ConstantPropagationPass.hpp

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/* src/vm/jit/compiler2/ConstantPropagationPass.hpp - ConstantPropagationPass

   Copyright (C) 2013
   CACAOVM - Verein zur Foerderung der freien virtuellen Maschine CACAO

   This file is part of CACAO.

   This program is free software; you can redistribute it and/or
   modify it under the terms of the GNU General Public License as
   published by the Free Software Foundation; either version 2, or (at
   your option) any later version.

   This program is distributed in the hope that it will be useful, but
   WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program; if not, write to the Free Software
   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
   02110-1301, USA.

*/

#ifndef _JIT_COMPILER2_CONSTANTPROPAGATIONPASS
#define _JIT_COMPILER2_CONSTANTPROPAGATIONPASS

#include "vm/jit/compiler2/Pass.hpp"
#include "future/unordered_map.hpp"
#include "vm/jit/compiler2/Instructions.hpp"

#include <list>

namespace cacao {
namespace jit {
namespace compiler2 {

// forward declaration
class Instruction;

/**
 * ConstantPropagationPass
 *
 * This optimization pass is a combined version of constant folding (a.k.a
 * constant expression evaluation) and constant propagation, based on the
 * algorithm in @cite ReisingerBScThesis. Analysis and program transformations
 * in the course of this optimization are targeted at the high-level
 * intermediate representation of the compiler2. It evalutes operations at
 * compile-time, whose operands are all constants and propagates the results
 * of these evaluations as far as possible through the program.
 */
class ConstantPropagationPass : public Pass {
private:
    typedef unordered_map<Instruction*,bool> InstBoolMapTy;
    typedef unordered_map<Instruction*,std::size_t> InstIntMapTy;
    typedef std::list<Instruction*> WorkListTy;

    /**
     * This work list is used by the algorithm to store the instructions which
     * have to be reconsidered. at the beginning it therefore contains all
     * instructions.
     */
    WorkListTy workList;
    
    /**
     * will be used to look up whether an instruction is currently contained in the
     * worklist to avoid inserting an instruction which is already in the list
     */
    InstBoolMapTy inWorkList;
    
    /**
     * used to track for each instruction the number of its operands which are
     * already known to be constant
     */
    InstIntMapTy constantOperands;

    void replace_by_constant(Instruction *isnt, CONSTInst *c, Method *M);
    void propagate(Instruction *inst);

public:
    static char ID;
    ConstantPropagationPass() : Pass() {}
    virtual bool run(JITData &JD);
    virtual PassUsage& get_PassUsage(PassUsage &PA) const;
};

} // end namespace compiler2
} // end namespace jit
} // end namespace cacao

#endif /* _JIT_COMPILER2_CONSTANTPROPAGATIONPASS */


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