SplitBasicBlock.java

/*
 *  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.lir2mir;

import org.jikesrvm.compilers.opt.driver.CompilerPhase;
import org.jikesrvm.compilers.opt.ir.BasicBlock;
import org.jikesrvm.compilers.opt.ir.BasicBlockEnumeration;
import org.jikesrvm.compilers.opt.ir.IR;
import org.jikesrvm.compilers.opt.ir.Instruction;

/**
 * Splits a large basic block into smaller ones with size <=
 * OptOptions.L2M_MAX_BLOCK_SIZE
 */
public final class SplitBasicBlock extends CompilerPhase {

  public String getName() { return "SplitBasicBlock"; }

  public CompilerPhase newExecution(IR ir) { return this; }

  public void perform(IR ir) {
    for (BasicBlockEnumeration e = ir.getBasicBlocks(); e.hasMoreElements();) {
      BasicBlock bb = e.nextElement();

      if (!bb.isEmpty()) {
        while (bb != null) {
          bb = splitEachBlock(bb, ir);
        }
      }
    }
  }

  /**
   * Splits basic block
   *
   * @return null if no splitting is done, returns the second block if splitting is done.
   */
  BasicBlock splitEachBlock(BasicBlock bb, IR ir) {

    int instCount = ir.options.L2M_MAX_BLOCK_SIZE;
    for (Instruction inst = bb.firstInstruction(); inst != bb.lastInstruction(); inst =
        inst.nextInstructionInCodeOrder()) {
      if ((--instCount) <= 0) {
        if (inst.isBranch()) {
          return null; // no need to split because all the rests are just branches
        }
        // Now, split!
        return bb.splitNodeWithLinksAt(inst, ir);
      }
    }

    return null; // no splitting happened
  }

}