1 /*
   2  * Copyright (c) 2015, 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.  Oracle designates this
   8  * particular file as subject to the "Classpath" exception as provided
   9  * by Oracle in the LICENSE file that accompanied this code.
  10  *
  11  * This code is distributed in the hope that it will be useful, but WITHOUT
  12  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  13  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  14  * version 2 for more details (a copy is included in the LICENSE file that
  15  * accompanied this code).
  16  *
  17  * You should have received a copy of the GNU General Public License version
  18  * 2 along with this work; if not, write to the Free Software Foundation,
  19  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  20  *
  21  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  22  * or visit www.oracle.com if you need additional information or have any
  23  * questions.
  24  */
  25 
  26 package jdk.nashorn.internal.codegen;
  27 
  28 import java.util.ArrayDeque;
  29 import java.util.Collections;
  30 import java.util.Deque;
  31 import jdk.nashorn.internal.ir.FunctionNode;
  32 import jdk.nashorn.internal.ir.Node;
  33 import jdk.nashorn.internal.ir.Statement;
  34 import jdk.nashorn.internal.ir.visitor.SimpleNodeVisitor;
  35 import jdk.nashorn.internal.runtime.RecompilableScriptFunctionData;
  36 
  37 class CacheAst extends SimpleNodeVisitor {
  38     private final Deque<RecompilableScriptFunctionData> dataStack = new ArrayDeque<>();
  39 
  40     private final Compiler compiler;
  41 
  42     CacheAst(final Compiler compiler) {
  43         this.compiler = compiler;
  44         assert !compiler.isOnDemandCompilation();
  45     }
  46 
  47     @Override
  48     public boolean enterFunctionNode(final FunctionNode functionNode) {
  49         final int id = functionNode.getId();
  50         // It isn't necessary to keep a stack of RecompilableScriptFunctionData, but then we'd need to do a
  51         // potentially transitive lookup with compiler.getScriptFunctionData(id) for deeper functions; this way
  52         // we keep it constant time.
  53         dataStack.push(dataStack.isEmpty() ? compiler.getScriptFunctionData(id) : dataStack.peek().getScriptFunctionData(id));
  54         return true;
  55     }
  56 
  57     @Override
  58     public Node leaveFunctionNode(final FunctionNode functionNode) {
  59         final RecompilableScriptFunctionData data = dataStack.pop();
  60         if (functionNode.isSplit()) {
  61             // NOTE: cache only split function ASTs from eager pass. Caching non-split functions would require
  62             // some additional work, namely creating the concept of "uncacheable" function and reworking
  63             // ApplySpecialization to ensure that functions undergoing apply-to-call transformations are not
  64             // cacheable as well as recomputing Symbol.useCount when caching the eagerly parsed AST.
  65             // Recomputing Symbol.useCount would be needed so it will only reflect uses from within the
  66             // function being cached (and not reflect uses from its own nested functions or functions it is
  67             // nested in). This is consistent with the count an on-demand recompilation of the function would
  68             // produce. This is important as the decision to emit shared scope calls is based on this count,
  69             // and if it is not matched between a previous version of the code and its deoptimizing rest-of
  70             // compilation, it can result in rest-of not emitting a shared scope call where a previous version
  71             // of the code (compiled from a cached eager pre-pass seeing higher (global) useCount) would emit
  72             // it, causing a mismatch in stack shapes between previous code and its rest-of.
  73             data.setCachedAst(functionNode);
  74         }
  75 
  76         if (!dataStack.isEmpty() && ((dataStack.peek().getFunctionFlags() & FunctionNode.IS_SPLIT) != 0)) {
  77             // Return a function node with no body so that caching outer functions doesn't hold on to nested
  78             // functions' bodies. Note we're doing this only for functions directly nested inside split
  79             // functions, since we're only caching the split ones. It is not necessary to limit body removal
  80             // to just these functions, but it's a cheap way to prevent unnecessary AST mutations.
  81             return functionNode.setBody(lc, functionNode.getBody().setStatements(null, Collections.<Statement>emptyList()));
  82         }
  83         return functionNode;
  84     }
  85 }