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RemoveUnusedPrototypeProperties.java
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RemoveUnusedPrototypeProperties.java
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/*
* Copyright 2006 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 com.google.javascript.jscomp.AnalyzePrototypeProperties.NameInfo;
import com.google.javascript.jscomp.AnalyzePrototypeProperties.Symbol;
import com.google.javascript.rhino.Node;
import java.util.logging.Level;
import java.util.logging.Logger;
/**
* Removes unused properties from prototypes.
*
* NOTE: When canModifyExterns is true, this pass removes unused prototype properties
* in externs. This helped code size in the past, before type-based optimizations existed
* (and can help now for things that are not disambiguated), but is unsafe.
* For example, it can remove a polyfilled method that is not used in the source, but is
* used by the external code, so the call is not visible to the compiler.
* Therefore, the default for canModifyExterns is false, even though that increases code size
* for some projects.
*
* @author nicksantos@google.com (Nick Santos)
*/
class RemoveUnusedPrototypeProperties implements CompilerPass {
private static final Logger logger =
Logger.getLogger(RemoveUnusedPrototypeProperties.class.getName());
private final AbstractCompiler compiler;
private final boolean canModifyExterns;
private final boolean anchorUnusedVars;
/**
* Creates a new pass for removing unused prototype properties, based
* on the uniqueness of property names.
* @param compiler The compiler.
* @param canModifyExterns If true, then we can remove prototype
* properties that are declared in the externs file.
* @param anchorUnusedVars If true, then we must keep unused variables
* and the prototype properties they reference, even if they are
* never used.
*/
RemoveUnusedPrototypeProperties(AbstractCompiler compiler,
boolean canModifyExterns,
boolean anchorUnusedVars) {
this.compiler = compiler;
this.canModifyExterns = canModifyExterns;
this.anchorUnusedVars = anchorUnusedVars;
}
@Override
public void process(Node externRoot, Node root) {
AnalyzePrototypeProperties analyzer =
new AnalyzePrototypeProperties(
compiler,
null /* no module graph */,
canModifyExterns,
anchorUnusedVars,
false /* rootScopeUsesAreGlobal */);
analyzer.process(externRoot, root);
// Remove all properties under a given name if the property name is
// never referenced.
for (NameInfo nameInfo : analyzer.getAllNameInfo()) {
if (!nameInfo.isReferenced()) {
for (Symbol declaration : nameInfo.getDeclarations()) {
// Code-change reporting happens at the remove methods
declaration.remove(compiler);
}
if (logger.isLoggable(Level.FINE)) {
logger.fine("Removed unused prototype property: " + nameInfo.name);
}
}
}
}
}