {
    AddSubDecl(SubDecl);
  }
}

void ODRHash::AddDecl(const Decl *D) {
  assert(D && "Expecting non-null pointer.");
  auto Result = DeclMap.insert(std::make_pair(D, DeclMap.size()));
  ID.AddInteger(Result.first->second);
  // On first encounter of a Decl pointer, process it.  Every time afterwards,
  // only the index value is needed.
  if (!Result.second) {
    return;
  }

  ID.AddInteger(D->getKind());
}

void ODRHash::AddType(const Type *T) {}
void ODRHash::AddQualType(QualType T) {}
void ODRHash::AddBoolean(bool Value) {
  Bools.push_back(Value);
}