001/*
002 *  This file is part of the Jikes RVM project (http://jikesrvm.org).
003 *
004 *  This file is licensed to You under the Eclipse Public License (EPL);
005 *  You may not use this file except in compliance with the License. You
006 *  may obtain a copy of the License at
007 *
008 *      http://www.opensource.org/licenses/eclipse-1.0.php
009 *
010 *  See the COPYRIGHT.txt file distributed with this work for information
011 *  regarding copyright ownership.
012 */
013package org.jikesrvm.compilers.opt.controlflow;
014
015import static org.jikesrvm.compilers.opt.driver.OptConstants.INSTRUMENTATION_BCI;
016import static org.jikesrvm.compilers.opt.ir.Operators.IR_PROLOGUE_opcode;
017import static org.jikesrvm.compilers.opt.ir.Operators.YIELDPOINT_BACKEDGE;
018import static org.jikesrvm.compilers.opt.ir.Operators.YIELDPOINT_EPILOGUE;
019import static org.jikesrvm.compilers.opt.ir.Operators.YIELDPOINT_PROLOGUE;
020
021import java.util.Enumeration;
022
023import org.jikesrvm.VM;
024import org.jikesrvm.compilers.opt.driver.CompilerPhase;
025import org.jikesrvm.compilers.opt.inlining.InlineSequence;
026import org.jikesrvm.compilers.opt.ir.BasicBlock;
027import org.jikesrvm.compilers.opt.ir.Empty;
028import org.jikesrvm.compilers.opt.ir.IR;
029import org.jikesrvm.compilers.opt.ir.Instruction;
030import org.jikesrvm.compilers.opt.ir.Operator;
031
032/**
033 * This class inserts yield points in
034 * <ul>
035 *  <li>1) a method's prologue
036 *  <li>2) loop headers
037 *  <li>3) (optionally) method exits (epilogue, athrow)
038 * </ul>
039 */
040public class YieldPoints extends CompilerPhase {
041
042  /**
043   * Return the name of this phase
044   * @return "Yield Point Insertion"
045   */
046  @Override
047  public final String getName() {
048    return "Yield Point Insertion";
049  }
050
051  /**
052   * This phase contains no per-compilation instance fields.
053   */
054  @Override
055  public final CompilerPhase newExecution(IR ir) {
056    return this;
057  }
058
059  /**
060   * Insert yield points in method prologues, loop heads, and method exits
061   *
062   */
063  @Override
064  public final void perform(IR ir) {
065    if (!ir.method.isInterruptible()) {
066      return;   // don't insert yieldpoints in Uninterruptible code.
067    }
068
069    // (1) Insert prologue yieldpoint unconditionally.
070    //     As part of prologue/epilogue insertion we'll remove
071    //     the yieldpoints in trivial methods that otherwise wouldn't need
072    //     a stackframe.
073    prependYield(ir.cfg.entry(), YIELDPOINT_PROLOGUE, 0, ir.gc.getInlineSequence());
074
075    // (2) If using epilogue yieldpoints scan basic blocks, looking for returns or throws
076    if (VM.UseEpilogueYieldPoints) {
077      for (Enumeration<BasicBlock> e = ir.getBasicBlocks(); e.hasMoreElements();) {
078        BasicBlock block = e.nextElement();
079        if (block.hasReturn() || block.hasAthrowInst()) {
080          prependYield(block, YIELDPOINT_EPILOGUE, INSTRUMENTATION_BCI, ir.gc.getInlineSequence());
081        }
082      }
083    }
084
085    // (3) Insert yieldpoints in loop heads based on the LST.
086    LSTGraph lst = ir.HIRInfo.loopStructureTree;
087    if (lst != null) {
088      for (java.util.Enumeration<LSTNode> e = lst.getRoot().getChildren(); e.hasMoreElements();) {
089        processLoopNest(e.nextElement());
090      }
091    }
092  }
093
094  /**
095   * Process all loop heads in a loop nest by inserting a backedge yieldpoint in each of them.
096   *
097   * @param n a loop node
098   */
099  private void processLoopNest(LSTNode n) {
100    for (java.util.Enumeration<LSTNode> e = n.getChildren(); e.hasMoreElements();) {
101      processLoopNest(e.nextElement());
102    }
103    Instruction dest = n.header.firstInstruction();
104    if (dest.position.getMethod().isInterruptible()) {
105      prependYield(n.header, YIELDPOINT_BACKEDGE, dest.bcIndex, dest.position);
106    }
107  }
108
109  /**
110   * Add a YIELD instruction to the appropriate place for the basic
111   * block passed.
112   *
113   * @param bb the basic block
114   * @param yp the yieldpoint operator to insert
115   * @param bcIndex the bcIndex of the yieldpoint
116   * @param position the source position of the yieldpoint
117   */
118  private void prependYield(BasicBlock bb, Operator yp, int bcIndex, InlineSequence position) {
119    Instruction insertionPoint = null;
120
121    if (bb.isEmpty()) {
122      insertionPoint = bb.lastInstruction();
123    } else {
124      insertionPoint = bb.firstRealInstruction();
125    }
126
127    if (yp == YIELDPOINT_PROLOGUE) {
128      if (VM.VerifyAssertions) {
129        VM._assert((insertionPoint != null) && (insertionPoint.getOpcode() == IR_PROLOGUE_opcode));
130      }
131      // put it after the prologue
132      insertionPoint = insertionPoint.nextInstructionInCodeOrder();
133    } else if (VM.UseEpilogueYieldPoints && yp == YIELDPOINT_EPILOGUE) {
134      // epilogues go before the return or athrow (at end of block)
135      insertionPoint = bb.lastRealInstruction();
136    }
137
138    Instruction s = Empty.create(yp);
139    insertionPoint.insertBefore(s);
140    s.position = position;
141    s.bcIndex = bcIndex;
142  }
143}
144
145
146
147