JS: use native string to represent internals of java.lang.String

classlib/src/main/java/org/teavm/classlib/impl/JCLPlugin.java

@@ -29,6 +29,10 @@ import org.teavm.classlib.impl.currency.CurrencyHelper;
 import org.teavm.classlib.impl.lambda.LambdaMetafactorySubstitutor;
 import org.teavm.classlib.impl.record.ObjectMethodsSubstitutor;
 import org.teavm.classlib.impl.reflection.ReflectionTransformer;
+import org.teavm.classlib.impl.string.DefaultStringTransformer;
+import org.teavm.classlib.impl.string.JSStringConstructorGenerator;
+import org.teavm.classlib.impl.string.JSStringInjector;
+import org.teavm.classlib.impl.string.JSStringTransformer;
 import org.teavm.classlib.impl.tz.DateTimeZoneProvider;
 import org.teavm.classlib.impl.tz.DateTimeZoneProviderIntrinsic;
 import org.teavm.classlib.impl.tz.DateTimeZoneProviderPatch;
@@ -186,6 +190,16 @@ public class JCLPlugin implements TeaVMPlugin {
         installMetadata(host.getService(MetadataRegistration.class));
         host.add(new DeclaringClassDependencyListener());
         applyTimeZoneDetection(host);
+
+        var js = host.getExtension(TeaVMJavaScriptHost.class);
+        if (js != null) {
+            host.add(new JSStringTransformer());
+            js.addInjectorProvider(new JSStringInjector());
+            js.add(new MethodReference(String.class, "<init>", Object.class, void.class),
+                    new JSStringConstructorGenerator());
+        } else {
+            host.add(new DefaultStringTransformer());
+        }
     }
 
     private void applyTimeZoneDetection(TeaVMHost host) {

classlib/src/main/java/org/teavm/classlib/impl/string/DefaultStringTransformer.java

@@ -0,0 +1,280 @@
+/*
+ *  Copyright 2023 Alexey Andreev.
+ *
+ *  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 org.teavm.classlib.impl.string;
+
+import java.util.List;
+import org.teavm.model.AccessLevel;
+import org.teavm.model.ClassHolder;
+import org.teavm.model.ClassHolderTransformer;
+import org.teavm.model.ClassHolderTransformerContext;
+import org.teavm.model.FieldHolder;
+import org.teavm.model.FieldReference;
+import org.teavm.model.MethodReference;
+import org.teavm.model.Program;
+import org.teavm.model.ValueType;
+import org.teavm.model.instructions.ArrayElementType;
+import org.teavm.model.instructions.ArrayLengthInstruction;
+import org.teavm.model.instructions.ConstructArrayInstruction;
+import org.teavm.model.instructions.GetElementInstruction;
+import org.teavm.model.instructions.GetFieldInstruction;
+import org.teavm.model.instructions.IntegerConstantInstruction;
+import org.teavm.model.instructions.InvocationType;
+import org.teavm.model.instructions.InvokeInstruction;
+import org.teavm.model.instructions.PutFieldInstruction;
+import org.teavm.model.instructions.UnwrapArrayInstruction;
+
+public class DefaultStringTransformer implements ClassHolderTransformer {
+    @Override
+    public void transformClass(ClassHolder cls, ClassHolderTransformerContext context) {
+        if (cls.getName().equals("java.lang.String")) {
+            transformString(cls);
+        }
+    }
+
+    private void transformString(ClassHolder cls) {
+        var fields = List.copyOf(cls.getFields());
+        for (var field : fields) {
+            cls.removeField(field);
+        }
+
+        var charactersField = new FieldHolder("characters");
+        charactersField.setType(ValueType.arrayOf(ValueType.CHARACTER));
+        charactersField.setLevel(AccessLevel.PRIVATE);
+        cls.addField(charactersField);
+
+        for (var field : fields) {
+            cls.addField(field);
+        }
+
+        for (var method : cls.getMethods()) {
+            if (method.getProgram() != null) {
+                transformProgram(method.getProgram());
+            }
+        }
+    }
+
+    private void transformProgram(Program program) {
+        for (var block : program.getBasicBlocks()) {
+            for (var instruction : block) {
+                if (!(instruction instanceof InvokeInstruction)) {
+                    continue;
+                }
+                var invoke = (InvokeInstruction) instruction;
+                if (!invoke.getMethod().getClassName().equals("java.lang.String")) {
+                    continue;
+                }
+                switch (invoke.getMethod().getName()) {
+                    case "initWithEmptyChars":
+                        replaceInitWithEmptyChars(invoke);
+                        break;
+                    case "borrowChars":
+                        replaceBorrowChars(invoke);
+                        break;
+                    case "initWithCharArray":
+                        replaceInitWithCharArray(invoke);
+                        break;
+                    case "takeCharArray":
+                        replaceTakeCharArray(invoke);
+                        break;
+                    case "charactersLength":
+                        replaceCharactersLength(invoke);
+                        break;
+                    case "charactersGet":
+                        replaceCharactersGet(invoke);
+                        break;
+                    case "copyCharsToArray":
+                        replaceCopyCharsToArray(invoke);
+                        break;
+                    case "fastCharArray":
+                        replaceFastCharArray(invoke);
+                        break;
+                }
+            }
+        }
+    }
+
+    private void replaceInitWithEmptyChars(InvokeInstruction invoke) {
+        var program = invoke.getProgram();
+
+        var getField = new GetFieldInstruction();
+        getField.setField(new FieldReference("java.lang.String", "EMPTY_CHARS"));
+        getField.setFieldType(ValueType.arrayOf(ValueType.CHARACTER));
+        getField.setReceiver(program.createVariable());
+        getField.setLocation(invoke.getLocation());
+        invoke.insertNext(getField);
+
+        var putField = new PutFieldInstruction();
+        putField.setField(new FieldReference("java.lang.String", "characters"));
+        putField.setFieldType(ValueType.arrayOf(ValueType.CHARACTER));
+        putField.setInstance(invoke.getInstance());
+        putField.setValue(getField.getReceiver());
+        putField.setLocation(invoke.getLocation());
+        getField.insertNext(putField);
+
+        invoke.delete();
+    }
+
+    private void replaceBorrowChars(InvokeInstruction invoke) {
+        var program = invoke.getProgram();
+
+        var getField = new GetFieldInstruction();
+        getField.setField(new FieldReference("java.lang.String", "characters"));
+        getField.setFieldType(ValueType.arrayOf(ValueType.CHARACTER));
+        getField.setInstance(invoke.getArguments().get(0));
+        getField.setReceiver(program.createVariable());
+        getField.setLocation(invoke.getLocation());
+        invoke.insertNext(getField);
+
+        var putField = new PutFieldInstruction();
+        putField.setField(new FieldReference("java.lang.String", "characters"));
+        putField.setFieldType(ValueType.arrayOf(ValueType.CHARACTER));
+        putField.setInstance(invoke.getInstance());
+        putField.setValue(getField.getReceiver());
+        putField.setLocation(invoke.getLocation());
+        getField.insertNext(putField);
+
+        invoke.delete();
+    }
+
+    private void replaceInitWithCharArray(InvokeInstruction invoke) {
+        var program = invoke.getProgram();
+
+        var createArray = new ConstructArrayInstruction();
+        createArray.setItemType(ValueType.CHARACTER);
+        createArray.setSize(invoke.getArguments().get(2));
+        createArray.setReceiver(program.createVariable());
+        createArray.setLocation(invoke.getLocation());
+        invoke.insertNext(createArray);
+
+        var zero = new IntegerConstantInstruction();
+        zero.setReceiver(program.createVariable());
+        zero.setLocation(invoke.getLocation());
+        createArray.insertNext(zero);
+
+        var arrayCopy = new InvokeInstruction();
+        arrayCopy.setType(InvocationType.SPECIAL);
+        arrayCopy.setMethod(new MethodReference(System.class, "arraycopy", Object.class, int.class,
+                Object.class, int.class, int.class, void.class));
+        arrayCopy.setArguments(invoke.getArguments().get(0), invoke.getArguments().get(1),
+                createArray.getReceiver(), zero.getReceiver(), invoke.getArguments().get(2));
+        zero.insertNext(arrayCopy);
+
+        var putField = new PutFieldInstruction();
+        putField.setField(new FieldReference("java.lang.String", "characters"));
+        putField.setFieldType(ValueType.arrayOf(ValueType.CHARACTER));
+        putField.setInstance(program.variableAt(0));
+        putField.setValue(createArray.getReceiver());
+        putField.setLocation(invoke.getLocation());
+        arrayCopy.insertNext(putField);
+
+        invoke.delete();
+    }
+
+    private void replaceTakeCharArray(InvokeInstruction invoke) {
+        var putField = new PutFieldInstruction();
+        putField.setField(new FieldReference("java.lang.String", "characters"));
+        putField.setFieldType(ValueType.arrayOf(ValueType.CHARACTER));
+        putField.setInstance(invoke.getInstance());
+        putField.setValue(invoke.getArguments().get(0));
+        putField.setLocation(invoke.getLocation());
+        invoke.replace(putField);
+    }
+
+    private void replaceCharactersLength(InvokeInstruction invoke) {
+        var program = invoke.getProgram();
+
+        var getField = new GetFieldInstruction();
+        getField.setField(new FieldReference("java.lang.String", "characters"));
+        getField.setFieldType(ValueType.arrayOf(ValueType.CHARACTER));
+        getField.setInstance(invoke.getInstance());
+        getField.setReceiver(program.createVariable());
+        getField.setLocation(invoke.getLocation());
+        invoke.insertNext(getField);
+
+        var unwrapArray = new UnwrapArrayInstruction(ArrayElementType.CHAR);
+        unwrapArray.setArray(getField.getReceiver());
+        unwrapArray.setReceiver(program.createVariable());
+        unwrapArray.setLocation(invoke.getLocation());
+        getField.insertNext(unwrapArray);
+
+        var getLength = new ArrayLengthInstruction();
+        getLength.setArray(unwrapArray.getReceiver());
+        getLength.setReceiver(invoke.getReceiver());
+        getLength.setLocation(invoke.getLocation());
+        unwrapArray.insertNext(getLength);
+
+        invoke.delete();
+    }
+
+    private void replaceCharactersGet(InvokeInstruction invoke) {
+        var program = invoke.getProgram();
+
+        var getField = new GetFieldInstruction();
+        getField.setField(new FieldReference("java.lang.String", "characters"));
+        getField.setFieldType(ValueType.arrayOf(ValueType.CHARACTER));
+        getField.setInstance(invoke.getInstance());
+        getField.setReceiver(program.createVariable());
+        getField.setLocation(invoke.getLocation());
+        invoke.insertNext(getField);
+
+        var unwrapArray = new UnwrapArrayInstruction(ArrayElementType.CHAR);
+        unwrapArray.setArray(getField.getReceiver());
+        unwrapArray.setReceiver(program.createVariable());
+        unwrapArray.setLocation(invoke.getLocation());
+        getField.insertNext(unwrapArray);
+
+        var getFromArray = new GetElementInstruction(ArrayElementType.CHAR);
+        getFromArray.setArray(unwrapArray.getReceiver());
+        getFromArray.setReceiver(invoke.getReceiver());
+        getFromArray.setIndex(invoke.getArguments().get(0));
+        getFromArray.setLocation(invoke.getLocation());
+        unwrapArray.insertNext(getFromArray);
+
+        invoke.delete();
+    }
+
+    private void replaceCopyCharsToArray(InvokeInstruction invoke) {
+        var program = invoke.getProgram();
+
+        var getField = new GetFieldInstruction();
+        getField.setField(new FieldReference("java.lang.String", "characters"));
+        getField.setFieldType(ValueType.arrayOf(ValueType.CHARACTER));
+        getField.setInstance(invoke.getInstance());
+        getField.setReceiver(program.createVariable());
+        getField.setLocation(invoke.getLocation());
+        invoke.insertNext(getField);
+
+        var arrayCopy = new InvokeInstruction();
+        arrayCopy.setType(InvocationType.SPECIAL);
+        arrayCopy.setMethod(new MethodReference(System.class, "arraycopy", Object.class, int.class,
+                Object.class, int.class, int.class, void.class));
+        arrayCopy.setArguments(getField.getReceiver(), invoke.getArguments().get(0), invoke.getArguments().get(1),
+                invoke.getArguments().get(2), invoke.getArguments().get(3));
+        getField.insertNext(arrayCopy);
+
+        invoke.delete();
+    }
+
+    private void replaceFastCharArray(InvokeInstruction invoke) {
+        var getField = new GetFieldInstruction();
+        getField.setField(new FieldReference("java.lang.String", "characters"));
+        getField.setFieldType(ValueType.arrayOf(ValueType.CHARACTER));
+        getField.setInstance(invoke.getInstance());
+        getField.setReceiver(invoke.getReceiver());
+        getField.setLocation(invoke.getLocation());
+        invoke.replace(getField);
+    }
+}

classlib/src/main/java/org/teavm/classlib/impl/string/JSStringConstructorGenerator.java

@@ -0,0 +1,31 @@
+/*
+ *  Copyright 2023 Alexey Andreev.
+ *
+ *  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 org.teavm.classlib.impl.string;
+
+import java.io.IOException;
+import org.teavm.backend.javascript.codegen.SourceWriter;
+import org.teavm.backend.javascript.spi.Generator;
+import org.teavm.backend.javascript.spi.GeneratorContext;
+import org.teavm.model.MethodReference;
+
+public class JSStringConstructorGenerator implements Generator {
+    @Override
+    public void generate(GeneratorContext context, SourceWriter writer, MethodReference methodRef) throws IOException {
+        writer.append(context.getParameterName(0));
+        writer.append(".").appendField(JSStringInjector.NATIVE_FIELD).ws().append("=").ws();
+        writer.append(context.getParameterName(1)).append(";").softNewLine();
+    }
+}

classlib/src/main/java/org/teavm/classlib/impl/string/JSStringInjector.java

@@ -0,0 +1,234 @@
+/*
+ *  Copyright 2023 Alexey Andreev.
+ *
+ *  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 org.teavm.classlib.impl.string;
+
+import java.io.IOException;
+import java.util.function.Function;
+import org.teavm.backend.javascript.ProviderContext;
+import org.teavm.backend.javascript.spi.Injector;
+import org.teavm.backend.javascript.spi.InjectorContext;
+import org.teavm.model.FieldReference;
+import org.teavm.model.MethodReference;
+
+public class JSStringInjector implements Injector, Function<ProviderContext, Injector> {
+    static final FieldReference NATIVE_FIELD = new FieldReference("java.lang.String", "nativeString");
+
+    @Override
+    public Injector apply(ProviderContext providerContext) {
+        switch (providerContext.getMethod().getName()) {
+            case "initWithEmptyChars":
+            case "borrowChars":
+            case "initWithCharArray":
+            case "takeCharArray":
+            case "charactersLength":
+            case "charactersGet":
+            case "copyCharsToArray":
+            case "fastCharArray":
+            case "nativeString":
+            case "substringJS":
+            case "toLowerCaseJS":
+            case "toUpperCaseJS":
+            case "intern":
+            case "stripJS":
+            case "stripLeadingJS":
+            case "stripTrailingJS":
+                return this;
+        }
+        return null;
+    }
+
+    @Override
+    public void generate(InjectorContext context, MethodReference methodRef) throws IOException {
+        switch (methodRef.getName()) {
+            case "initWithEmptyChars":
+                initWithEmptyChars(context);
+                break;
+            case "borrowChars":
+                borrowChars(context);
+                break;
+            case "initWithCharArray":
+                initWithCharArray(context);
+                break;
+            case "takeCharArray":
+                takeCharArray(context);
+                break;
+            case "charactersLength":
+                charactersLength(context);
+                break;
+            case "charactersGet":
+                charactersGet(context);
+                break;
+            case "copyCharsToArray":
+                copyCharsToArray(context);
+                break;
+            case "fastCharArray":
+                fastCharArray(context);
+                break;
+            case "nativeString":
+                nativeString(context);
+                break;
+            case "substringJS":
+                substringJS(context);
+                break;
+            case "toLowerCaseJS":
+                toLowerCaseJS(context);
+                break;
+            case "toUpperCaseJS":
+                toUpperCaseJS(context);
+                break;
+            case "intern":
+                intern(context);
+                break;
+            case "stripJS":
+                stripJS(context);
+                break;
+            case "stripLeadingJS":
+                stripLeadingJS(context);
+                break;
+            case "stripTrailingJS":
+                stripTrailingJS(context);
+                break;
+        }
+    }
+
+    private void initWithEmptyChars(InjectorContext context) throws IOException {
+        var writer = context.getWriter();
+        context.writeExpr(context.getArgument(0));
+        writer.append(".").appendField(NATIVE_FIELD).ws().append("=").ws().append("\"\"");
+    }
+
+    private void borrowChars(InjectorContext context) throws IOException {
+        var writer = context.getWriter();
+        context.writeExpr(context.getArgument(0));
+        writer.append(".").appendField(NATIVE_FIELD).ws().append("=").ws();
+        context.writeExpr(context.getArgument(1));
+        writer.append(".").appendField(NATIVE_FIELD);
+    }
+
+    private void initWithCharArray(InjectorContext context) throws IOException {
+        var writer = context.getWriter();
+        context.writeExpr(context.getArgument(0));
+        writer.append(".").appendField(NATIVE_FIELD).ws().append("=").ws();
+        writer.append("$rt_charArrayToString").append("(");
+        context.writeExpr(context.getArgument(1));
+        writer.append(".data,").ws();
+        context.writeExpr(context.getArgument(2));
+        writer.append(",").ws();
+        context.writeExpr(context.getArgument(3));
+        writer.append(")");
+    }
+
+    private void takeCharArray(InjectorContext context) throws IOException {
+        var writer = context.getWriter();
+        context.writeExpr(context.getArgument(0));
+        writer.append(".").appendField(NATIVE_FIELD).ws().append("=").ws();
+        writer.append("$rt_fullArrayToString").append("(");
+        context.writeExpr(context.getArgument(1));
+        writer.append(".data)");
+    }
+
+    private void charactersLength(InjectorContext context) throws IOException {
+        var writer = context.getWriter();
+        context.writeExpr(context.getArgument(0));
+        writer.append(".").appendField(NATIVE_FIELD).append(".length");
+    }
+
+    private void charactersGet(InjectorContext context) throws IOException {
+        var writer = context.getWriter();
+        context.writeExpr(context.getArgument(0));
+        writer.append(".").appendField(NATIVE_FIELD).append(".charCodeAt(");
+        context.writeExpr(context.getArgument(1));
+        writer.append(")");
+    }
+
+    private void copyCharsToArray(InjectorContext context) throws IOException {
+        var writer = context.getWriter();
+        writer.append("$rt_stringToCharArray").append("(");
+        context.writeExpr(context.getArgument(0));
+        writer.append(".").appendField(NATIVE_FIELD);
+        writer.append(",").ws();
+        context.writeExpr(context.getArgument(1));
+        writer.append(",").ws();
+        context.writeExpr(context.getArgument(2));
+        writer.append(".data");
+        writer.append(",").ws();
+        context.writeExpr(context.getArgument(3));
+        writer.append(",").ws();
+        context.writeExpr(context.getArgument(4));
+        writer.append(")");
+    }
+
+    private void substringJS(InjectorContext context) throws IOException {
+        var writer = context.getWriter();
+        context.writeExpr(context.getArgument(0));
+        writer.append(".substring(");
+        context.writeExpr(context.getArgument(1));
+        writer.append(",").ws();
+        context.writeExpr(context.getArgument(2));
+        writer.append(")");
+    }
+
+    private void fastCharArray(InjectorContext context) throws IOException {
+        var writer = context.getWriter();
+        writer.append("$rt_fastStringToCharArray").append("(");
+        context.writeExpr(context.getArgument(0));
+        writer.append(".").appendField(NATIVE_FIELD);
+        writer.append(")");
+    }
+
+    private void nativeString(InjectorContext context) throws IOException {
+        var writer = context.getWriter();
+        context.writeExpr(context.getArgument(0));
+        writer.append(".").appendField(NATIVE_FIELD);
+    }
+
+    private void toLowerCaseJS(InjectorContext context) throws IOException {
+        var writer = context.getWriter();
+        context.writeExpr(context.getArgument(0));
+        writer.append(".toLowerCase()");
+    }
+
+    private void toUpperCaseJS(InjectorContext context) throws IOException {
+        var writer = context.getWriter();
+        context.writeExpr(context.getArgument(0));
+        writer.append(".toUpperCase()");
+    }
+
+    private void intern(InjectorContext context) throws IOException {
+        var writer = context.getWriter();
+        writer.appendFunction("$rt_intern").append("(");
+        context.writeExpr(context.getArgument(0));
+        writer.append(")");
+    }
+
+    private void stripJS(InjectorContext context) throws IOException {
+        var writer = context.getWriter();
+        context.writeExpr(context.getArgument(0));
+        writer.append(".trim()");
+    }
+
+    private void stripLeadingJS(InjectorContext context) throws IOException {
+        var writer = context.getWriter();
+        context.writeExpr(context.getArgument(0));
+        writer.append(".trimStart()");
+    }
+
+    private void stripTrailingJS(InjectorContext context) throws IOException {
+        var writer = context.getWriter();
+        context.writeExpr(context.getArgument(0));
+        writer.append(".trimEnd()");
+    }
+}

classlib/src/main/java/org/teavm/classlib/impl/string/JSStringTransformer.java

@@ -0,0 +1,44 @@
+/*
+ *  Copyright 2023 Alexey Andreev.
+ *
+ *  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 org.teavm.classlib.impl.string;
+
+import org.teavm.interop.NoSideEffects;
+import org.teavm.model.AccessLevel;
+import org.teavm.model.AnnotationHolder;
+import org.teavm.model.ClassHolder;
+import org.teavm.model.ClassHolderTransformer;
+import org.teavm.model.ClassHolderTransformerContext;
+import org.teavm.model.ElementModifier;
+import org.teavm.model.FieldHolder;
+import org.teavm.model.MethodDescriptor;
+import org.teavm.model.ValueType;
+
+public class JSStringTransformer implements ClassHolderTransformer {
+    @Override
+    public void transformClass(ClassHolder cls, ClassHolderTransformerContext context) {
+        if (cls.getName().equals("java.lang.String")) {
+            var charactersField = new FieldHolder("nativeString");
+            charactersField.setType(ValueType.object("java.lang.Object"));
+            charactersField.setLevel(AccessLevel.PRIVATE);
+            cls.addField(charactersField);
+
+            var method = cls.getMethod(new MethodDescriptor("<init>", Object.class, void.class));
+            method.setProgram(null);
+            method.getModifiers().add(ElementModifier.NATIVE);
+            method.getAnnotations().add(new AnnotationHolder(NoSideEffects.class.getName()));
+        }
+    }
+}

classlib/src/main/java/org/teavm/classlib/java/lang/StringNativeDependency.java

@@ -15,23 +15,12 @@
  */
 package org.teavm.classlib.java.lang;
 
-import java.io.IOException;
-import org.teavm.backend.javascript.codegen.SourceWriter;
-import org.teavm.backend.javascript.spi.Generator;
-import org.teavm.backend.javascript.spi.GeneratorContext;
 import org.teavm.dependency.DependencyAgent;
 import org.teavm.dependency.DependencyPlugin;
 import org.teavm.dependency.MethodDependency;
 import org.teavm.model.MethodReference;
 
-public class StringNativeGenerator implements Generator, DependencyPlugin {
+public class StringNativeDependency implements DependencyPlugin {
-    @Override
-    public void generate(GeneratorContext context, SourceWriter writer, MethodReference methodRef) throws IOException {
-        if (methodRef.getName().equals("intern")) {
-            writer.append("return $rt_intern(").append(context.getParameterName(0)).append(");").softNewLine();
-        }
-    }
-
     @Override
     public void methodReached(DependencyAgent agent, MethodDependency method) {
         if (method.getReference().getName().equals("intern")) {

classlib/src/main/java/org/teavm/classlib/java/lang/TString.java

@@ -16,7 +16,7 @@
 package org.teavm.classlib.java.lang;
 
 import java.util.Locale;
-import org.teavm.backend.javascript.spi.GeneratedBy;
+import org.teavm.classlib.PlatformDetector;
 import org.teavm.classlib.java.io.TSerializable;
 import org.teavm.classlib.java.io.TUnsupportedEncodingException;
 import org.teavm.classlib.java.nio.TByteBuffer;
@@ -35,32 +35,50 @@ public class TString extends TObject implements TSerializable, TComparable<TStri
     private static final char[] EMPTY_CHARS = new char[0];
     private static final TString EMPTY = new TString();
     public static final TComparator<TString> CASE_INSENSITIVE_ORDER = (o1, o2) -> o1.compareToIgnoreCase(o2);
-    private char[] characters;
     private transient int hashCode;
 
     public TString() {
-        this.characters = EMPTY_CHARS;
+        initWithEmptyChars();
     }
 
+    @NoSideEffects
+    private native void initWithEmptyChars();
+
     public TString(TString other) {
-        characters = other.characters;
+        borrowChars(other);
     }
 
+    @NoSideEffects
+    private native void borrowChars(TString other);
+
     public TString(char[] characters) {
         this(characters, 0, characters.length);
     }
 
-    public TString(char[] value, int offset, int count) {
+    public TString(Object nativeString) {
-        this.characters = new char[count];
-        System.arraycopy(value, offset, this.characters, 0, count);
     }
 
+    private native Object nativeString();
+
+    public TString(char[] value, int offset, int count) {
+        if (offset < 0 || count < 0 || offset + count > value.length) {
+            throw new IndexOutOfBoundsException();
+        }
+        initWithCharArray(value, offset, count);
+    }
+
+    @NoSideEffects
+    private native void initWithCharArray(char[] value, int offset, int count);
+
     static TString fromArray(char[] characters) {
         var s = new TString();
-        s.characters = characters;
+        s.takeCharArray(characters);
         return s;
     }
 
+    @NoSideEffects
+    private native void takeCharArray(char[] characters);
+
     public TString(byte[] bytes, int offset, int length, TString charsetName) throws TUnsupportedEncodingException {
         this(bytes, offset, length, TCharset.forName(charsetName.toString()));
     }
@@ -86,7 +104,7 @@ public class TString extends TObject implements TSerializable, TComparable<TStri
     }
 
     public TString(int[] codePoints, int offset, int count) {
-        characters = new char[count * 2];
+        var characters = new char[count * 2];
         int charCount = 0;
         for (int i = 0; i < count; ++i) {
             int codePoint = codePoints[offset++];
@@ -100,16 +118,19 @@ public class TString extends TObject implements TSerializable, TComparable<TStri
         if (charCount < characters.length) {
             characters = TArrays.copyOf(characters, charCount);
         }
+        takeCharArray(characters);
     }
 
     private void initWithBytes(byte[] bytes, int offset, int length, TCharset charset) {
         TCharBuffer buffer = charset.decode(TByteBuffer.wrap(bytes, offset, length));
+        char[] characters;
         if (buffer.hasArray() && buffer.position() == 0 && buffer.limit() == buffer.capacity()) {
             characters = buffer.array();
         } else {
             characters = new char[buffer.remaining()];
             buffer.get(characters);
         }
+        takeCharArray(characters);
     }
 
     public TString(TStringBuilder sb) {
@@ -117,7 +138,7 @@ public class TString extends TObject implements TSerializable, TComparable<TStri
     }
 
     private TString(int length) {
-        this.characters = new char[length];
+        takeCharArray(new char[length]);
     }
 
     private static TString allocate(int size) {
@@ -126,10 +147,10 @@ public class TString extends TObject implements TSerializable, TComparable<TStri
 
     @Override
     public char charAt(int index) {
-        if (index < 0 || index >= characters.length) {
+        if (index < 0 || index >= charactersLength()) {
             throw new TStringIndexOutOfBoundsException();
         }
-        return characters[index];
+        return charactersGet(index);
     }
 
     public int codePointAt(int index) {
@@ -150,17 +171,23 @@ public class TString extends TObject implements TSerializable, TComparable<TStri
 
     @Override
     public int length() {
-        return characters.length;
+        return charactersLength();
     }
 
+    @NoSideEffects
+    private native int charactersLength();
+
+    @NoSideEffects
+    private native char charactersGet(int index);
+
     @Override
     public boolean isEmpty() {
-        return characters.length == 0;
+        return charactersLength() == 0;
     }
     
     public boolean isBlank() {
-        for (int i = 0; i < characters.length; i++) {
+        for (int i = 0; i < charactersLength(); i++) {
-            if (characters[i] != ' ') {
+            if (charactersGet(i) != ' ') {
                 return false;
             }
         }
@@ -172,15 +199,18 @@ public class TString extends TObject implements TSerializable, TComparable<TStri
                 || dstBegin + (srcEnd - srcBegin) > dst.length) {
             throw new TIndexOutOfBoundsException();
         }
-        System.arraycopy(characters, srcBegin, dst, dstBegin, srcEnd - srcBegin);
+        copyCharsToArray(srcBegin, dst, dstBegin, srcEnd - srcBegin);
     }
 
+    @NoSideEffects
+    private native void copyCharsToArray(int begin, char[] dst, int dstBegin, int length);
+
     public boolean contentEquals(TStringBuffer buffer) {
-        if (characters.length != buffer.length()) {
+        if (charactersLength() != buffer.length()) {
             return false;
         }
-        for (int i = 0; i < characters.length; ++i) {
+        for (int i = 0; i < charactersLength(); ++i) {
-            if (characters[i] != buffer.charAt(i)) {
+            if (charactersGet(i) != buffer.charAt(i)) {
                 return false;
             }
         }
@@ -191,11 +221,11 @@ public class TString extends TObject implements TSerializable, TComparable<TStri
         if (this == charSeq) {
             return true;
         }
-        if (characters.length != charSeq.length()) {
+        if (charactersLength() != charSeq.length()) {
             return false;
         }
-        for (int i = 0; i < characters.length; ++i) {
+        for (int i = 0; i < charactersLength(); ++i) {
-            if (characters[i] != charSeq.charAt(i)) {
+            if (charactersGet(i) != charSeq.charAt(i)) {
                 return false;
             }
         }
@@ -302,8 +332,8 @@ public class TString extends TObject implements TSerializable, TComparable<TStri
         fromIndex = Math.max(0, fromIndex);
         if (ch < TCharacter.MIN_SUPPLEMENTARY_CODE_POINT) {
             char bmpChar = (char) ch;
-            for (int i = fromIndex; i < characters.length; ++i) {
+            for (int i = fromIndex; i < charactersLength(); ++i) {
-                if (characters[i] == bmpChar) {
+                if (charactersGet(i) == bmpChar) {
                     return i;
                 }
             }
@@ -311,8 +341,8 @@ public class TString extends TObject implements TSerializable, TComparable<TStri
         } else {
             char hi = TCharacter.highSurrogate(ch);
             char lo = TCharacter.lowSurrogate(ch);
-            for (int i = fromIndex; i < characters.length - 1; ++i) {
+            for (int i = fromIndex; i < charactersLength() - 1; ++i) {
-                if (characters[i] == hi && characters[i + 1] == lo) {
+                if (charactersGet(i) == hi && charactersGet(i + 1) == lo) {
                     return i;
                 }
             }
@@ -329,7 +359,7 @@ public class TString extends TObject implements TSerializable, TComparable<TStri
         if (ch < TCharacter.MIN_SUPPLEMENTARY_CODE_POINT) {
             char bmpChar = (char) ch;
             for (int i = fromIndex; i >= 0; --i) {
-                if (characters[i] == bmpChar) {
+                if (charactersGet(i) == bmpChar) {
                     return i;
                 }
             }
@@ -338,7 +368,7 @@ public class TString extends TObject implements TSerializable, TComparable<TStri
             char hi = TCharacter.highSurrogate(ch);
             char lo = TCharacter.lowSurrogate(ch);
             for (int i = fromIndex; i >= 1; --i) {
-                if (characters[i] == lo && characters[i - 1] == hi) {
+                if (charactersGet(i) == lo && charactersGet(i - 1) == hi) {
                     return i - 1;
                 }
             }
@@ -394,12 +424,21 @@ public class TString extends TObject implements TSerializable, TComparable<TStri
         if (beginIndex == endIndex) {
             return EMPTY;
         }
+
+        if (PlatformDetector.isJavaScript()) {
+            var nativeSubstring = substringJS(nativeString(), beginIndex, endIndex);
+            return nativeSubstring != nativeString() ? new TString(nativeSubstring) : this;
+        }
+
         if (beginIndex == 0 && endIndex == length()) {
             return this;
         }
-        return new TString(characters, beginIndex, endIndex - beginIndex);
+        return new TString(fastCharArray(), beginIndex, endIndex - beginIndex);
     }
 
+    @NoSideEffects
+    private native static Object substringJS(Object nativeString, int start, int end);
+
     public TString substring(int beginIndex) {
         return substring(beginIndex, length());
     }
@@ -485,6 +524,10 @@ public class TString extends TObject implements TSerializable, TComparable<TStri
     }
 
     public TString strip() {
+        if (PlatformDetector.isJavaScript()) {
+            var result = stripJS(nativeString());
+            return result != nativeString() ? new TString(result) : this;
+        }
         var lower = 0;
         var upper = length() - 1;
         while (lower <= upper && Character.isWhitespace(charAt(lower))) {
@@ -496,7 +539,13 @@ public class TString extends TObject implements TSerializable, TComparable<TStri
         return substring(lower, upper + 1);
     }
 
+    private static native Object stripJS(Object nativeString);
+
     public TString stripLeading() {
+        if (PlatformDetector.isJavaScript()) {
+            var result = stripLeadingJS(nativeString());
+            return result != nativeString() ? new TString(result) : this;
+        }
         var lower = 0;
         while (lower < length() && Character.isWhitespace(charAt(lower))) {
             ++lower;
@@ -504,7 +553,13 @@ public class TString extends TObject implements TSerializable, TComparable<TStri
         return substring(lower, length());
     }
 
+    private static native Object stripLeadingJS(Object nativeString);
+
     public TString stripTrailing() {
+        if (PlatformDetector.isJavaScript()) {
+            var result = stripTrailingJS(nativeString());
+            return result != nativeString() ? new TString(result) : this;
+        }
         var upper = length() - 1;
         while (0 <= upper && Character.isWhitespace(charAt(upper))) {
             --upper;
@@ -512,15 +567,17 @@ public class TString extends TObject implements TSerializable, TComparable<TStri
         return substring(0, upper + 1);
     }
 
+    private static native Object stripTrailingJS(Object nativeString);
+
     @Override
     public String toString() {
         return (String) (Object) this;
     }
 
     public char[] toCharArray() {
-        char[] array = new char[characters.length];
+        char[] array = new char[charactersLength()];
         for (int i = 0; i < array.length; ++i) {
-            array[i] = characters[i];
+            array[i] = charAt(i);
         }
         return array;
     }
@@ -577,7 +634,10 @@ public class TString extends TObject implements TSerializable, TComparable<TStri
         if (!(other instanceof TString)) {
             return false;
         }
-        TString str = (TString) other;
+        var str = (TString) other;
+        if (PlatformDetector.isJavaScript()) {
+            return nativeString() == str.nativeString();
+        } else {
             if (str.length() != length()) {
                 return false;
             }
@@ -588,6 +648,7 @@ public class TString extends TObject implements TSerializable, TComparable<TStri
             }
             return true;
         }
+    }
 
     public boolean equalsIgnoreCase(TString other) {
         if (this == other) {
@@ -616,7 +677,7 @@ public class TString extends TObject implements TSerializable, TComparable<TStri
     }
 
     public byte[] getBytes(TCharset charset) {
-        TByteBuffer buffer = charset.encode(TCharBuffer.wrap(characters));
+        TByteBuffer buffer = charset.encode(TCharBuffer.wrap(fastCharArray()));
         if (buffer.hasArray() && buffer.position() == 0 && buffer.limit() == buffer.capacity()) {
             return buffer.array();
         } else {
@@ -626,24 +687,33 @@ public class TString extends TObject implements TSerializable, TComparable<TStri
         }
     }
 
+    @NoSideEffects
+    private native char[] fastCharArray();
+
     @Override
     public int hashCode() {
         if (hashCode == 0) {
-            for (char c : characters) {
+            for (var i = 0; i < charactersLength(); ++i) {
-                hashCode = 31 * hashCode + c;
+                hashCode = 31 * hashCode + charactersGet(i);
             }
         }
         return hashCode;
     }
 
     public TString toLowerCase() {
+        if (PlatformDetector.isJavaScript()) {
+            var lowerCase = toLowerCaseJS(nativeString());
+            return lowerCase != nativeString() ? new TString(lowerCase) : this;
+        }
+
         if (isEmpty()) {
             return this;
         }
 
         var hasCharsToTransform = false;
         var hasSurrogates = false;
-        for (var c : characters) {
+        for (var i = 0; i < charactersLength(); ++i) {
+            var c = charactersGet(i);
             if (Character.toLowerCase(c) != c) {
                 hasCharsToTransform = true;
                 break;
@@ -658,24 +728,28 @@ public class TString extends TObject implements TSerializable, TComparable<TStri
         return hasSurrogates ? toLowerCaseCodePoints() : toLowerCaseChars();
     }
 
+    @NoSideEffects
+    private static native Object toLowerCaseJS(Object nativeString);
+
     private TString toLowerCaseChars() {
-        var chars = new char[characters.length];
+        var chars = new char[charactersLength()];
-        for (int i = 0; i < characters.length; ++i) {
+        for (int i = 0; i < charactersLength(); ++i) {
-            chars[i] = TCharacter.toLowerCase(characters[i]);
+            chars[i] = TCharacter.toLowerCase(charactersGet(i));
         }
         return new TString(chars);
     }
 
     private TString toLowerCaseCodePoints() {
-        int[] codePoints = new int[characters.length];
+        int[] codePoints = new int[charactersLength()];
         int codePointCount = 0;
-        for (int i = 0; i < characters.length; ++i) {
+        var length = charactersLength();
-            if (i == characters.length - 1 || !TCharacter.isHighSurrogate(characters[i])
+        for (int i = 0; i < charactersLength(); ++i) {
-                    || !TCharacter.isLowSurrogate(characters[i + 1])) {
+            if (i == length - 1 || !TCharacter.isHighSurrogate(charactersGet(i))
-                codePoints[codePointCount++] = TCharacter.toLowerCase(characters[i]);
+                    || !TCharacter.isLowSurrogate(charactersGet(i + 1))) {
+                codePoints[codePointCount++] = TCharacter.toLowerCase(charactersGet(i));
             } else {
                 codePoints[codePointCount++] = TCharacter.toLowerCase(TCharacter.toCodePoint(
-                        characters[i], characters[i + 1]));
+                        charactersGet(i), charactersGet(i + 1)));
                 ++i;
             }
         }
@@ -687,13 +761,19 @@ public class TString extends TObject implements TSerializable, TComparable<TStri
     }
 
     public TString toUpperCase() {
+        if (PlatformDetector.isJavaScript()) {
+            var upperCase = toUpperCaseJS(nativeString());
+            return upperCase != nativeString() ? new TString(upperCase) : this;
+        }
+
         if (isEmpty()) {
             return this;
         }
 
         var hasCharsToTransform = false;
         var hasSurrogates = false;
-        for (var c : characters) {
+        for (var i = 0; i < charactersLength(); ++i) {
+            var c = charactersGet(i);
             if (Character.toUpperCase(c) != c) {
                 hasCharsToTransform = true;
                 break;
@@ -708,24 +788,27 @@ public class TString extends TObject implements TSerializable, TComparable<TStri
         return hasSurrogates ? toUpperCaseCodePoints() : toUpperCaseChars();
     }
 
+    @NoSideEffects
+    private static native Object toUpperCaseJS(Object nativeString);
+
     private TString toUpperCaseChars() {
-        var chars = new char[characters.length];
+        var chars = new char[charactersLength()];
-        for (int i = 0; i < characters.length; ++i) {
+        for (int i = 0; i < charactersLength(); ++i) {
-            chars[i] = TCharacter.toUpperCase(characters[i]);
+            chars[i] = TCharacter.toUpperCase(charactersGet(i));
         }
         return new TString(chars);
     }
 
     private TString toUpperCaseCodePoints() {
-        int[] codePoints = new int[characters.length];
+        int[] codePoints = new int[charactersLength()];
         int codePointCount = 0;
-        for (int i = 0; i < characters.length; ++i) {
+        for (int i = 0; i < charactersLength(); ++i) {
-            if (i == characters.length - 1 || !TCharacter.isHighSurrogate(characters[i])
+            if (i == charactersLength() - 1 || !TCharacter.isHighSurrogate(charactersGet(i))
-                    || !TCharacter.isLowSurrogate(characters[i + 1])) {
+                    || !TCharacter.isLowSurrogate(charactersGet(i + 1))) {
-                codePoints[codePointCount++] = TCharacter.toUpperCase(characters[i]);
+                codePoints[codePointCount++] = TCharacter.toUpperCase(charactersGet(i));
             } else {
                 codePoints[codePointCount++] = TCharacter.toUpperCase(TCharacter.toCodePoint(
-                        characters[i], characters[i + 1]));
+                        charactersGet(i), charactersGet(i + 1)));
                 ++i;
             }
         }
@@ -736,8 +819,7 @@ public class TString extends TObject implements TSerializable, TComparable<TStri
         return toUpperCase();
     }
 
-    @GeneratedBy(StringNativeGenerator.class)
+    @PluggableDependency(StringNativeDependency.class)
-    @PluggableDependency(StringNativeGenerator.class)
     @NoSideEffects
     public native TString intern();
 
@@ -820,10 +902,10 @@ public class TString extends TObject implements TSerializable, TComparable<TStri
         if (count == 1) {
             return this;
         }
-        if (characters.length == 0 || count == 0) {
+        if (charactersLength() == 0 || count == 0) {
             return EMPTY;
         }
-        var chars = new char[characters.length * count];
+        var chars = new char[charactersLength() * count];
         var j = 0;
         for (int i = 0; i < count; i++) {
             getChars(0, length(), chars, j);

core/src/main/java/org/teavm/backend/javascript/JavaScriptTarget.java

@@ -266,9 +266,8 @@ public class JavaScriptTarget implements TeaVMTarget, TeaVMJavaScriptHost {
         dep.getResult().propagate(dependencyAnalyzer.getType("java.lang.Class"));
         dep.use();
 
-        dep = dependencyAnalyzer.linkMethod(new MethodReference(String.class, "<init>", char[].class, void.class));
+        dep = dependencyAnalyzer.linkMethod(new MethodReference(String.class, "<init>", Object.class, void.class));
         dep.getVariable(0).propagate(stringType);
-        dep.getVariable(1).propagate(dependencyAnalyzer.getType("[C"));
         dep.use();
 
         dependencyAnalyzer.linkField(new FieldReference(String.class.getName(), "characters"));

core/src/main/java/org/teavm/backend/javascript/rendering/Renderer.java

@@ -263,7 +263,8 @@ public class Renderer implements RenderingManager {
                 "$rt_createShortArray", "$rt_createCharArray", "$rt_createIntArray", "$rt_createLongArray",
                 "$rt_createFloatArray", "$rt_createDoubleArray", "$rt_compare",
                 "$rt_castToClass", "$rt_castToInterface", "$rt_equalDoubles",
-                "Long_toNumber", "Long_fromInt", "Long_fromNumber", "Long_create", "Long_ZERO",
+                "$rt_str", "Long_toNumber", "Long_fromInt", "Long_fromNumber", "Long_create", "Long_ZERO",
+                "$rt_intern", "$rt_substring",
                 "Long_hi", "Long_lo");
     }
 

core/src/main/java/org/teavm/backend/javascript/rendering/RuntimeRenderer.java

@@ -73,6 +73,7 @@ public class RuntimeRenderer {
             renderRuntimeThrowableMethods();
             renderRuntimeNullCheck();
             renderRuntimeIntern();
+            renderStringClassInit();
             renderRuntimeThreads();
             renderRuntimeCreateException();
             renderCreateStackTraceElement();
@@ -123,33 +124,21 @@ public class RuntimeRenderer {
     }
 
     private void renderRuntimeString() throws IOException {
-        MethodReference stringCons = new MethodReference(String.class, "<init>", char[].class, void.class);
+        MethodReference stringCons = new MethodReference(String.class, "<init>", Object.class, void.class);
-        writer.append("function $rt_str(str) {").indent().softNewLine();
+        writer.append("function $rt_str(str)").ws().append("{").indent().softNewLine();
         writer.append("if (str === null) {").indent().softNewLine();
         writer.append("return null;").softNewLine();
         writer.outdent().append("}").softNewLine();
-        writer.append("var characters = $rt_createCharArray(str.length);").softNewLine();
+        writer.append("return ").appendInit(stringCons).append("(str);").softNewLine();
-        writer.append("var charsBuffer = characters.data;").softNewLine();
-        writer.append("for (var i = 0; i < str.length; i = (i + 1) | 0) {").indent().softNewLine();
-        writer.append("charsBuffer[i] = str.charCodeAt(i) & 0xFFFF;").softNewLine();
-        writer.outdent().append("}").softNewLine();
-        writer.append("return ").appendInit(stringCons).append("(characters);").softNewLine();
         writer.outdent().append("}").newLine();
     }
 
     private void renderRuntimeUnwrapString() throws IOException {
-        FieldReference stringChars = new FieldReference(STRING_CLASS, "characters");
+        FieldReference stringChars = new FieldReference(STRING_CLASS, "nativeString");
-        writer.append("function $rt_ustr(str) {").indent().softNewLine();
+        writer.append("function $rt_ustr(str)").ws().append("{").indent().softNewLine();
-        writer.append("if (str === null) {").indent().softNewLine();
+        writer.append("return str").ws().append("!==").ws().append("null");
-        writer.append("return null;").softNewLine();
+        writer.ws().append("?").ws().append("str.").appendField(stringChars);
-        writer.outdent().append("}").softNewLine();
+        writer.ws().append(":").ws().append("null").append(";").softNewLine();
-
-        writer.append("var data = str.").appendField(stringChars).append(".data;").softNewLine();
-        writer.append("var result = \"\";").softNewLine();
-        writer.append("for (var i = 0; i < data.length; i = (i + 1) | 0) {").indent().softNewLine();
-        writer.append("result += String.fromCharCode(data[i]);").softNewLine();
-        writer.outdent().append("}").softNewLine();
-        writer.append("return result;").softNewLine();
         writer.outdent().append("}").newLine();
     }
 
@@ -169,17 +158,15 @@ public class RuntimeRenderer {
             writer.outdent().append("}").softNewLine();
         } else {
             renderHandWrittenRuntime("intern.js");
-            writer.append("function $rt_stringHash(s)").ws().append("{").indent().softNewLine();
-            writer.append("return ").appendMethodBody(String.class, "hashCode", int.class)
-                    .append("(s);").softNewLine();
-            writer.outdent().append("}").softNewLine();
-            writer.append("function $rt_stringEquals(a,").ws().append("b)").ws().append("{").indent().softNewLine();
-            writer.append("return ").appendMethodBody(String.class, "equals", Object.class, boolean.class)
-                    .append("(a").ws().append(",b);").softNewLine();
-            writer.outdent().append("}").softNewLine();
         }
     }
 
+    private void renderStringClassInit() throws IOException {
+        writer.append("function $rt_stringClassInit(str)").ws().append("{").indent().softNewLine();
+        writer.appendClassInit("java.lang.String").append("();").softNewLine();
+        writer.outdent().append("}").softNewLine();
+    }
+
     private boolean needInternMethod() {
         ClassReader cls = classSource.get(STRING_CLASS);
         if (cls == null) {

core/src/main/resources/org/teavm/backend/javascript/intern.js

@@ -16,49 +16,34 @@
 "use strict";
 
 var $rt_intern = function() {
-    var table = new Array(100);
+    var map = Object.create(null);
-    var size = 0;
 
-    function get(str) {
+    var get;
-        var hash = $rt_stringHash(str);
+    if (typeof WeakRef !== 'undefined') {
-        var bucket = getBucket(hash);
+        var registry = new FinalizationRegistry(value => {
-        for (var i = 0; i < bucket.length; ++i) {
+            delete map[value];
-            if ($rt_stringEquals(bucket[i], str)) {
+        });
-                return bucket[i];
-            }
-        }
-        bucket.push(str);
-        return str;
-    }
 
-    function getBucket(hash) {
+        get = function(str) {
-        while (true) {
+            var key = $rt_ustr(str);
-            var position = hash % table.length;
+            var ref = map[key];
-            var bucket = table[position];
+            var result = typeof ref !== 'undefined' ? ref.deref() : void 0;
-            if (typeof bucket !== "undefined") {
+            if (typeof result !== 'object') {
-                return bucket;
+                result = str;
+                map[key] = new WeakRef(result);
+                registry.register(result, key);
+            }
+            return result;
         }
-            if (++size / table.length > 0.5) {
-                rehash();
     } else {
-                bucket = [];
+        get = function(str) {
-                table[position] = bucket;
+            var key = $rt_ustr(str);
-                return bucket;
+            var result = map[key];
-            }
+            if (typeof result !== 'object') {
-        }
+                result = str;
-    }
+                map[key] = result;
-
-    function rehash() {
-        var old = table;
-        table = new Array(table.length * 2);
-        size = 0;
-        for (var i = 0; i < old.length; ++i) {
-            var bucket = old[i];
-            if (typeof bucket !== "undefined") {
-                for (var j = 0; j < bucket.length; ++j) {
-                    get(bucket[j]);
-                }
             }
+            return result;
         }
     }
 

core/src/main/resources/org/teavm/backend/javascript/runtime.js

@@ -644,6 +644,7 @@ function $rt_mainStarter(f) {
 }
 var $rt_stringPool_instance;
 function $rt_stringPool(strings) {
+    $rt_stringClassInit();
     $rt_stringPool_instance = new Array(strings.length);
     for (var i = 0; i < strings.length; ++i) {
         $rt_stringPool_instance[i] = $rt_intern($rt_str(strings[i]));
@@ -938,3 +939,35 @@ function $rt_classWithoutFields(superclass) {
         superclass.call(this);
     };
 }
+function $rt_charArrayToString(array, offset, count) {
+    var result = "";
+    var limit = offset + count;
+    for (var i = offset; i < limit; i = (i + 1024) | 0) {
+        var next = Math.min(limit, (i + 1024) | 0);
+        result += String.fromCharCode.apply(null, array.subarray(i, next));
+    }
+    return result;
+}
+function $rt_fullArrayToString(array) {
+    return $rt_charArrayToString(array, 0, array.length);
+}
+function $rt_stringToCharArray(string, begin, dst, dstBegin, count) {
+    for (var i = 0; i < count; i = (i + 1) | 0) {
+        dst[dstBegin + i] = string.charCodeAt(begin + i);
+    }
+}
+function $rt_fastStringToCharArray(string) {
+    var array = new Uint16Array(string.length);
+    for (var i = 0; i < array.length; ++i) {
+        array[i] = string.charCodeAt(i);
+    }
+    return $rt_createNumericArray($rt_charcls(), array);
+}
+function $rt_substring(string, start, end) {
+    if (start === 0 && end === string.length) {
+        return string;
+    }
+    var result = start.substring(start, end - 1) + start.substring(end - 1, end);
+    $rt_substringSink = ($rt_substringSink + result.charCodeAt(result.length - 1)) | 0;
+}
+var $rt_substringSink = 0;

html4j/src/main/java/org/teavm/html4j/JavaScriptConvGenerator.java

@@ -125,7 +125,7 @@ public class JavaScriptConvGenerator implements Generator {
 
         writer.outdent().append("} else if (" + type + " === ").appendClass("java.lang.String")
                 .append(") {").indent().softNewLine();
-        writer.append("return $rt_str(" + obj + ");").softNewLine();
+        writer.append("return ").appendFunction("$rt_str").append("(").append(obj).append(");").softNewLine();
 
         writer.outdent().append("} else if (" + type + " === ").appendClass("java.lang.Boolean")
                 .append(") {").indent().softNewLine();
@@ -179,7 +179,7 @@ public class JavaScriptConvGenerator implements Generator {
         writer.append("return arr;").softNewLine();
 
         writer.outdent().append("} else if (typeof " + obj + " === 'string') {").indent().softNewLine();
-        writer.append("return $rt_str(" + obj + ");").softNewLine();
+        writer.append("return ").appendFunction("$rt_str").append("(" + obj + ");").softNewLine();
 
         writer.outdent().append("} else if (typeof " + obj + " === 'number') {").indent().softNewLine();
         writer.append("if ((" + obj + "|0) === " + obj + ") {").indent().softNewLine();

jso/impl/src/main/java/org/teavm/jso/impl/JSNativeGenerator.java

@@ -166,7 +166,7 @@ public class JSNativeGenerator implements Injector, DependencyPlugin, Generator
                 }
                 break;
             case "unwrapString":
-                writer.append("$rt_str(");
+                writer.appendFunction("$rt_str").append("(");
                 context.writeExpr(context.getArgument(0), Precedence.min());
                 writer.append(")");
                 break;

platform/src/main/java/org/teavm/platform/plugin/ResourceAccessorInjector.java

@@ -87,7 +87,7 @@ class ResourceAccessorInjector implements Injector {
                 context.getWriter().append('(');
                 context.writeExpr(context.getArgument(0));
                 context.getWriter().ws().append("!==").ws().append("null").ws().append("?").ws();
-                context.getWriter().append("$rt_str(");
+                context.getWriter().appendFunction("$rt_str").append("(");
                 context.writeExpr(context.getArgument(0));
                 context.getWriter().append(")").ws().append(':').ws().append("null)");
                 break;

tests/src/test/java/org/teavm/incremental/EntryPointGenerator.java

@@ -26,7 +26,6 @@ public class EntryPointGenerator implements Injector {
     public void generate(InjectorContext context, MethodReference methodRef) throws IOException {
         context.getWriter().append("main.result = (");
         context.writeExpr(context.getArgument(0));
-        context.getWriter().append(").").appendField(new FieldReference("java.lang.String", "characters"));
+        context.getWriter().append(").").appendField(new FieldReference("java.lang.String", "nativeString"));
-        context.getWriter().append(".data");
     }
 }

tests/src/test/java/org/teavm/incremental/IncrementalTest.java

@@ -40,7 +40,6 @@ import org.mozilla.javascript.ScriptRuntime;
 import org.mozilla.javascript.Scriptable;
 import org.mozilla.javascript.ScriptableObject;
 import org.mozilla.javascript.Undefined;
-import org.mozilla.javascript.typedarrays.NativeUint16Array;
 import org.teavm.ast.AsyncMethodNode;
 import org.teavm.backend.javascript.JavaScriptTarget;
 import org.teavm.cache.AlwaysStaleCacheStatus;
@@ -169,12 +168,7 @@ public class IncrementalTest {
         Function main = (Function) scope.get("main", scope);
         ScriptRuntime.doTopCall(main, rhinoContext, scope, scope,
                 new Object[] { new NativeArray(0), Undefined.instance });
-        NativeUint16Array jsChars = (NativeUint16Array) main.get("result", main);
+        return main.get("result", main).toString();
-        char[] chars = new char[jsChars.getArrayLength()];
-        for (int i = 0; i < chars.length; ++i) {
-            chars[i] = (char) jsChars.get(i).intValue();
-        }
-        return new String(chars);
     }
 
     private static String getSimpleName(String name) {