sdk/lib/_internal/compiler/implementation/js_emitter/nsm_emitter.dart - sdk.git - Git at Google

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.

 part of dart2js.js_emitter;

 class NsmEmitter extends CodeEmitterHelper {
   final List<Selector> trivialNsmHandlers = <Selector>[];

   /// If this is true then we can generate the noSuchMethod handlers at startup
   /// time, instead of them being emitted as part of the Object class.
   bool get generateTrivialNsmHandlers => true;

   // If we need fewer than this many noSuchMethod handlers we can save space by
   // just emitting them in JS, rather than emitting the JS needed to generate
   // them at run time.
   static const VERY_FEW_NO_SUCH_METHOD_HANDLERS = 10;

   static const MAX_MINIFIED_LENGTH_FOR_DIFF_ENCODING = 4;

   void emitNoSuchMethodHandlers(AddPropertyFunction addProperty) {
     // Do not generate no such method handlers if there is no class.
     if (compiler.codegenWorld.instantiatedClasses.isEmpty) return;

     String noSuchMethodName = namer.publicInstanceMethodNameByArity(
         Compiler.NO_SUCH_METHOD, Compiler.NO_SUCH_METHOD_ARG_COUNT);

     // Keep track of the JavaScript names we've already added so we
     // do not introduce duplicates (bad for code size).
     Map<String, Selector> addedJsNames = new Map<String, Selector>();

     void addNoSuchMethodHandlers(String ignore, Set<Selector> selectors) {
       // Cache the object class and type.
       ClassElement objectClass = compiler.objectClass;
       DartType objectType = objectClass.rawType;

       for (Selector selector in selectors) {
         TypeMask mask = selector.mask;
         if (mask == null) {
           mask = new TypeMask.subclass(compiler.objectClass);
         }

         if (!mask.needsNoSuchMethodHandling(selector, compiler)) continue;
         String jsName = namer.invocationMirrorInternalName(selector);
         addedJsNames[jsName] = selector;
         String reflectionName = task.getReflectionName(selector, jsName);
         if (reflectionName != null) {
           task.mangledFieldNames[jsName] = reflectionName;
         }
       }
     }

     compiler.codegenWorld.invokedNames.forEach(addNoSuchMethodHandlers);
     compiler.codegenWorld.invokedGetters.forEach(addNoSuchMethodHandlers);
     compiler.codegenWorld.invokedSetters.forEach(addNoSuchMethodHandlers);

     // Set flag used by generateMethod helper below.  If we have very few
     // handlers we use addProperty for them all, rather than try to generate
     // them at runtime.
     bool haveVeryFewNoSuchMemberHandlers =
         (addedJsNames.length < VERY_FEW_NO_SUCH_METHOD_HANDLERS);

     jsAst.Expression generateMethod(String jsName, Selector selector) {
       // Values match JSInvocationMirror in js-helper library.
       int type = selector.invocationMirrorKind;
       List<String> parameterNames =
           new List.generate(selector.argumentCount, (i) => '\$$i');

       List<jsAst.Expression> argNames =
           selector.getOrderedNamedArguments().map((String name) =>
               js.string(name)).toList();

       String methodName = selector.invocationMirrorMemberName;
       String internalName = namer.invocationMirrorInternalName(selector);
       String reflectionName = task.getReflectionName(selector, internalName);
       if (!haveVeryFewNoSuchMemberHandlers &&
           isTrivialNsmHandler(type, argNames, selector, internalName) &&
           reflectionName == null) {
         trivialNsmHandlers.add(selector);
         return null;
       }

       assert(backend.isInterceptedName(Compiler.NO_SUCH_METHOD));
       jsAst.Expression expression = js('this.#(this, #(#, #, #, #, #))', [
           noSuchMethodName,
           namer.elementAccess(backend.getCreateInvocationMirror()),
           js.string(compiler.enableMinification ?
               internalName : methodName),
           js.string(internalName),
           js.number(type),
           new jsAst.ArrayInitializer.from(parameterNames.map(js)),
           new jsAst.ArrayInitializer.from(argNames)]);

       if (backend.isInterceptedName(selector.name)) {
         return js(r'function($receiver, #) { return # }',
                   [parameterNames, expression]);
       } else {
         return js(r'function(#) { return # }', [parameterNames, expression]);
       }
     }

     for (String jsName in addedJsNames.keys.toList()..sort()) {
       Selector selector = addedJsNames[jsName];
       jsAst.Expression method = generateMethod(jsName, selector);
       if (method != null) {
         addProperty(jsName, method);
         String reflectionName = task.getReflectionName(selector, jsName);
         if (reflectionName != null) {
           bool accessible = compiler.world.allFunctions.filter(selector).any(
               (Element e) => backend.isAccessibleByReflection(e));
           addProperty('+$reflectionName', js(accessible ? '2' : '0'));
         }
       }
     }
   }

   // Identify the noSuchMethod handlers that are so simple that we can
   // generate them programatically.
   bool isTrivialNsmHandler(
       int type, List argNames, Selector selector, String internalName) {
     if (!generateTrivialNsmHandlers) return false;
     // Check for interceptor calling convention.
     if (backend.isInterceptedName(selector.name)) {
       // We can handle the calling convention used by intercepted names in the
       // diff encoding, but we don't use that for non-minified code.
       if (!compiler.enableMinification) return false;
       String shortName = namer.invocationMirrorInternalName(selector);
       if (shortName.length > MAX_MINIFIED_LENGTH_FOR_DIFF_ENCODING) {
         return false;
       }
     }
     // Check for named arguments.
     if (argNames.length != 0) return false;
     // Check for unexpected name (this doesn't really happen).
     if (internalName.startsWith(namer.getterPrefix[0])) return type == 1;
     if (internalName.startsWith(namer.setterPrefix[0])) return type == 2;
     return type == 0;
   }

   /**
    * Adds (at runtime) the handlers to the Object class which catch calls to
    * methods that the object does not have.  The handlers create an invocation
    * mirror object.
    *
    * The current version only gives you the minified name when minifying (when
    * not minifying this method is not called).
    *
    * In order to generate the noSuchMethod handlers we only need the minified
    * name of the method.  We test the first character of the minified name to
    * determine if it is a getter or a setter, and we use the arguments array at
    * runtime to get the number of arguments and their values.  If the method
    * involves named arguments etc. then we don't handle it here, but emit the
    * handler method directly on the Object class.
    *
    * The minified names are mostly 1-4 character names, which we emit in sorted
    * order (primary key is length, secondary ordering is lexicographic).  This
    * gives an order like ... dD dI dX da ...
    *
    * Gzip is good with repeated text, but it can't diff-encode, so we do that
    * for it.  We encode the minified names in a comma-separated string, but all
    * the 1-4 character names are encoded before the first comma as a series of
    * base 26 numbers.  The last digit of each number is lower case, the others
    * are upper case, so 1 is "b" and 26 is "Ba".
    *
    * We think of the minified names as base 88 numbers using the ASCII
    * characters from # to z.  The base 26 numbers each encode the delta from
    * the previous minified name to the next.  So if there is a minified name
    * called Df and the next is Dh, then they are 2971 and 2973 when thought of
    * as base 88 numbers.  The difference is 2, which is "c" in lower-case-
    * terminated base 26.
    *
    * The reason we don't encode long minified names with this method is that
    * decoding the base 88 numbers would overflow JavaScript's puny integers.
    *
    * There are some selectors that have a special calling convention (because
    * they are called with the receiver as the first argument).  They need a
    * slightly different noSuchMethod handler, so we handle these first.
    */
   List<jsAst.Statement> buildTrivialNsmHandlers() {
     List<jsAst.Statement> statements = <jsAst.Statement>[];
     if (trivialNsmHandlers.length == 0) return statements;
     // Sort by calling convention, JS name length and by JS name.
     trivialNsmHandlers.sort((a, b) {
       bool aIsIntercepted = backend.isInterceptedName(a.name);
       bool bIsIntercepted = backend.isInterceptedName(b.name);
       if (aIsIntercepted != bIsIntercepted) return aIsIntercepted ? -1 : 1;
       String aName = namer.invocationMirrorInternalName(a);
       String bName = namer.invocationMirrorInternalName(b);
       if (aName.length != bName.length) return aName.length - bName.length;
       return aName.compareTo(bName);
     });

     // Find out how many selectors there are with the special calling
     // convention.
     int firstNormalSelector = trivialNsmHandlers.length;
     for (int i = 0; i < trivialNsmHandlers.length; i++) {
       if (!backend.isInterceptedName(trivialNsmHandlers[i].name)) {
         firstNormalSelector = i;
         break;
       }
     }

     // Get the short names (JS names, perhaps minified).
     Iterable<String> shorts = trivialNsmHandlers.map((selector) =>
          namer.invocationMirrorInternalName(selector));
     final diffShorts = <String>[];
     var diffEncoding = new StringBuffer();

     // Treat string as a number in base 88 with digits in ASCII order from # to
     // z.  The short name sorting is based on length, and uses ASCII order for
     // equal length strings so this means that names are ascending.  The hash
     // character, #, is never given as input, but we need it because it's the
     // implicit leading zero (otherwise we could not code names with leading
     // dollar signs).
     int fromBase88(String x) {
       int answer = 0;
       for (int i = 0; i < x.length; i++) {
         int c = x.codeUnitAt(i);
         // No support for Unicode minified identifiers in JS.
         assert(c >= $$ && c <= $z);
         answer *= 88;
         answer += c - $HASH;
       }
       return answer;
     }

     // Big endian encoding, A = 0, B = 1...
     // A lower case letter terminates the number.
     String toBase26(int x) {
       int c = x;
       var encodingChars = <int>[];
       encodingChars.add($a + (c % 26));
       while (true) {
         c ~/= 26;
         if (c == 0) break;
         encodingChars.add($A + (c % 26));
       }
       return new String.fromCharCodes(encodingChars.reversed.toList());
     }

     bool minify = compiler.enableMinification;
     bool useDiffEncoding = minify && shorts.length > 30;

     int previous = 0;
     int nameCounter = 0;
     for (String short in shorts) {
       // Emit period that resets the diff base to zero when we switch to normal
       // calling convention (this avoids the need to code negative diffs).
       if (useDiffEncoding && nameCounter == firstNormalSelector) {
         diffEncoding.write(".");
         previous = 0;
       }
       if (short.length <= MAX_MINIFIED_LENGTH_FOR_DIFF_ENCODING &&
           useDiffEncoding) {
         int base63 = fromBase88(short);
         int diff = base63 - previous;
         previous = base63;
         String base26Diff = toBase26(diff);
         diffEncoding.write(base26Diff);
       } else {
         if (useDiffEncoding || diffEncoding.length != 0) {
           diffEncoding.write(",");
         }
         diffEncoding.write(short);
       }
       nameCounter++;
     }

     // Startup code that loops over the method names and puts handlers on the
     // Object class to catch noSuchMethod invocations.
     ClassElement objectClass = compiler.objectClass;
     jsAst.Expression createInvocationMirror = namer.elementAccess(
         backend.getCreateInvocationMirror());
     String noSuchMethodName = namer.publicInstanceMethodNameByArity(
         Compiler.NO_SUCH_METHOD, Compiler.NO_SUCH_METHOD_ARG_COUNT);
     var type = 0;
     if (useDiffEncoding) {
       statements.add(js.statement('''{
           var objectClassObject =
                   collectedClasses[#],    // # is name of class Object.
               shortNames = #.split(","),  // # is diffEncoding.
               nameNumber = 0,
               diffEncodedString = shortNames[0],
               calculatedShortNames = [0, 1];    // 0, 1 are args for splice.
           // If we are loading a deferred library the object class will not be in
           // the collectedClasses so objectClassObject is undefined, and we skip
           // setting up the names.

           if (objectClassObject) {
             if (objectClassObject instanceof Array)
               objectClassObject = objectClassObject[1];
             for (var i = 0; i < diffEncodedString.length; i++) {
               var codes = [],
                   diff = 0,
                   digit = diffEncodedString.charCodeAt(i);
               if (digit == ${$PERIOD}) {
                 nameNumber = 0;
                 digit = diffEncodedString.charCodeAt(++i);
               }
               for (; digit <= ${$Z};) {
                 diff *= 26;
                 diff += (digit - ${$A});
                 digit = diffEncodedString.charCodeAt(++i);
               }
               diff *= 26;
               diff += (digit - ${$a});
               nameNumber += diff;
               for (var remaining = nameNumber;
                    remaining > 0;
                    remaining = (remaining / 88) | 0) {
                 codes.unshift(${$HASH} + remaining % 88);
               }
               calculatedShortNames.push(
                 String.fromCharCode.apply(String, codes));
             }
             shortNames.splice.apply(shortNames, calculatedShortNames);
           }
         }''', [
             js.string(namer.getNameOfClass(objectClass)),
             js.string('$diffEncoding')]));
     } else {
       // No useDiffEncoding version.
       Iterable<String> longs = trivialNsmHandlers.map((selector) =>
              selector.invocationMirrorMemberName);
       statements.add(js.statement(
           'var objectClassObject = collectedClasses[#],'
           '    shortNames = #.split(",")', [
               js.string(namer.getNameOfClass(objectClass)),
               js.string('$diffEncoding')]));
       if (!minify) {
         statements.add(js.statement('var longNames = #.split(",")',
                 js.string(longs.join(','))));
       }
       statements.add(js.statement(
           'if (objectClassObject instanceof Array)'
           '  objectClassObject = objectClassObject[1];'));
     }

     // TODO(9631): This is no longer valid for native methods.
     String whatToPatch = task.nativeEmitter.handleNoSuchMethod ?
                          "Object.prototype" :
                          "objectClassObject";

     List<jsAst.Expression> sliceOffsetArguments =
         firstNormalSelector == 0
         ? []
         : (firstNormalSelector == shorts.length
             ? [js.number(1)]
             : [js('(j < #) ? 1 : 0', js.number(firstNormalSelector))]);

     var sliceOffsetParams = sliceOffsetArguments.isEmpty ? [] : ['sliceOffset'];

     statements.add(js.statement('''
       // If we are loading a deferred library the object class will not be in
       // the collectedClasses so objectClassObject is undefined, and we skip
       // setting up the names.
       if (objectClassObject) {
         for (var j = 0; j < shortNames.length; j++) {
           var type = 0;
           var short = shortNames[j];
           if (short[0] == "${namer.getterPrefix[0]}") type = 1;
           if (short[0] == "${namer.setterPrefix[0]}") type = 2;
           // Generate call to:
           //
           //     createInvocationMirror(String name, internalName, type,
           //         arguments, argumentNames)
           //
           $whatToPatch[short] = (function(name, short, type, #) {
               return function() {
                 return this.#(this,
                     #(name, short, type,
                       Array.prototype.slice.call(arguments, #),
                       []));
               }
           })(#[j], short, type, #);
         }
       }''', [
           sliceOffsetParams,  // parameter
           noSuchMethodName,
           createInvocationMirror,
           sliceOffsetParams,  // argument to slice
           minify ? 'shortNames' : 'longNames',
           sliceOffsetArguments
       ]));

     return statements;
   }
 }
	// Copyright (c) 2013, the Dart project authors. Please see the AUTHORS file
	// for details. All rights reserved. Use of this source code is governed by a
	// BSD-style license that can be found in the LICENSE file.

	part of dart2js.js_emitter;

	class NsmEmitter extends CodeEmitterHelper {
	final List<Selector> trivialNsmHandlers = <Selector>[];

	/// If this is true then we can generate the noSuchMethod handlers at startup
	/// time, instead of them being emitted as part of the Object class.
	bool get generateTrivialNsmHandlers => true;

	// If we need fewer than this many noSuchMethod handlers we can save space by
	// just emitting them in JS, rather than emitting the JS needed to generate
	// them at run time.
	static const VERY_FEW_NO_SUCH_METHOD_HANDLERS = 10;

	static const MAX_MINIFIED_LENGTH_FOR_DIFF_ENCODING = 4;

	void emitNoSuchMethodHandlers(AddPropertyFunction addProperty) {
	// Do not generate no such method handlers if there is no class.
	if (compiler.codegenWorld.instantiatedClasses.isEmpty) return;

	String noSuchMethodName = namer.publicInstanceMethodNameByArity(
	Compiler.NO_SUCH_METHOD, Compiler.NO_SUCH_METHOD_ARG_COUNT);

	// Keep track of the JavaScript names we've already added so we
	// do not introduce duplicates (bad for code size).
	Map<String, Selector> addedJsNames = new Map<String, Selector>();

	void addNoSuchMethodHandlers(String ignore, Set<Selector> selectors) {
	// Cache the object class and type.
	ClassElement objectClass = compiler.objectClass;
	DartType objectType = objectClass.rawType;

	for (Selector selector in selectors) {
	TypeMask mask = selector.mask;
	if (mask == null) {
	mask = new TypeMask.subclass(compiler.objectClass);
	}

	if (!mask.needsNoSuchMethodHandling(selector, compiler)) continue;
	String jsName = namer.invocationMirrorInternalName(selector);
	addedJsNames[jsName] = selector;
	String reflectionName = task.getReflectionName(selector, jsName);
	if (reflectionName != null) {
	task.mangledFieldNames[jsName] = reflectionName;
	}
	}
	}

	compiler.codegenWorld.invokedNames.forEach(addNoSuchMethodHandlers);
	compiler.codegenWorld.invokedGetters.forEach(addNoSuchMethodHandlers);
	compiler.codegenWorld.invokedSetters.forEach(addNoSuchMethodHandlers);

	// Set flag used by generateMethod helper below. If we have very few
	// handlers we use addProperty for them all, rather than try to generate
	// them at runtime.
	bool haveVeryFewNoSuchMemberHandlers =
	(addedJsNames.length < VERY_FEW_NO_SUCH_METHOD_HANDLERS);

	jsAst.Expression generateMethod(String jsName, Selector selector) {
	// Values match JSInvocationMirror in js-helper library.
	int type = selector.invocationMirrorKind;
	List<String> parameterNames =
	new List.generate(selector.argumentCount, (i) => '\$$i');

	List<jsAst.Expression> argNames =
	selector.getOrderedNamedArguments().map((String name) =>
	js.string(name)).toList();

	String methodName = selector.invocationMirrorMemberName;
	String internalName = namer.invocationMirrorInternalName(selector);
	String reflectionName = task.getReflectionName(selector, internalName);
	if (!haveVeryFewNoSuchMemberHandlers &&
	isTrivialNsmHandler(type, argNames, selector, internalName) &&
	reflectionName == null) {
	trivialNsmHandlers.add(selector);
	return null;
	}

	assert(backend.isInterceptedName(Compiler.NO_SUCH_METHOD));
	jsAst.Expression expression = js('this.#(this, #(#, #, #, #, #))', [
	noSuchMethodName,
	namer.elementAccess(backend.getCreateInvocationMirror()),
	js.string(compiler.enableMinification ?
	internalName : methodName),
	js.string(internalName),
	js.number(type),
	new jsAst.ArrayInitializer.from(parameterNames.map(js)),
	new jsAst.ArrayInitializer.from(argNames)]);

	if (backend.isInterceptedName(selector.name)) {
	return js(r'function($receiver, #) { return # }',
	[parameterNames, expression]);
	} else {
	return js(r'function(#) { return # }', [parameterNames, expression]);
	}
	}

	for (String jsName in addedJsNames.keys.toList()..sort()) {
	Selector selector = addedJsNames[jsName];
	jsAst.Expression method = generateMethod(jsName, selector);
	if (method != null) {
	addProperty(jsName, method);
	String reflectionName = task.getReflectionName(selector, jsName);
	if (reflectionName != null) {
	bool accessible = compiler.world.allFunctions.filter(selector).any(
	(Element e) => backend.isAccessibleByReflection(e));
	addProperty('+$reflectionName', js(accessible ? '2' : '0'));
	}
	}
	}
	}

	// Identify the noSuchMethod handlers that are so simple that we can
	// generate them programatically.
	bool isTrivialNsmHandler(
	int type, List argNames, Selector selector, String internalName) {
	if (!generateTrivialNsmHandlers) return false;
	// Check for interceptor calling convention.
	if (backend.isInterceptedName(selector.name)) {
	// We can handle the calling convention used by intercepted names in the
	// diff encoding, but we don't use that for non-minified code.
	if (!compiler.enableMinification) return false;
	String shortName = namer.invocationMirrorInternalName(selector);
	if (shortName.length > MAX_MINIFIED_LENGTH_FOR_DIFF_ENCODING) {
	return false;
	}
	}
	// Check for named arguments.
	if (argNames.length != 0) return false;
	// Check for unexpected name (this doesn't really happen).
	if (internalName.startsWith(namer.getterPrefix[0])) return type == 1;
	if (internalName.startsWith(namer.setterPrefix[0])) return type == 2;
	return type == 0;
	}

	/**
	* Adds (at runtime) the handlers to the Object class which catch calls to
	* methods that the object does not have. The handlers create an invocation
	* mirror object.
	*
	* The current version only gives you the minified name when minifying (when
	* not minifying this method is not called).
	*
	* In order to generate the noSuchMethod handlers we only need the minified
	* name of the method. We test the first character of the minified name to
	* determine if it is a getter or a setter, and we use the arguments array at
	* runtime to get the number of arguments and their values. If the method
	* involves named arguments etc. then we don't handle it here, but emit the
	* handler method directly on the Object class.
	*
	* The minified names are mostly 1-4 character names, which we emit in sorted
	* order (primary key is length, secondary ordering is lexicographic). This
	* gives an order like ... dD dI dX da ...
	*
	* Gzip is good with repeated text, but it can't diff-encode, so we do that
	* for it. We encode the minified names in a comma-separated string, but all
	* the 1-4 character names are encoded before the first comma as a series of
	* base 26 numbers. The last digit of each number is lower case, the others
	* are upper case, so 1 is "b" and 26 is "Ba".
	*
	* We think of the minified names as base 88 numbers using the ASCII
	* characters from # to z. The base 26 numbers each encode the delta from
	* the previous minified name to the next. So if there is a minified name
	* called Df and the next is Dh, then they are 2971 and 2973 when thought of
	* as base 88 numbers. The difference is 2, which is "c" in lower-case-
	* terminated base 26.
	*
	* The reason we don't encode long minified names with this method is that
	* decoding the base 88 numbers would overflow JavaScript's puny integers.
	*
	* There are some selectors that have a special calling convention (because
	* they are called with the receiver as the first argument). They need a
	* slightly different noSuchMethod handler, so we handle these first.
	*/
	List<jsAst.Statement> buildTrivialNsmHandlers() {
	List<jsAst.Statement> statements = <jsAst.Statement>[];
	if (trivialNsmHandlers.length == 0) return statements;
	// Sort by calling convention, JS name length and by JS name.
	trivialNsmHandlers.sort((a, b) {
	bool aIsIntercepted = backend.isInterceptedName(a.name);
	bool bIsIntercepted = backend.isInterceptedName(b.name);
	if (aIsIntercepted != bIsIntercepted) return aIsIntercepted ? -1 : 1;
	String aName = namer.invocationMirrorInternalName(a);
	String bName = namer.invocationMirrorInternalName(b);
	if (aName.length != bName.length) return aName.length - bName.length;
	return aName.compareTo(bName);
	});

	// Find out how many selectors there are with the special calling
	// convention.
	int firstNormalSelector = trivialNsmHandlers.length;
	for (int i = 0; i < trivialNsmHandlers.length; i++) {
	if (!backend.isInterceptedName(trivialNsmHandlers[i].name)) {
	firstNormalSelector = i;
	break;
	}
	}

	// Get the short names (JS names, perhaps minified).
	Iterable<String> shorts = trivialNsmHandlers.map((selector) =>
	namer.invocationMirrorInternalName(selector));
	final diffShorts = <String>[];
	var diffEncoding = new StringBuffer();

	// Treat string as a number in base 88 with digits in ASCII order from # to
	// z. The short name sorting is based on length, and uses ASCII order for
	// equal length strings so this means that names are ascending. The hash
	// character, #, is never given as input, but we need it because it's the
	// implicit leading zero (otherwise we could not code names with leading
	// dollar signs).
	int fromBase88(String x) {
	int answer = 0;
	for (int i = 0; i < x.length; i++) {
	int c = x.codeUnitAt(i);
	// No support for Unicode minified identifiers in JS.
	assert(c >= $$ && c <= $z);
	answer *= 88;
	answer += c - $HASH;
	}
	return answer;
	}

	// Big endian encoding, A = 0, B = 1...
	// A lower case letter terminates the number.
	String toBase26(int x) {
	int c = x;
	var encodingChars = <int>[];
	encodingChars.add($a + (c % 26));
	while (true) {
	c ~/= 26;
	if (c == 0) break;
	encodingChars.add($A + (c % 26));
	}
	return new String.fromCharCodes(encodingChars.reversed.toList());
	}

	bool minify = compiler.enableMinification;
	bool useDiffEncoding = minify && shorts.length > 30;

	int previous = 0;
	int nameCounter = 0;
	for (String short in shorts) {
	// Emit period that resets the diff base to zero when we switch to normal
	// calling convention (this avoids the need to code negative diffs).
	if (useDiffEncoding && nameCounter == firstNormalSelector) {
	diffEncoding.write(".");
	previous = 0;
	}
	if (short.length <= MAX_MINIFIED_LENGTH_FOR_DIFF_ENCODING &&
	useDiffEncoding) {
	int base63 = fromBase88(short);
	int diff = base63 - previous;
	previous = base63;
	String base26Diff = toBase26(diff);
	diffEncoding.write(base26Diff);
	} else {
	if (useDiffEncoding \|\| diffEncoding.length != 0) {
	diffEncoding.write(",");
	}
	diffEncoding.write(short);
	}
	nameCounter++;
	}

	// Startup code that loops over the method names and puts handlers on the
	// Object class to catch noSuchMethod invocations.
	ClassElement objectClass = compiler.objectClass;
	jsAst.Expression createInvocationMirror = namer.elementAccess(
	backend.getCreateInvocationMirror());
	String noSuchMethodName = namer.publicInstanceMethodNameByArity(
	Compiler.NO_SUCH_METHOD, Compiler.NO_SUCH_METHOD_ARG_COUNT);
	var type = 0;
	if (useDiffEncoding) {
	statements.add(js.statement('''{
	var objectClassObject =
	collectedClasses[#], // # is name of class Object.
	shortNames = #.split(","), // # is diffEncoding.
	nameNumber = 0,
	diffEncodedString = shortNames[0],
	calculatedShortNames = [0, 1]; // 0, 1 are args for splice.
	// If we are loading a deferred library the object class will not be in
	// the collectedClasses so objectClassObject is undefined, and we skip
	// setting up the names.

	if (objectClassObject) {
	if (objectClassObject instanceof Array)
	objectClassObject = objectClassObject[1];
	for (var i = 0; i < diffEncodedString.length; i++) {
	var codes = [],
	diff = 0,
	digit = diffEncodedString.charCodeAt(i);
	if (digit == ${$PERIOD}) {
	nameNumber = 0;
	digit = diffEncodedString.charCodeAt(++i);
	}
	for (; digit <= ${$Z};) {
	diff *= 26;
	diff += (digit - ${$A});
	digit = diffEncodedString.charCodeAt(++i);
	}
	diff *= 26;
	diff += (digit - ${$a});
	nameNumber += diff;
	for (var remaining = nameNumber;
	remaining > 0;
	remaining = (remaining / 88) \| 0) {
	codes.unshift(${$HASH} + remaining % 88);
	}
	calculatedShortNames.push(
	String.fromCharCode.apply(String, codes));
	}
	shortNames.splice.apply(shortNames, calculatedShortNames);
	}
	}''', [
	js.string(namer.getNameOfClass(objectClass)),
	js.string('$diffEncoding')]));
	} else {
	// No useDiffEncoding version.
	Iterable<String> longs = trivialNsmHandlers.map((selector) =>
	selector.invocationMirrorMemberName);
	statements.add(js.statement(
	'var objectClassObject = collectedClasses[#],'
	' shortNames = #.split(",")', [
	js.string(namer.getNameOfClass(objectClass)),
	js.string('$diffEncoding')]));
	if (!minify) {
	statements.add(js.statement('var longNames = #.split(",")',
	js.string(longs.join(','))));
	}
	statements.add(js.statement(
	'if (objectClassObject instanceof Array)'
	' objectClassObject = objectClassObject[1];'));
	}

	// TODO(9631): This is no longer valid for native methods.
	String whatToPatch = task.nativeEmitter.handleNoSuchMethod ?
	"Object.prototype" :
	"objectClassObject";

	List<jsAst.Expression> sliceOffsetArguments =
	firstNormalSelector == 0
	? []
	: (firstNormalSelector == shorts.length
	? [js.number(1)]
	: [js('(j < #) ? 1 : 0', js.number(firstNormalSelector))]);

	var sliceOffsetParams = sliceOffsetArguments.isEmpty ? [] : ['sliceOffset'];

	statements.add(js.statement('''
	// If we are loading a deferred library the object class will not be in
	// the collectedClasses so objectClassObject is undefined, and we skip
	// setting up the names.
	if (objectClassObject) {
	for (var j = 0; j < shortNames.length; j++) {
	var type = 0;
	var short = shortNames[j];
	if (short[0] == "${namer.getterPrefix[0]}") type = 1;
	if (short[0] == "${namer.setterPrefix[0]}") type = 2;
	// Generate call to:
	//
	// createInvocationMirror(String name, internalName, type,
	// arguments, argumentNames)
	//
	$whatToPatch[short] = (function(name, short, type, #) {
	return function() {
	return this.#(this,
	#(name, short, type,
	Array.prototype.slice.call(arguments, #),
	[]));
	}
	})(#[j], short, type, #);
	}
	}''', [
	sliceOffsetParams, // parameter
	noSuchMethodName,
	createInvocationMirror,
	sliceOffsetParams, // argument to slice
	minify ? 'shortNames' : 'longNames',
	sliceOffsetArguments
	]));

	return statements;
	}
	}