include/clang/AST/CFG.h

//===--- CFG.h - Classes for representing and building CFGs------*- C++ -*-===//
//
//                     The LLVM Compiler Infrastructure
//
// This file was developed by Ted Kremenek and is distributed under
// the University of Illinois Open Source License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
//  This file defines the CFG and CFGBuilder classes for representing and
//  building Control-Flow Graphs (CFGs) from ASTs.
//
//===----------------------------------------------------------------------===//

#ifndef LLVM_CLANG_CFG_H
#define LLVM_CLANG_CFG_H

#include "llvm/ADT/GraphTraits.h"
#include <list>
#include <vector>
#include <iosfwd>

namespace clang {

  class Stmt;
  class CFG;
  class PrinterHelper;
  
/// CFGBlock - Represents a single basic block in a source-level CFG.
///  It consists of:
///
///  (1) A set of statements/expressions (which may contain subexpressions).
///  (2) A "terminator" statement (not in the set of statements).
///  (3) A list of successors and predecessors.
///
/// Terminator: The terminator represents the type of control-flow that occurs
/// at the end of the basic block.  The terminator is a Stmt* referring to an
/// AST node that has control-flow: if-statements, breaks, loops, etc.
/// If the control-flow is conditional, the condition expression will appear
/// within the set of statements in the block (usually the last statement).
///
/// Predecessors: the order in the set of predecessors is arbitrary.
///
/// Successors: the order in the set of successors is NOT arbitrary.  We
///  currently have the following orderings based on the terminator:
///
///     Terminator       Successor Ordering
///  -----------------------------------------------------
///       if            Then Block;  Else Block
///     ? operator      LHS expression;  RHS expression
///     &&, ||          expression that uses result of && or ||, RHS
///
class CFGBlock {
  typedef std::vector<Stmt*> StatementListTy;
  /// Stmts - The set of statements in the basic block.
  StatementListTy Stmts;

  /// Label - An (optional) label that prefixes the executable
  ///  statements in the block.  When this variable is non-NULL, it is
  ///  either an instance of LabelStmt or SwitchCase.
  Stmt* Label;
  
  /// Terminator - The terminator for a basic block that
  ///  indicates the type of control-flow that occurs between a block
  ///  and its successors.
  Stmt* Terminator;
  
  /// BlockID - A numerical ID assigned to a CFGBlock during construction
  ///   of the CFG.
  unsigned BlockID;
  
  /// Predecessors/Successors - Keep track of the predecessor / successor
  /// CFG blocks.
  typedef std::vector<CFGBlock*> AdjacentBlocks;
  AdjacentBlocks Preds;
  AdjacentBlocks Succs;
  
public:
  explicit CFGBlock(unsigned blockid) : Label(NULL), Terminator(NULL),
                                        BlockID(blockid) {}
  ~CFGBlock() {};

  // Statement iterators
  typedef StatementListTy::iterator                                  iterator;
  typedef StatementListTy::const_iterator                      const_iterator;
  typedef std::reverse_iterator<const_iterator>        const_reverse_iterator;
  typedef std::reverse_iterator<iterator>                    reverse_iterator;
  
  Stmt*                        front()             { return Stmts.front();   }
  Stmt*                        back()              { return Stmts.back();    }
  
  iterator                     begin()             { return Stmts.begin();   }
  iterator                     end()               { return Stmts.end();     }
  const_iterator               begin()       const { return Stmts.begin();   }
  const_iterator               end()         const { return Stmts.end();     } 

  reverse_iterator             rbegin()            { return Stmts.rbegin();  }
  reverse_iterator             rend()              { return Stmts.rend();    }
  const_reverse_iterator       rbegin()      const { return Stmts.rbegin();  }
  const_reverse_iterator       rend()        const { return Stmts.rend();    }
  
  unsigned                     size()        const { return Stmts.size();    }
  bool                         empty()       const { return Stmts.empty();   }
    
  // CFG iterators
  typedef AdjacentBlocks::iterator                              pred_iterator;
  typedef AdjacentBlocks::const_iterator                  const_pred_iterator;
  typedef AdjacentBlocks::reverse_iterator              pred_reverse_iterator;
  typedef AdjacentBlocks::const_reverse_iterator  const_pred_reverse_iterator;

  typedef AdjacentBlocks::iterator                              succ_iterator;
  typedef AdjacentBlocks::const_iterator                  const_succ_iterator;
  typedef AdjacentBlocks::reverse_iterator              succ_reverse_iterator;
  typedef AdjacentBlocks::const_reverse_iterator  const_succ_reverse_iterator;
  
  pred_iterator                pred_begin()        { return Preds.begin();   }
  pred_iterator                pred_end()          { return Preds.end();     }
  const_pred_iterator          pred_begin()  const { return Preds.begin();   }
  const_pred_iterator          pred_end()    const { return Preds.end();     }
  
  pred_reverse_iterator        pred_rbegin()       { return Preds.rbegin();  }
  pred_reverse_iterator        pred_rend()         { return Preds.rend();    }  
  const_pred_reverse_iterator  pred_rbegin() const { return Preds.rbegin();  }
  const_pred_reverse_iterator  pred_rend()   const { return Preds.rend();    }

  succ_iterator                succ_begin()        { return Succs.begin();   }    
  succ_iterator                succ_end()          { return Succs.end();     }
  const_succ_iterator          succ_begin()  const { return Succs.begin();   }
  const_succ_iterator          succ_end()    const { return Succs.end();     }  
    
  succ_reverse_iterator        succ_rbegin()       { return Succs.rbegin();  }
  succ_reverse_iterator        succ_rend()         { return Succs.rend();    }
  const_succ_reverse_iterator  succ_rbegin() const { return Succs.rbegin();  }
  const_succ_reverse_iterator  succ_rend()   const { return Succs.rend();    }

  unsigned                     succ_size()   const { return Succs.size();    }
  bool                         succ_empty()  const { return Succs.empty();   }

  unsigned                     pred_size()   const { return Preds.size();    }
  bool                         pred_empty()  const { return Preds.empty();   }
  
  // Manipulation of block contents
  
  void appendStmt(Stmt* Statement) { Stmts.push_back(Statement); }
  void setTerminator(Stmt* Statement) { Terminator = Statement; }
  void setLabel(Stmt* Statement) { Label = Statement; }

  Stmt* getTerminator() { return Terminator; }
  const Stmt* getTerminator() const { return Terminator; }
  
  Stmt* getLabel() { return Label; }
  const Stmt* getLabel() const { return Label; }
  
  void reverseStmts();
  
  void addSuccessor(CFGBlock* Block) {
    Block->Preds.push_back(this);
    Succs.push_back(Block);
  }
  
  unsigned getBlockID() const { return BlockID; }
  
  void dump(const CFG* cfg) const;
  void print(std::ostream& OS, const CFG* cfg) const;
};
  

/// CFG - Represents a source-level, intra-procedural CFG that represents the
///  control-flow of a Stmt.  The Stmt can represent an entire function body,
///  or a single expression.  A CFG will always contain one empty block that
///  represents the Exit point of the CFG.  A CFG will also contain a designated
///  Entry block.  The CFG solely represents control-flow; it consists of
///  CFGBlocks which are simply containers of Stmt*'s in the AST the CFG
///  was constructed from.
class CFG {
public:
  //===--------------------------------------------------------------------===//
  // CFG Construction & Manipulation.
  //===--------------------------------------------------------------------===//

  /// buildCFG - Builds a CFG from an AST.  The responsibility to free the
  ///   constructed CFG belongs to the caller.  
  static CFG* buildCFG(Stmt* AST);  
  
  /// createBlock - Create a new block in the CFG.  The CFG owns the block;
  ///  the caller should not directly free it.
  CFGBlock* createBlock();
  
  /// setEntry - Set the entry block of the CFG.  This is typically used
  ///  only during CFG construction.  Most CFG clients expect that the
  ///  entry block has no predecessors and contains no statements.
  void setEntry(CFGBlock *B) { Entry = B; }
  
  /// setExit - Set the exit block of the CFG.  This is typically used
  ///  only during CFG construction.  Most CFG clients expect that the
  ///  exit block has no successors and contains no statements.
  void setIndirectGotoBlock(CFGBlock* B) { IndirectGotoBlock = B; }
  
  //===--------------------------------------------------------------------===//
  // Block Iterators
  //===--------------------------------------------------------------------===//

  typedef std::list<CFGBlock>                      CFGBlockListTy;
  
  typedef CFGBlockListTy::iterator                 iterator;
  typedef CFGBlockListTy::const_iterator           const_iterator;
  typedef std::reverse_iterator<iterator>          reverse_iterator;
  typedef std::reverse_iterator<const_iterator>    const_reverse_iterator;

  CFGBlock&                 front()                { return Blocks.front(); }
  CFGBlock&                 back()                 { return Blocks.back(); }
  
  iterator                  begin()                { return Blocks.begin(); }
  iterator                  end()                  { return Blocks.end(); }
  const_iterator            begin()       const    { return Blocks.begin(); }
  const_iterator            end()         const    { return Blocks.end(); } 
  
  reverse_iterator          rbegin()               { return Blocks.rbegin(); }
  reverse_iterator          rend()                 { return Blocks.rend(); }
  const_reverse_iterator    rbegin()      const    { return Blocks.rbegin(); }
  const_reverse_iterator    rend()        const    { return Blocks.rend(); }
  
  CFGBlock&                 getEntry()             { return *Entry; }
  const CFGBlock&           getEntry()    const    { return *Entry; }
  CFGBlock&                 getExit()              { return *Exit; }
  const CFGBlock&           getExit()     const    { return *Exit; }

  CFGBlock*        getIndirectGotoBlock() { return IndirectGotoBlock; }
  const CFGBlock*  getIndirectGotoBlock() const { return IndirectGotoBlock; }
  
  //===--------------------------------------------------------------------===//
  // CFG Edges (Source Block, Destination Block)
  //===--------------------------------------------------------------------===//

  class Edge {
    const CFGBlock* S;
    const CFGBlock* D;
  public:
    Edge(const CFGBlock* src, const CFGBlock* dst) : S(src), D(dst) {}
    Edge(const Edge& RHS) : S(RHS.S), D(RHS.D) {}
    
    Edge& operator=(const Edge& RHS) { S = RHS.S; D = RHS.D; return *this; }
    
    const CFGBlock* getSrc() const { return S; }
    const CFGBlock* getDst() const { return D; }
        
    bool operator==(const Edge& RHS) const { return S == RHS.S && D == RHS.D; }    
    bool operator!=(const Edge& RHS) const { return !(*this == RHS); }
  };
  
  //===--------------------------------------------------------------------===//
  // CFG Introspection.
  //===--------------------------------------------------------------------===//

  unsigned getNumBlockIDs() const { return NumBlockIDs; }

  //===--------------------------------------------------------------------===//
  // CFG Debugging: Pretty-Printing and Visualization.
  //===--------------------------------------------------------------------===//

  void viewCFG() const;
  void print(std::ostream& OS) const;
  void dump() const;

  //===--------------------------------------------------------------------===//
  // Static Predicates pertaining to CFG-related properties.
  //===--------------------------------------------------------------------===//
  
  /// hasImplicitControlFlow - Returns true if a given expression is
  ///  is represented within a CFG as having a designated "statement slot"
  ///  within a CFGBlock to represent the execution of that expression.  This
  ///  is usefull for expressions that contain implicit control flow, such
  ///  as &&, ||, and ? operators, as well as commas and statement expressions.
  ///
  ///  For example, considering a CFGBlock with the following statement:
  ///  
  ///    (1) x = ... ? ... ? ...
  ///  
  ///  When the CFG is built, this logically becomes:
  ///  
  ///    (1) ... ? ... : ...  (a unique statement	slot for the ternary ?)
  ///    (2) x	= [E1]        (where E1 is	actually the ConditionalOperator*)
  ///  
  ///  A client of the CFG, when walking the statement at (2), will encounter
  ///  E1.  In	this case, hasImplicitControlFlow(E1) == true, and the client
  ///  will know that the expression E1 is explicitly placed into its own 
  ///  statement slot to	capture	the implicit control-flow it has.
  ///  
  ///  Special cases:
  ///
  ///  (1) Function calls.
  ///  Function calls are placed in their own statement slot so that
  ///  that we have a clear identification of "call-return" sites.  If
  ///  you see a CallExpr nested as a subexpression of E, the CallExpr appears
  ///  in a statement slot in the CFG that dominates the location of E.
  ///
  ///  (2) DeclStmts
  ///  We include DeclStmts because the initializer expressions for Decls
  ///  will be separated out into distinct statements in the CFG.  These
  ///  statements will dominate the Decl.
  ///
  static bool hasImplicitControlFlow(const Stmt* S);  

  //===--------------------------------------------------------------------===//
  // Internal: constructors and data.
  //===--------------------------------------------------------------------===//

  CFG() : Entry(NULL), Exit(NULL), IndirectGotoBlock(NULL), NumBlockIDs(0) {};
  ~CFG() {};
    
private:
  CFGBlock* Entry;
  CFGBlock* Exit;
  CFGBlock* IndirectGotoBlock;  // Special block to contain collective dispatch
  // for indirect gotos
  CFGBlockListTy Blocks;
  unsigned NumBlockIDs;
};
} // end namespace clang

//===----------------------------------------------------------------------===//
// GraphTraits specializations for CFG basic block graphs (source-level CFGs)
//===----------------------------------------------------------------------===//

namespace llvm {

// Traits for: CFGBlock

template <> struct GraphTraits<clang::CFGBlock* > {
  typedef clang::CFGBlock NodeType;
  typedef clang::CFGBlock::succ_iterator ChildIteratorType;
  
  static NodeType* getEntryNode(clang::CFGBlock* BB)
  { return BB; }

  static inline ChildIteratorType child_begin(NodeType* N)
  { return N->succ_begin(); }
    
  static inline ChildIteratorType child_end(NodeType* N)
  { return N->succ_end(); }
};

template <> struct GraphTraits<const clang::CFGBlock* > {
  typedef const clang::CFGBlock NodeType;
  typedef clang::CFGBlock::const_succ_iterator ChildIteratorType;
  
  static NodeType* getEntryNode(const clang::CFGBlock* BB)
  { return BB; }
  
  static inline ChildIteratorType child_begin(NodeType* N)
  { return N->succ_begin(); }
  
  static inline ChildIteratorType child_end(NodeType* N)
  { return N->succ_end(); }
};

template <> struct GraphTraits<Inverse<const clang::CFGBlock*> > {
  typedef const clang::CFGBlock NodeType;
  typedef clang::CFGBlock::const_pred_iterator ChildIteratorType;

  static NodeType *getEntryNode(Inverse<const clang::CFGBlock*> G)
  { return G.Graph; }

  static inline ChildIteratorType child_begin(NodeType* N)
  { return N->pred_begin(); }
  
  static inline ChildIteratorType child_end(NodeType* N)
  { return N->pred_end(); }
};

// Traits for: CFG

template <> struct GraphTraits<clang::CFG* > 
            : public GraphTraits<clang::CFGBlock* >  {

  typedef clang::CFG::iterator nodes_iterator;
  
  static NodeType *getEntryNode(clang::CFG* F) { return &F->getEntry(); }  
  static nodes_iterator nodes_begin(clang::CFG* F) { return F->begin(); }
  static nodes_iterator nodes_end(clang::CFG* F) { return F->end(); }
};

template <> struct GraphTraits< const clang::CFG* > 
            : public GraphTraits< const clang::CFGBlock* >  {

  typedef clang::CFG::const_iterator nodes_iterator;            

  static NodeType *getEntryNode( const clang::CFG* F) { return &F->getEntry(); }
  static nodes_iterator nodes_begin( const clang::CFG* F) { return F->begin(); }
  static nodes_iterator nodes_end( const clang::CFG* F) { return F->end(); }
};

template <> struct GraphTraits<Inverse<const clang::CFG*> >
            : public GraphTraits<Inverse<const clang::CFGBlock*> > {

  typedef clang::CFG::const_iterator nodes_iterator;

  static NodeType *getEntryNode(const clang::CFG* F) { return &F->getExit(); }
  static nodes_iterator nodes_begin(const clang::CFG* F) { return F->begin();}
  static nodes_iterator nodes_end(const clang::CFG* F) { return F->end(); }
};
  
} // end llvm namespace

#endif