/*
 *  This file is part of the Jikes RVM project (http://jikesrvm.org).
 *
 *  This file is licensed to You under the Eclipse Public License (EPL);
 *  You may not use this file except in compliance with the License. You
 *  may obtain a copy of the License at
 *
 *      http://www.opensource.org/licenses/eclipse-1.0.php
 *
 *  See the COPYRIGHT.txt file distributed with this work for information
 *  regarding copyright ownership.
 */
package org.jikesrvm.compilers.opt.ssa;

import java.util.Enumeration;
import org.jikesrvm.compilers.opt.ir.Binary;
import org.jikesrvm.compilers.opt.ir.IR;
import org.jikesrvm.compilers.opt.ir.Instruction;
import org.jikesrvm.compilers.opt.ir.operand.Operand;

import static org.jikesrvm.compilers.opt.ir.Operators.INT_ADD;
import static org.jikesrvm.compilers.opt.ir.Operators.INT_SUB;
import static org.jikesrvm.compilers.opt.ir.Operators.LONG_ADD;
import static org.jikesrvm.compilers.opt.ir.Operators.LONG_SUB;
import static org.jikesrvm.compilers.opt.ir.Operators.REF_ADD;
import static org.jikesrvm.compilers.opt.ir.Operators.REF_SUB;

/**
 * This class implements index equivalence via global value numbering
 * and 'uniformly generated expressions'.  See EURO-PAR 01 paper for
 * more details.
 */
class UniformlyGeneratedGVN {
  static final boolean DEBUG = false;

  /**
   * Compute Index Equivalence with uniformly generated global value
   * numbers.
   *
   * <p> PRECONDITIONS: SSA form, register lists computed, SSA bit
   * computed.
   *
   * <p> POSTCONDITION: ir.HIRInfo.uniformlyGeneratedValueNumbers
   * holds results of the analysis. Does not modify the IR in any other way.
   *
   * @param ir the governing IR
   */
  public static void perform(IR ir) {

    // create 'standard' global value numbers.
    GlobalValueNumberState gvn = null;
    gvn = new GlobalValueNumberState(ir);

    // Merge classes related by a constant
    for (Enumeration<Instruction> e = ir.forwardInstrEnumerator(); e.hasMoreElements();) {
      Instruction s = e.nextElement();
      // Check if s is a fixed-point add/subtract instruction with
      // a constant second operand
      if (s.operator == INT_ADD ||
          s.operator == LONG_ADD ||
          s.operator == REF_ADD ||
          s.operator == REF_SUB ||
          s.operator == INT_SUB ||
          s.operator == LONG_SUB) {
        Operand val2 = Binary.getVal2(s);
        if (val2.isConstant()) {
          Operand lhs = Binary.getResult(s);
          Operand rhs = Binary.getVal1(s);
          gvn.mergeClasses(gvn.valueGraph.getVertex(lhs), gvn.valueGraph.getVertex(rhs));
        }
      }
    }

    if (DEBUG) {
      System.out.println("@@@@ START OF INDEX EQUIVALENCE VALUE NUMBERS FOR " + ir.method + " @@@@");
      gvn.printValueNumbers();
      System.out.println("@@@@ END OF INDEX EQUIVALENCE VALUE NUMBERS FOR " + ir.method + " @@@@");
    }

    ir.HIRInfo.uniformlyGeneratedValueNumbers = gvn;
  }
}