com.google.javascript.jscomp.DevirtualizeMethods Maven / Gradle / Ivy
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/*
* Copyright 2009 The Closure Compiler Authors.
*
* 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.javascript.jscomp;
import static com.google.common.base.Preconditions.checkArgument;
import static com.google.common.base.Preconditions.checkState;
import static com.google.common.base.Predicates.alwaysTrue;
import static com.google.common.collect.ImmutableList.toImmutableList;
import com.google.common.collect.ImmutableList;
import com.google.common.collect.ImmutableListMultimap;
import com.google.common.collect.Iterables;
import com.google.javascript.jscomp.OptimizeCalls.ReferenceMap;
import com.google.javascript.rhino.IR;
import com.google.javascript.rhino.JSDocInfo;
import com.google.javascript.rhino.Node;
import com.google.javascript.rhino.Token;
import java.util.ArrayList;
import java.util.Collection;
import java.util.List;
import java.util.Map;
import org.jspecify.nullness.Nullable;
/**
* Rewrites prototype and static methods as global, free functions that take the receiver as their
* first argument.
*
* This transformation simplifies the call graph so smart name removal, cross module code motion
* and other passes can do more.
*
*
To work effectively, this pass depends on {@link
* com.google.javascript.jscomp.disambiguate.DisambiguateProperties} running first to do a lot of
* heavy-lifting. It assumes that different methods will have unique names which in general isn't
* true for source JavaScript.
*
*
This pass should only be used in production code if property and variable renaming are turned
* on. Resulting code may also benefit from `--collapse_anonymous_functions` and
* `--collapse_variable_declarations`
*
*
This pass only rewrites functions that are part of a type's prototype or are statics on a
* ctor/interface function. A host of other preconditions must also be met. Functions that access
* the "arguments" variable arguments object are not eligible for this optimization, for example.
*
*
For example:
*
*
* A.prototype.accumulate = function(value) {
* this.total += value; return this.total
* }
* var total = a.accumulate(2)
*
*
* will be rewritten as:
*
*
* var accumulate = function(self, value) {
* self.total += value; return self.total
* }
* var total = accumulate(a, 2)
*
*
* A similar transformation occurs for:
*
*
* /** @constructor *\/
* function A() { }
*
* A.accumulate = function(value) {
* this.total += value; return this.total
* }
* var total = a.accumulate(2)
*
*/
class DevirtualizeMethods implements OptimizeCalls.CallGraphCompilerPass {
private final AbstractCompiler compiler;
private ReferenceMap refMap;
DevirtualizeMethods(AbstractCompiler compiler) {
this.compiler = compiler;
}
@Override
public void process(Node externs, Node root, ReferenceMap refMap) {
checkState(this.refMap == null, "`process` should only be called once.");
this.refMap = refMap;
for (Map.Entry> referenceGroup : refMap.getPropReferences()) {
processReferenceList(referenceGroup.getKey(), referenceGroup.getValue());
}
}
private void processReferenceList(String name, List sites) {
ImmutableListMultimap functionsBySite = ReferenceMap.getFunctionNodes(sites);
if (functionsBySite.isEmpty()) {
return; // We can't devirtualize without a definition.
}
// Use the first definition to ensure that all invocations are after the definition
// (temporally). It's possible that if class `A` is defined after class `B` there are calls to
// `A::foo` before `B::foo` is defined.
Node canonicalDefinitionSite = Iterables.get(functionsBySite.keySet(), 0);
ImmutableList callSites =
sites.stream()
// If a site has no associated functions, it must be a call site.
.filter((s) -> !functionsBySite.containsKey(s))
.collect(toImmutableList());
if (callSites.isEmpty()) {
return; // No need to devirtualize without calls.
}
// Check that this method is safe for devirtualization. These are in (estimated) increasing
// order of cost.
if (!functionsBySite.keySet().stream().allMatch((s) -> isEligibleDefinitionSite(name, s))) {
return;
} else if (!functionsBySite.values().stream().allMatch(this::isEligibleDefinitionFunction)) {
return;
} else if (!callSites.stream()
.allMatch((c) -> isEligibleCallSite(c, canonicalDefinitionSite))) {
return;
} else if (!allDefinitionsEquivalent(functionsBySite.values())) {
// Remember that this is only valid because we already checked the scoping of the definitions.
return;
}
String devirtualizedName = rewrittenMethodNameOf(name);
JSDocInfo bestJSDoc = NodeUtil.getBestJSDocInfo(canonicalDefinitionSite);
boolean isConstantName = bestJSDoc != null && bestJSDoc.isConstant();
for (Node callSite : callSites) {
rewriteCall(callSite, devirtualizedName, isConstantName);
}
// We only have to rewrite one definition. We've checked they're all identical so any of them
// can replace the others. The un-rewritten ones will be dead-code eliminated.
rewriteDefinition(canonicalDefinitionSite, devirtualizedName, isConstantName);
}
private boolean isPrototypeOrStaticMethodDefinition(Node node) {
Node parent = node.getParent();
Node grandparent = node.getGrandparent();
if (parent == null || grandparent == null) {
return false;
}
switch (node.getToken()) {
case MEMBER_FUNCTION_DEF:
if (NodeUtil.isEs6ConstructorMemberFunctionDef(node)) {
return false; // Constructors aren't methods.
}
return true;
case GETPROP:
{
// Case: `Foo.prototype.bar = function() { };
if (!node.isFirstChildOf(parent)
|| !NodeUtil.isExprAssign(grandparent)
|| !parent.getLastChild().isFunction()) {
return false;
}
if (NodeUtil.isPrototypeProperty(node)) {
return true;
}
if (isDefinitelyCtorOrInterface(node.getFirstChild())) {
return true;
}
return false;
}
case STRING_KEY:
{
// Case: `Foo.prototype = {
// bar: function() { },
// }`
checkArgument(parent.isObjectLit(), parent);
if (!parent.isSecondChildOf(grandparent)
|| !NodeUtil.isPrototypeAssignment(grandparent.getFirstChild())
|| !node.getFirstChild().isFunction()) {
return false;
}
return true;
}
default:
return false;
}
}
private boolean isDefinitelyCtorOrInterface(Node receiver) {
String qname = receiver.getQualifiedName();
if (qname == null) {
return false;
}
// It's safe to rely on the global scope because normalization has made all names unique. No
// local will shadow a global name, and we're ok with missing some statics.
Var var = refMap.getGlobalScope().getVar(qname);
if (var == null) {
return false;
}
if (var.isClass()) {
return true;
}
JSDocInfo jsdoc = var.getJSDocInfo();
if (jsdoc == null) {
return false;
} else if (jsdoc.isConstructorOrInterface()) {
return true; // Case: `@constructor`, `@interface`, `@record`.
}
return false;
}
/**
* Determines if a method definition site is eligible for rewrite as a global.
*
* In order to be eligible for rewrite, the definition site must:
*
*
* - Not be exported
*
- Be for a prototype method
*
*/
private boolean isEligibleDefinitionSite(String name, Node definitionSite) {
switch (definitionSite.getToken()) {
case GETPROP:
case MEMBER_FUNCTION_DEF:
case STRING_KEY:
case MEMBER_FIELD_DEF:
break;
default:
// No other node types are supported.
throw new IllegalArgumentException(definitionSite.toString());
}
// Exporting a method prevents rewrite.
CodingConvention codingConvention = compiler.getCodingConvention();
if (codingConvention.isExported(name, /* local= */ false)) {
return false;
}
if (!isPrototypeOrStaticMethodDefinition(definitionSite)) {
return false;
}
return true;
}
/**
* Determines if a method definition function is eligible for rewrite as a global function.
*
* In order to be eligible for rewrite, the definition function must:
*
*
* - Be instantiated exactly once
*
- Be the only possible implementation at a given site
*
- Not refer to its `arguments`; no implicit varags
*
- Not be an arrow function
*
*/
private boolean isEligibleDefinitionFunction(Node definitionFunction) {
checkArgument(definitionFunction.isFunction(), definitionFunction);
if (definitionFunction.isArrowFunction()) {
return false;
}
for (Node ancestor = definitionFunction.getParent();
ancestor != null;
ancestor = ancestor.getParent()) {
// The definition must be made exactly once. (i.e. not in a loop, conditional, or function)
if (isScopingOrBranchingConstruct(ancestor)) {
return false;
}
// TODO(nickreid): Support this so long as the definition doesn't reference the name.
// We can't allow this in general because references to the local name:
// - won't be rewritten correctly
// - won't be the same across multiple definitions, even if they are node-wise identical.
if (ancestor.isClass() && localNameIsDeclaredByClass(ancestor)) {
return false;
}
}
if (NodeUtil.has(definitionFunction, Node::isSuper, alwaysTrue())) {
// TODO(b/120452418): Remove this when we have a rewrite for `super`. We punted initially due
// to complexity.
return false;
}
if (NodeUtil.doesFunctionReferenceOwnArgumentsObject(definitionFunction)) {
// Functions that access "arguments" are not eligible since rewriting changes the structure of
// the function params.
return false;
}
return true;
}
/**
* Determines if a method call is eligible for rewrite as a global function.
*
* In order to be eligible for rewrite, the call must:
*
*
* - Property is never accessed outside a function call context.
*
*/
private boolean isEligibleCallSite(Node access, Node definitionSite) {
Node invocation = access.getParent();
if (!NodeUtil.isInvocationTarget(access) || !invocation.isCall()) {
// TODO(nickreid): Use the same definition of "a call" as
// `OptimizeCalls::ReferenceMap::isCallTarget`.
//
// Accessing the property in any way besides CALL has issues:
// - tear-off: invocations can't be tracked
// - as constructor: unsupported rewrite
// - as tagged template string: unsupported rewrite
// - as optional chaining call: original invocation target may be null/undefined and
// rewriting creates an unconditional call to a well-defined global function
return false;
}
// We can't rewrite functions called in modules that do not depend on the defining module.
// This is due to a subtle execution order change introduced by rewriting. Example:
//
// `x.foo().bar()` => `JSCompiler_StaticMethods_bar(x.foo())`
//
// Note how `JSCompiler_StaticMethods_bar` will be resolved before `x.foo()` is executed. In
// the case that `x.foo()` defines `JSCompiler_StaticMethods_bar` (e.g. by dynamically loading
// the defining module) this change in ordering will cause a `ReferenceError`. No error would
// be thrown by the original code because `bar` would be resolved later.
//
// We choose to use module ordering to avoid this issue because:
// - The other eligibility checks for devirtualization prevent any other dangerous cases
// that JSCompiler supports.
// - Rewriting all call-sites in a way that preserves exact ordering (e.g. using
// `ExpressionDecomposer`) has a significant code-size impact (circa 2018-11-19).
JSChunkGraph moduleGraph = compiler.getModuleGraph();
@Nullable JSChunk definitionModule = moduleForNode(definitionSite);
@Nullable JSChunk callModule = moduleForNode(access);
if (definitionModule == callModule) {
// Do nothing.
} else if (callModule == null) {
return false;
} else if (!moduleGraph.dependsOn(callModule, definitionModule)) {
return false;
}
return true;
}
/** Given a set of method definitions, verify they are the same. */
private boolean allDefinitionsEquivalent(Collection definitions) {
if (definitions.isEmpty()) {
return true;
}
Node definition = Iterables.get(definitions, 0);
checkArgument(definition.isFunction(), definition);
return definitions.stream().allMatch((d) -> compiler.areNodesEqualForInlining(d, definition));
}
/**
* Rewrites object method call sites as calls to global functions that take "this" as their first
* argument.
*
* Before: o.foo(a, b, c)
*
*
After: foo(o, a, b, c)
*/
private void rewriteCall(Node getprop, String newMethodName, boolean isConstantName) {
checkArgument(getprop.isGetProp(), getprop);
Node call = getprop.getParent();
checkArgument(call.isCall(), call);
Node receiver = getprop.getFirstChild();
// This rewriting does not exactly preserve order of operations; the newly inserted static
// method name will be resolved before `receiver` is evaluated. This is known to be safe due
// to the eligibility checks earlier in the pass.
//
// We choose not to do a full-fidelity rewriting (e.g. using `ExpressionDecomposer`) because
// doing so means extracting `receiver` into a new variable at each call-site. This has a
// significant code-size impact (circa 2018-11-19).
receiver.detach();
getprop.replaceWith(receiver);
Node newReceiver = IR.name(newMethodName).copyTypeFrom(getprop).srcref(getprop);
if (isConstantName) {
newReceiver.putBooleanProp(Node.IS_CONSTANT_NAME, true);
}
call.addChildToFront(newReceiver);
if (receiver.isSuper()) {
// Case: `super.foo(a, b)` => `foo(this, a, b)`
receiver.setToken(Token.THIS);
}
call.putBooleanProp(Node.FREE_CALL, true);
compiler.reportChangeToEnclosingScope(call);
}
/**
* Rewrites method definitions as global functions that take "this" as their first argument.
*
*
Before: a.prototype.b = function(a, b, c) {...}
*
*
After: var b = function(self, a, b, c) {...}
*/
private void rewriteDefinition(
Node definitionSite, String newMethodName, boolean isConstantName) {
final Node function;
final Node subtreeToRemove;
final Node nameSource;
switch (definitionSite.getToken()) {
case GETPROP:
function = definitionSite.getParent().getLastChild();
nameSource = definitionSite;
subtreeToRemove = NodeUtil.getEnclosingStatement(definitionSite);
break;
case STRING_KEY:
case MEMBER_FUNCTION_DEF:
function = definitionSite.getLastChild();
nameSource = definitionSite;
subtreeToRemove = definitionSite;
break;
default:
throw new IllegalArgumentException(definitionSite.toString());
}
// Define a new variable after the original declaration.
Node statement = NodeUtil.getEnclosingStatement(definitionSite);
Node newNameNode = IR.name(newMethodName).srcrefIfMissing(nameSource);
Node newVarNode = IR.var(newNameNode).srcrefIfMissing(nameSource);
newVarNode.insertBefore(statement);
if (isConstantName) {
newNameNode.putBooleanProp(Node.IS_CONSTANT_NAME, true);
}
// Copy the JSDocInfo, if any, from the original declaration
JSDocInfo originalJSDoc = NodeUtil.getBestJSDocInfo(definitionSite);
newVarNode.setJSDocInfo(originalJSDoc);
// Attach the function to the new variable.
function.detach();
newNameNode.addChildToFront(function);
// Create the `this` param.
String selfName = newMethodName + "$self";
Node paramList = function.getSecondChild();
paramList.addChildToFront(IR.name(selfName).srcrefIfMissing(function));
compiler.reportChangeToEnclosingScope(paramList);
// Eliminate `this`.
replaceReferencesToThis(function.getSecondChild(), selfName); // In default param values.
replaceReferencesToThis(function.getLastChild(), selfName); // In function body.
// Clean up dangling AST.
NodeUtil.deleteNode(subtreeToRemove, compiler);
compiler.reportChangeToEnclosingScope(newVarNode);
}
/** Replaces references to "this" with references to name. Do not traverse function boundaries. */
private void replaceReferencesToThis(Node node, String name) {
if (node.isFunction() && !node.isArrowFunction()) {
// Functions (besides arrows) create a new binding for `this`.
return;
}
for (Node child = node.getFirstChild(); child != null; ) {
final Node next = child.getNext();
if (child.isThis()) {
Node newName = IR.name(name).srcref(child).copyTypeFrom(child);
child.replaceWith(newName);
compiler.reportChangeToEnclosingScope(newName);
} else {
replaceReferencesToThis(child, name);
}
child = next;
}
}
private @Nullable JSChunk moduleForNode(Node node) {
Node script = NodeUtil.getEnclosingScript(node);
CompilerInput input = compiler.getInput(script.getInputId());
return input.getChunk();
}
private static String rewrittenMethodNameOf(String originalMethodName) {
return "JSCompiler_StaticMethods_" + originalMethodName;
}
/**
* Returns {@code true} iff a node may change the variable bindings of its subtree or cause that
* subtree to be executed not exactly once.
*
*
This method does not include CLASS because CLASS does not always create a new binding and it
* is important for the success of this optimization to consider class methods.
*
* @see {@link #localNameIsDeclaredByClass()}
*/
private static boolean isScopingOrBranchingConstruct(Node node) {
return NodeUtil.isControlStructure(node) // Branching.
|| node.isAnd() // Branching.
|| node.isOr() // Branching.
|| node.isFunction() // Branching & scoping.
|| node.isBlock(); // Scoping.
}
/**
* Returns {@code true} iff a CLASS subtree declares a name local to the class body.
*
*
Example:
*
*
{@code
* const Foo = class Bar {
* qux() { return Bar; }
* }
* }
*/
private static boolean localNameIsDeclaredByClass(Node clazz) {
checkArgument(clazz.isClass(), clazz);
if (clazz.getFirstChild().isEmpty()) {
return false; // There must be a name.
} else if (NodeUtil.isStatement(clazz)) {
return false; // The name must be local.
}
return true;
}
}