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/*
 * Copyright 2008 Google Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not
 * use this file except in compliance with the License. You may obtain a copy of
 * the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 * License for the specific language governing permissions and limitations under
 * the License.
 */
package com.google.gwt.dev.jjs.impl;

import com.google.gwt.dev.jjs.SourceInfo;
import com.google.gwt.dev.jjs.ast.AccessModifier;
import com.google.gwt.dev.jjs.ast.Context;
import com.google.gwt.dev.jjs.ast.JClassType;
import com.google.gwt.dev.jjs.ast.JConditional;
import com.google.gwt.dev.jjs.ast.JDeclaredType;
import com.google.gwt.dev.jjs.ast.JExpression;
import com.google.gwt.dev.jjs.ast.JInterfaceType;
import com.google.gwt.dev.jjs.ast.JMethod;
import com.google.gwt.dev.jjs.ast.JMethodBody;
import com.google.gwt.dev.jjs.ast.JMethodCall;
import com.google.gwt.dev.jjs.ast.JModVisitor;
import com.google.gwt.dev.jjs.ast.JParameter;
import com.google.gwt.dev.jjs.ast.JParameterRef;
import com.google.gwt.dev.jjs.ast.JProgram;
import com.google.gwt.dev.jjs.ast.JProgram.DispatchType;
import com.google.gwt.dev.jjs.ast.JReferenceType;
import com.google.gwt.dev.jjs.ast.JReturnStatement;
import com.google.gwt.dev.jjs.ast.JTypeOracle;
import com.google.gwt.dev.jjs.ast.JVariableRef;
import com.google.gwt.dev.jjs.ast.RuntimeConstants;
import com.google.gwt.dev.jjs.ast.js.JsniMethodBody;
import com.google.gwt.dev.jjs.ast.js.JsniMethodRef;
import com.google.gwt.dev.jjs.impl.MakeCallsStatic.CreateStaticImplsVisitor;
import com.google.gwt.dev.jjs.impl.MakeCallsStatic.StaticCallConverter;
import com.google.gwt.dev.js.ast.JsContext;
import com.google.gwt.dev.js.ast.JsInvocation;
import com.google.gwt.dev.js.ast.JsModVisitor;
import com.google.gwt.dev.js.ast.JsNameRef;
import com.google.gwt.thirdparty.guava.common.collect.Iterables;
import com.google.gwt.thirdparty.guava.common.collect.Lists;
import com.google.gwt.thirdparty.guava.common.collect.Maps;
import com.google.gwt.thirdparty.guava.common.collect.Sets;

import java.util.Collections;
import java.util.EnumMap;
import java.util.EnumSet;
import java.util.List;
import java.util.Map;
import java.util.Set;

/**
 * Devirtualization is the process of converting virtual method calls on instances that might be
 * a JSO, a string or and array (like "obj.doFoo();") to static calls (like
 * "SomeClass.doFoo__devirtual$(obj)).
 *
 * This transformation is done on arrays, strings and JSOs virtual method calls; as this objects
 * do not have the virtual methods in their prototypes. The static version is a trampoline that
 * decides how to dispatch the method.
 *
 * See https://code.google.com/p/google-web-toolkit/wiki/OverlayTypes for why this is done for JSOs.
 * 
* * To complete the transformation: *
    *
  • * 1. methods that need to be devirtualized must be turned into static functions. *
  • *
  • * 2. all method calls to the original functions must be rerouted either to the new static * version or to a static dispatcher trampoline function that is created by this pass. *
  • *
* These trampolines are created whether a call to the function exists for separate compiled * modules to work. In a globally optimized build unused ones are pruned away.
* * This transform may NOT be run multiple times; it will create ever-expanding replacement * expressions. */ public class Devirtualizer { /** * Rewrite any virtual dispatches to Object, Strings or JavaScriptObject such that * dispatch occurs statically for JSOs, strings and arrays.
* * In the following cases JMethodCalls need to be rewritten: *
    *
  1. a dual dispatch interface
  2. *
  3. a single dispatch trough single-jso interface
  4. *
  5. a java.lang.Object override from JavaScriptObject
  6. *
  7. methods defined at String
  8. *
  9. in draftMode, a 'static' virtual JSO call that hasn't been made * static yet.
  10. *
* */ private class RewriteVirtualDispatches extends JModVisitor { @Override public void endVisit(JMethod x, Context ctx) { if (!mightNeedDevirtualization(x)) { return; } // The pruning pass will discard devirtualized methods that have not been called in // whole program optimizing mode. ensureDevirtualVersionExists(x); } @Override public void endVisit(JsniMethodRef x, Context ctx) { JMethod method = x.getTarget(); if (method == null || !mightNeedDevirtualization(method)) { return; } ensureDevirtualVersionExists(method); // Replace the JMethod in jsni reference to a reference to the devirtualized method. // Note that a JsniMethodRefs is a pair containing the Jsni reference as text (i.e. // "@java.lang.Boolean::booleanValue") and a reference to the actual JMethod in the AST; // in generation time the actual JMethod that is called is looked up from the reference text. // // Here we just replace the JMethod the reference is pointing to without updating the // reference text. // // Keeping the "key" unchanged avoid the necessity to sync up with the modifications in the // JS AST when the JsniMethodBody is processed. JMethod devirtualMethod = devirtualMethodByMethod.get(method); ctx.replaceMe(new JsniMethodRef( x.getSourceInfo(), x.getIdent(), devirtualMethod, program.getJavaScriptObject())); } @Override public void endVisit(JMethodCall x, Context ctx) { JMethod method = x.getTarget(); if (!method.needsDynamicDispatch()) { return; } JReferenceType instanceType = (JReferenceType) x.getInstance().getType().getUnderlyingType(); if (!mightNeedDevirtualization(method, instanceType)) { return; } // it is a super.m() call and the superclass is not a JSO. (this case is NOT reached if // MakeCallsStatic was called). if (x.isStaticDispatchOnly() && !method.isJsOverlay()) { return; } ensureDevirtualVersionExists(method); // Replaces this virtual method call with a static call to a devirtual version of the method. JMethod devirtualMethod = devirtualMethodByMethod.get(method); ctx.replaceMe(converter.convertCall(x, devirtualMethod)); } @Override public boolean visit(JMethod x, Context ctx) { // Don't rewrite the polymorphic call inside of the devirtualizing method! if (methodByDevirtualMethod.containsValue(x)) { return false; } return true; } @Override public boolean visit(JsniMethodBody x, Context ctx) { final Set devirtualMethodJsniIdentifiers = Sets.newHashSet(); for (JsniMethodRef jsniMethodRef : x.getJsniMethodRefs()) { JMethod target = jsniMethodRef.getTarget(); if (target != null && mightNeedDevirtualization(target)) { devirtualMethodJsniIdentifiers.add(jsniMethodRef.getIdent()); } } // Devirtualize jsni method calls. new JsModVisitor() { @Override public void endVisit(JsInvocation x, JsContext ctx) { if (!(x.getQualifier() instanceof JsNameRef)) { // If the invocation does not have a name as a qualifier then it is an expression and // cannot be a jsni method reference. return; } JsNameRef nameRef = (JsNameRef) x.getQualifier(); if (!nameRef.isJsniReference()) { // The invocation is not to a JSNI method. return; } // Retrieve the method referred by the JsniMethodRef and check whether it needs // devirtualization. if (!devirtualMethodJsniIdentifiers.contains(nameRef.getIdent())) { return; } // Devirtualize method by rewriting // [email protected]::booleanValue() ==> @java.lang.Boolean::booleanValue(a). // // Not the the reference identifier is *NOT* changed and will act a the key in the lookup // for the corresponding JMethod which is contained in the corresponding JsniMethodRef // node. ctx.replaceMe( new JsInvocation( x.getSourceInfo(), new JsNameRef( nameRef.getSourceInfo(), nameRef.getIdent()), Iterables.concat( Collections.singleton(nameRef.getQualifier()), x.getArguments()))); return; } }.accept(x.getFunc()); // Now go ahead and fix the corresponding JSNI references. return true; } /** * Constructs and caches a method that is a new static version of the given method or a * trampoline function that wraps a new static version of the given method. It chooses which to * construct based on how the given method's defining class relates to the JavascriptObject * class. */ private void ensureDevirtualVersionExists(JMethod method) { if (devirtualMethodByMethod.containsKey(method)) { // already did this one before return; } JDeclaredType targetType = method.getEnclosingType(); // Separate compilation treats all JSOs as if they are "dualImpl", as the interface might // be implemented by a regular Java object in a separate module. // TODO(rluble): (Separate compilation) Devirtualizer should be run before optimizations // and optimizations need to be strong enough to perform the same kind of size reductions // achieved by keeping track of singleImpls. if (method.getSignature().equals("toString()Ljava/lang/String;")) { // Object.toString is special because: 1) every JS object has it and 2) GWT creates // a bridge from toString to its implementation method. devirtualMethodByMethod.put( method, program.getIndexedMethod(RuntimeConstants.RUNTIME_TO_STRING)); } else if (!program.typeOracle.isDualJsoInterface(targetType) && program.typeOracle.isSingleJsoImpl(targetType)) { // Optimize the trampoline away when there is ONLY JSO dispatch. // TODO(rluble): verify that this case can not arise in optimized mode and if so // remove as is an unnecessary optimization. assert targetType instanceof JInterfaceType; assert !program.getTypeJavaLangString().getImplements().contains(targetType); JMethod overridingMethod = findOverridingMethod(method, program.typeOracle.getSingleJsoImpl(targetType)); assert overridingMethod != null; JMethod jsoStaticImpl = staticImplCreator.getOrCreateStaticImpl(program, overridingMethod); devirtualMethodByMethod.put(method, jsoStaticImpl); } else if (isOverlayMethod(method)) { // A virtual dispatch on a target that is already known to be an overlay method,. JMethod devirtualMethod = staticImplCreator.getOrCreateStaticImpl(program, method); devirtualMethodByMethod.put(method, devirtualMethod); } else { JMethod devirtualMethod = getOrCreateDevirtualMethod(method); devirtualMethodByMethod.put(method, devirtualMethod); } } private boolean mightNeedDevirtualization(JMethod method) { return mightNeedDevirtualization(method, method.getEnclosingType()); } private boolean mightNeedDevirtualization(JMethod method, JReferenceType instanceType) { if (instanceType == null || !method.needsDynamicDispatch()) { return false; } if (devirtualMethodByMethod.containsKey(method)) { return true; } if (isOverlayMethod(method)) { return true; } if (method.getEnclosingType().isJsNative()) { // Methods in a native JsType that are not JsOverlay should NOT be devirtualized. return false; } if (instanceType.isNullType()) { instanceType = method.getEnclosingType(); } EnumSet dispatchType = program.getDispatchType(instanceType); dispatchType.remove(DispatchType.HAS_JAVA_VIRTUAL_DISPATCH); return !dispatchType.isEmpty(); } } /** * Returns true if {@code method} is an overlay method. Overlay methods include the ones that * are marked as JsOverlay but also implicit overlays. */ private boolean isOverlayMethod(JMethod method) { return method.isJsOverlay() // Synthetic private methods on interfaces are the result of lambdas that capture the // enclosing instance and are defined on default methods; these can appear in native // interfaces and thus need to be treated as overlays. || (method.getEnclosingType() instanceof JInterfaceType && method.isPrivate()) // JsFunction implementation methods other than the other than the SAM implementation are // also considered overalys to allow for lighter weight JsFuncitons. // TODO(rluble): SAM implementation should also be devirtualized. || (method.getEnclosingType().isJsFunctionImplementation() && !method.isOrOverridesJsFunctionMethod()); } public static void exec(JProgram program) { new Devirtualizer(program).execImpl(); } /** * Maps each Object instance methods (ie, {@link Object#equals(Object)}) onto * its corresponding devirtualizing method. */ private Map devirtualMethodByMethod = Maps.newHashMap(); /** * Contains the Cast.hasJavaObjectVirtualDispatch method. */ private final JMethod hasJavaObjectVirtualDispatch; /** * Contains the Cast.isJavaArray method. */ private final JMethod isJavaArray; /** * Contains the set of devirtualizing methods that replace polymorphic calls * to Object methods. */ private final Map methodByDevirtualMethod = Maps.newHashMap(); private final JProgram program; private final CreateStaticImplsVisitor staticImplCreator; private final StaticCallConverter converter; /** * Creates and empty devirtualized method for devirtualizing {@code method} in class * {@code inclass}. */ private JMethod createDevirtualMethodFor(JMethod method, JDeclaredType inClass) { SourceInfo sourceInfo = method.getSourceInfo().makeChild(); String prefix = computeEscapedSignature(method.getSignature()); JMethod devirtualMethod = new JMethod(sourceInfo, prefix + "__devirtual$", inClass, method.getType(), false, true, true, AccessModifier.PUBLIC); // TODO(rluble): DoNotInline should be carried over if 'any' of the targets is marked so. devirtualMethod.setInliningMode(method.getInliningMode()); devirtualMethod.setBody(new JMethodBody(sourceInfo)); devirtualMethod.setSynthetic(); inClass.addMethod(devirtualMethod); // Setup parameters. devirtualMethod.createThisParameter(sourceInfo, method.getEnclosingType()); for (JParameter oldParam : method.getParams()) { devirtualMethod.createFinalParameter(sourceInfo, oldParam.getName(), oldParam.getType()); } devirtualMethod.freezeParamTypes(); devirtualMethod.addThrownExceptions(method.getThrownExceptions()); sourceInfo.addCorrelation(sourceInfo.getCorrelator().by(devirtualMethod)); return devirtualMethod; } /** * A normal method signature contains characters that are not valid in a method name. If you want * to construct a method name based on an existing method signature then those characters need to * be escaped. */ private static String computeEscapedSignature(String methodSignature) { return methodSignature.replaceAll("[\\<\\>\\(\\)\\;\\/\\[]", "_"); } private Devirtualizer(JProgram program) { this.program = program; this.hasJavaObjectVirtualDispatch = program.getIndexedMethod(RuntimeConstants.CAST_HAS_JAVA_OBJECT_VIRTUAL_DISPATCH); this.isJavaArray = program.getIndexedMethod(RuntimeConstants.ARRAY_IS_JAVA_ARRAY); // TODO: consider turning on null checks for "this"? // However, for JSO's there is existing code that relies on nulls being okay. this.converter = new StaticCallConverter(program, false); staticImplCreator = new CreateStaticImplsVisitor(program); } private void execImpl() { JClassType jsoType = program.getJavaScriptObject(); if (jsoType == null) { return; } new RewriteVirtualDispatches().accept(program); } /** * Finds the method that overrides this method, starting with the target * class. */ private JMethod findOverridingMethod(JMethod method, JClassType target) { if (target == null) { return null; } for (JMethod overridingMethod : target.getMethods()) { if (JTypeOracle.methodsDoMatch(method, overridingMethod)) { return overridingMethod; } } return findOverridingMethod(method, target.getSuperClass()); } /** * Construct conditional expression for dispatch. Handle the cases where a dispatch or check * is null indicating impossibility of such operation. */ private static JExpression constructMinimalCondition(JMethod checkMethod, JVariableRef target, JMethodCall trueDispatch, JExpression falseDispatch) { // TODO(rluble): Maybe we should emit slightly different code in checked mode, so that if // no condition is met an exception would be thrown rather than cascading. if (falseDispatch == null && trueDispatch == null) { return null; } if (falseDispatch == null) { // No need for condition to be evaluated. return trueDispatch; } if (trueDispatch == null || falseDispatch instanceof JMethodCall && ((JMethodCall) falseDispatch).getTarget() == trueDispatch.getTarget()) { // Both branches do the same dispatch (or no trueDispatch). return falseDispatch; } JMethodCall condition = new JMethodCall(trueDispatch.getSourceInfo(), null, checkMethod, target); return new JConditional(condition.getSourceInfo(), trueDispatch.getType(), condition, trueDispatch, falseDispatch); } /** * Create a dispatch call taking the arguments from the devirtual method. */ private static JMethodCall maybeCreateDispatch(JMethod dispatchTo, JMethod devirtualMethod) { if (dispatchTo == null) { return null; } List parameters = Lists.newArrayList(devirtualMethod.getParams()); SourceInfo sourceInfo = devirtualMethod.getSourceInfo(); JParameterRef thisParamRef = null; if (!dispatchTo.isStatic()) { // This is a virtual dispatch, take the first parameter as the receiver. thisParamRef = parameters.remove(0).makeRef(sourceInfo); } JMethodCall dispatchCall = new JMethodCall(sourceInfo, thisParamRef, dispatchTo); for (JParameter param : parameters) { dispatchCall.addArg(param.makeRef(sourceInfo)); } return dispatchCall; } /** * Create a conditional method to discriminate between static and virtual * dispatch. * *
   * static boolean equals__devirtual$(Object this, Object other) {
   *   return Cast.isJavaString() ? String.equals(other) :
   *       Cast.hasJavaObjectVirtualDispatch(this) ?
   *       this.equals(other) : JavaScriptObject.equals$(this, other);
   * }
   * 
*/ private JMethod getOrCreateDevirtualMethod(JMethod method) { if (methodByDevirtualMethod.containsKey(method)) { return methodByDevirtualMethod.get(method); } ///////////////////////////////////////////////////////////////// // 1. Determine which types of object are target of this dispatch ///////////////////////////////////////////////////////////////// JReferenceType enclosingType = method.getEnclosingType(); EnumSet possibleTargetTypes = program.getDispatchType( enclosingType.getUnderlyingType()); ///////////////////////////////////////////////////////////////// // 2. Compute the dispatch to method for each relevant case. ///////////////////////////////////////////////////////////////// EnumMap dispatchToMethodByTargetType = new EnumMap<>(DispatchType.class); for (Map.Entry nativeRepresentedType : program.getRepresentedAsNativeTypesDispatchMap().entrySet()) { // skip non-instantiated boxed types, which have been pruned from the AST. if (program.typeOracle.isInstantiatedType(nativeRepresentedType.getKey())) { maybeCreateDispatchFor(method, nativeRepresentedType.getValue(), possibleTargetTypes, dispatchToMethodByTargetType, nativeRepresentedType.getKey()); } } if (possibleTargetTypes.contains(DispatchType.JAVA_ARRAY)) { maybeCreateDispatchFor(method, DispatchType.JAVA_ARRAY, possibleTargetTypes, dispatchToMethodByTargetType, program.getTypeJavaLangObject()); } if (possibleTargetTypes.contains(DispatchType.JSO)) { JMethod overridingMethod = findOverridingMethod(method, program.typeOracle.getSingleJsoImpl(enclosingType)); if (overridingMethod == null && enclosingType == program.getTypeJavaLangObject()) { overridingMethod = findOverridingMethod(method, program.getJavaScriptObject()); } assert overridingMethod != null : method.getEnclosingType().getName() + "::" + method.getName() + " not overridden by JavaScriptObject"; dispatchToMethodByTargetType.put(DispatchType.JSO, staticImplCreator.getOrCreateStaticImpl(program, overridingMethod)); } if (possibleTargetTypes.contains(DispatchType.HAS_JAVA_VIRTUAL_DISPATCH)) { dispatchToMethodByTargetType.put(DispatchType.HAS_JAVA_VIRTUAL_DISPATCH, method); } ///////////////////////////////////////////////////////////////// // 3. Create a devirtualized method. ///////////////////////////////////////////////////////////////// // Decide where to place the devirtual method. Ideally these methods should reside in the // declaring type, but some of these will be interfaces and currently GWT does not emit // any code for them. // TODO(rluble): place interface methods in the corresponding interface once Java 8 defender // method support is implemented. JClassType devirtualMethodEnclosingClass = null; if (method.getEnclosingType() instanceof JClassType) { devirtualMethodEnclosingClass = (JClassType) method.getEnclosingType(); } else { for (Map.Entry nativeRepresentedType : program.getRepresentedAsNativeTypesDispatchMap().entrySet()) { if (dispatchToMethodByTargetType.containsKey(nativeRepresentedType.getValue())) { devirtualMethodEnclosingClass = nativeRepresentedType.getKey(); break; } } } if (devirtualMethodEnclosingClass == null) { if (dispatchToMethodByTargetType.get(DispatchType.JSO) != null) { // This is an interface method implemented by a JSO, place in the JSO class. devirtualMethodEnclosingClass = (JClassType) dispatchToMethodByTargetType.get(DispatchType.JSO).getEnclosingType(); } else { // It is an interface implemented by devirtualized types, place it in Object. devirtualMethodEnclosingClass = program.getTypeJavaLangObject(); } } // Devirtualization of external methods stays external and devirtualization of internal methods // stays internal. assert program.isReferenceOnly(devirtualMethodEnclosingClass) == program.isReferenceOnly(method.getEnclosingType()); // TODO(stalcup): devirtualization is modifying both internal and external types. Really // external types should never be modified. Change the point at which types are saved into // libraries to be after normalization has occurred, so that no further modification is // necessary when loading external types. JMethod devirtualMethod = createDevirtualMethodFor(method, devirtualMethodEnclosingClass); /** * Encoding */ SourceInfo sourceInfo = method.getSourceInfo().makeChild(); JParameter thisParam = devirtualMethod.getParams().get(0); // Synthesize the dispatch at a single conditional doing the checks in this order. // isString(obj) ? dispatchToString : ( // isRegularJavaObject(obj) ? obj.method : ( // isJavaArray(obj) ? // dispatchToArray : // dispatchToJSO // ) // ) // Construct back to fort. Last is JSO. JExpression dispatchExpression = maybeCreateDispatch(dispatchToMethodByTargetType.get(DispatchType.JSO), devirtualMethod); // Dispatch to array dispatchExpression = constructMinimalCondition( isJavaArray, thisParam.makeRef(thisParam.getSourceInfo()), maybeCreateDispatch(dispatchToMethodByTargetType.get(DispatchType.JAVA_ARRAY), devirtualMethod), dispatchExpression); // Dispatch to regular object dispatchExpression = constructMinimalCondition( hasJavaObjectVirtualDispatch, thisParam.makeRef(thisParam.getSourceInfo()), maybeCreateDispatch( dispatchToMethodByTargetType.get(DispatchType.HAS_JAVA_VIRTUAL_DISPATCH), devirtualMethod), dispatchExpression); // Dispatch to regular string, double, boolean for (Map.Entry nativeRepresentedType : program.getRepresentedAsNativeTypesDispatchMap().entrySet()) { DispatchType dispatchType = nativeRepresentedType.getValue(); String castInstanceOfQualifier = dispatchType.getTypeCategory().castInstanceOfQualifier(); dispatchExpression = constructMinimalCondition( program.getIndexedMethod("Cast.instanceOf" + castInstanceOfQualifier), thisParam.makeRef(thisParam.getSourceInfo()), maybeCreateDispatch(dispatchToMethodByTargetType.get(dispatchType), devirtualMethod), dispatchExpression); } // return dispatchConditional; JReturnStatement returnStatement = new JReturnStatement(sourceInfo, dispatchExpression); ((JMethodBody) devirtualMethod.getBody()).getBlock().addStmt(returnStatement); methodByDevirtualMethod.put(method, devirtualMethod); return devirtualMethod; } private void maybeCreateDispatchFor(JMethod method, DispatchType target, EnumSet possibleTargetTypes, EnumMap dispatchToMethodByTargetType, JClassType targetDevirtualType) { if (possibleTargetTypes.contains(target)) { JMethod overridingMethod = findOverridingMethod(method, targetDevirtualType); if (overridingMethod == null) { throw new AssertionError(method.getEnclosingType().getName() + "::" + method.getName() + " not overridden by " + targetDevirtualType.getSimpleName()); } dispatchToMethodByTargetType.put(target, staticImplCreator.getOrCreateStaticImpl(program, overridingMethod)); } } private static String getJsniReferenceIdentifier(JMethod method) { return "@" + method.getJsniSignature(true, false); } }




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