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expand symbol space to improve compression (#2460)
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- give globally distinct names to distinct variables
- improve ability to compress cross-scoped
- introduce `options.rename` to `minify()`
- default `true` if both `compress` & `mangle`
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@alexlamsl
alexlamsl committed Nov 19, 2017
1 parent b80062c commit f4e2fb9
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Showing 4 changed files with 89 additions and 23 deletions.
2 changes: 2 additions & 0 deletions bin/uglifyjs
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Expand Up @@ -47,6 +47,7 @@ program.option("-d, --define <expr>[=value]", "Global definitions.", parse_js("d
program.option("--ie8", "Support non-standard Internet Explorer 8.");
program.option("--keep-fnames", "Do not mangle/drop function names. Useful for code relying on Function.prototype.name.");
program.option("--name-cache <file>", "File to hold mangled name mappings.");
program.option("--no-rename", "Disable symbol expansion.");
program.option("--self", "Build UglifyJS as a library (implies --wrap UglifyJS)");
program.option("--source-map [options]", "Enable source map/specify source map options.", parse_source_map());
program.option("--timings", "Display operations run time on STDERR.")
Expand All @@ -65,6 +66,7 @@ if (!program.output && program.sourceMap && program.sourceMap.url != "inline") {
"compress",
"ie8",
"mangle",
"rename",
"sourceMap",
"toplevel",
"wrap"
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12 changes: 11 additions & 1 deletion lib/minify.js
View file
Expand Up @@ -55,6 +55,7 @@ function minify(files, options) {
nameCache: null,
output: {},
parse: {},
rename: undefined,
sourceMap: false,
timings: false,
toplevel: false,
Expand All @@ -64,6 +65,9 @@ function minify(files, options) {
var timings = options.timings && {
start: Date.now()
};
if (options.rename === undefined) {
options.rename = options.compress && options.mangle;
}
set_shorthand("ie8", options, [ "compress", "mangle", "output" ]);
set_shorthand("keep_fnames", options, [ "compress", "mangle" ]);
set_shorthand("toplevel", options, [ "compress", "mangle" ]);
Expand Down Expand Up @@ -137,6 +141,11 @@ function minify(files, options) {
if (options.wrap) {
toplevel = toplevel.wrap_commonjs(options.wrap);
}
if (timings) timings.rename = Date.now();
if (options.rename) {
toplevel.figure_out_scope(options.mangle);
toplevel.expand_names(options.mangle);
}
if (timings) timings.compress = Date.now();
if (options.compress) toplevel = new Compressor(options.compress).compress(toplevel);
if (timings) timings.scope = Date.now();
Expand Down Expand Up @@ -197,7 +206,8 @@ function minify(files, options) {
if (timings) {
timings.end = Date.now();
result.timings = {
parse: 1e-3 * (timings.compress - timings.parse),
parse: 1e-3 * (timings.rename - timings.parse),
rename: 1e-3 * (timings.compress - timings.rename),
compress: 1e-3 * (timings.scope - timings.compress),
scope: 1e-3 * (timings.mangle - timings.scope),
mangle: 1e-3 * (timings.properties - timings.mangle),
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95 changes: 74 additions & 21 deletions lib/scope.js
View file
Expand Up @@ -43,7 +43,7 @@

"use strict";

function SymbolDef(scope, index, orig) {
function SymbolDef(scope, orig) {
this.name = orig.name;
this.orig = [ orig ];
this.eliminated = 0;
Expand All @@ -53,7 +53,6 @@ function SymbolDef(scope, index, orig) {
this.global = false;
this.mangled_name = null;
this.undeclared = false;
this.index = index;
this.id = SymbolDef.next_id++;
};

Expand Down Expand Up @@ -253,7 +252,7 @@ AST_Toplevel.DEFMETHOD("def_global", function(node){
if (globals.has(name)) {
return globals.get(name);
} else {
var g = new SymbolDef(this, globals.size(), node);
var g = new SymbolDef(this, node);
g.undeclared = true;
g.global = true;
globals.set(name, g);
Expand Down Expand Up @@ -314,7 +313,7 @@ AST_Scope.DEFMETHOD("def_function", function(symbol){
AST_Scope.DEFMETHOD("def_variable", function(symbol){
var def;
if (!this.variables.has(symbol.name)) {
def = new SymbolDef(this, this.variables.size(), symbol);
def = new SymbolDef(this, symbol);
this.variables.set(symbol.name, def);
def.global = !this.parent_scope;
} else {
Expand All @@ -332,7 +331,7 @@ AST_Scope.DEFMETHOD("next_mangled", function(options){

// https://github.com/mishoo/UglifyJS2/issues/242 -- do not
// shadow a name reserved from mangling.
if (options.reserved.indexOf(m) >= 0) continue;
if (member(m, options.reserved)) continue;

// we must ensure that the mangled name does not shadow a name
// from some parent scope that is referenced in this or in
Expand Down Expand Up @@ -384,7 +383,7 @@ AST_Symbol.DEFMETHOD("global", function(){
return this.definition().global;
});

AST_Toplevel.DEFMETHOD("_default_mangler_options", function(options){
AST_Toplevel.DEFMETHOD("_default_mangler_options", function(options) {
options = defaults(options, {
eval : false,
ie8 : false,
Expand All @@ -393,15 +392,14 @@ AST_Toplevel.DEFMETHOD("_default_mangler_options", function(options){
toplevel : false,
});
if (!Array.isArray(options.reserved)) options.reserved = [];
// Never mangle arguments
push_uniq(options.reserved, "arguments");
return options;
});

AST_Toplevel.DEFMETHOD("mangle_names", function(options){
options = this._default_mangler_options(options);

// Never mangle arguments
options.reserved.push('arguments');

// We only need to mangle declaration nodes. Special logic wired
// into the code generator will display the mangled name if it's
// present (and for AST_SymbolRef-s it'll use the mangled name of
Expand All @@ -410,11 +408,7 @@ AST_Toplevel.DEFMETHOD("mangle_names", function(options){
var to_mangle = [];

if (options.cache) {
this.globals.each(function(symbol){
if (options.reserved.indexOf(symbol.name) < 0) {
to_mangle.push(symbol);
}
});
this.globals.each(collect);
}

var tw = new TreeWalker(function(node, descend){
Expand All @@ -426,13 +420,7 @@ AST_Toplevel.DEFMETHOD("mangle_names", function(options){
return true; // don't descend again in TreeWalker
}
if (node instanceof AST_Scope) {
var p = tw.parent(), a = [];
node.variables.each(function(symbol){
if (options.reserved.indexOf(symbol.name) < 0) {
a.push(symbol);
}
});
to_mangle.push.apply(to_mangle, a);
node.variables.each(collect);
return;
}
if (node instanceof AST_Label) {
Expand All @@ -452,6 +440,71 @@ AST_Toplevel.DEFMETHOD("mangle_names", function(options){
if (options.cache) {
options.cache.cname = this.cname;
}

function collect(symbol) {
if (!member(symbol.name, options.reserved)) {
to_mangle.push(symbol);
}
}
});

AST_Toplevel.DEFMETHOD("find_unique_prefix", function(options) {
var letters = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ$_";
var cache = options.cache && options.cache.props;
var prefixes = Object.create(null);
options.reserved.forEach(add_prefix);
this.globals.each(add_def);
this.walk(new TreeWalker(function(node) {
if (node instanceof AST_Scope) node.variables.each(add_def);
}));
var prefix, i = 0;
do {
prefix = create_name(i++);
} while (prefixes[prefix]);
return prefix;

function add_prefix(name) {
if (/[0-9]$/.test(name)) {
prefixes[name.replace(/[0-9]+$/, "")] = true;
}
}

function add_def(def) {
var name = def.name;
if (def.global && cache && cache.has(name)) name = cache.get(name);
else if (!def.unmangleable(options)) return;
add_prefix(name);
}

function create_name(num) {
var name = "";
do {
name += letters[num % letters.length];
num = Math.floor(num / letters.length);
} while (num);
return name;
}
});

AST_Toplevel.DEFMETHOD("expand_names", function(options) {
options = this._default_mangler_options(options);
var prefix = this.find_unique_prefix(options);
this.globals.each(rename);
this.walk(new TreeWalker(function(node) {
if (node instanceof AST_Scope) node.variables.each(rename);
}));

function rename(def) {
if (def.global || def.unmangleable(options)) return;
if (member(def.name, options.reserved)) return;
var name = prefix + def.id;
def.orig.forEach(function(sym) {
sym.name = name;
});
def.references.forEach(function(sym) {
sym.name = name;
});
}
});

AST_Toplevel.DEFMETHOD("compute_char_frequency", function(options){
Expand Down
3 changes: 2 additions & 1 deletion test/mocha/minify.js
View file
Expand Up @@ -323,7 +323,8 @@ describe("minify", function() {
Uglify.minify(ast, {
compress: {
sequences: false
}
},
mangle: false
});
assert.ok(stat.body);
assert.strictEqual(stat.print_to_string(), "a=x()");
Expand Down

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