1 /*
   2  * Copyright (c) 2013, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.
   8  *
   9  * This code is distributed in the hope that it will be useful, but WITHOUT
  10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  12  * version 2 for more details (a copy is included in the LICENSE file that
  13  * accompanied this code).
  14  *
  15  * You should have received a copy of the GNU General Public License version
  16  * 2 along with this work; if not, write to the Free Software Foundation,
  17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  18  *
  19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  20  * or visit www.oracle.com if you need additional information or have any
  21  * questions.
  22  */
  23 package org.graalvm.compiler.lir;
  24 
  25 import java.util.ArrayList;
  26 
  27 import org.graalvm.compiler.core.common.cfg.AbstractBlockBase;
  28 import org.graalvm.compiler.lir.StandardOp.ImplicitNullCheck;
  29 import org.graalvm.compiler.lir.StandardOp.NullCheck;
  30 import org.graalvm.compiler.lir.gen.LIRGenerationResult;
  31 import org.graalvm.compiler.lir.phases.PostAllocationOptimizationPhase;
  32 
  33 import jdk.vm.ci.code.TargetDescription;
  34 
  35 public final class NullCheckOptimizer extends PostAllocationOptimizationPhase {
  36 
  37     @Override
  38     protected void run(TargetDescription target, LIRGenerationResult lirGenRes, PostAllocationOptimizationContext context) {
  39         LIR ir = lirGenRes.getLIR();
  40         AbstractBlockBase<?>[] blocks = ir.codeEmittingOrder();
  41         NullCheckOptimizer.foldNullChecks(ir, blocks, target.implicitNullCheckLimit);
  42     }
  43 
  44     private static void foldNullChecks(LIR ir, AbstractBlockBase<?>[] blocks, int implicitNullCheckLimit) {
  45         for (AbstractBlockBase<?> block : blocks) {
  46             if (block == null) {
  47                 continue;
  48             }
  49             ArrayList<LIRInstruction> list = ir.getLIRforBlock(block);
  50 
  51             if (!list.isEmpty()) {
  52 
  53                 LIRInstruction lastInstruction = list.get(0);
  54                 for (int i = 0; i < list.size(); i++) {
  55                     LIRInstruction instruction = list.get(i);
  56 
  57                     if (instruction instanceof ImplicitNullCheck && lastInstruction instanceof NullCheck) {
  58                         NullCheck nullCheck = (NullCheck) lastInstruction;
  59                         ImplicitNullCheck implicitNullCheck = (ImplicitNullCheck) instruction;
  60                         if (implicitNullCheck.makeNullCheckFor(nullCheck.getCheckedValue(), nullCheck.getState(), implicitNullCheckLimit)) {
  61                             list.remove(i - 1);
  62                             if (i < list.size()) {
  63                                 instruction = list.get(i);
  64                             }
  65                         }
  66                     }
  67                     lastInstruction = instruction;
  68                 }
  69             }
  70         }
  71     }
  72 
  73 }