Various code size optimizations

1. Generate 'a' for 'this' instead of '$t'
2. Fix frequency-based identifier optimization
3. Generate less code in <clinit> callers
4. Generate one-letter identifier in most of constructors
   (instead of $r)
5. Use $ and _ chars in identifiers

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

@@ -318,6 +318,7 @@ public class JavaScriptTarget implements TeaVMTarget, TeaVMJavaScriptHost {
             }
             int start = sourceWriter.getOffset();
             sourceWriter.append("\"use strict\";").newLine();
+            renderer.prepare(clsNodes);
             renderer.renderRuntime();
             renderer.render(clsNodes);
             renderer.renderStringPool();

core/src/main/java/org/teavm/backend/javascript/codegen/MinifyingAliasProvider.java

@@ -83,7 +83,7 @@ public class MinifyingAliasProvider implements AliasProvider {
     public String getClassInitAlias(String className) {
         String result;
         do {
-            result =  RenderingUtil.indexToId(lastSuffix++, startLetters);
+            result = RenderingUtil.indexToId(lastSuffix++, startLetters);
         } while (!usedAliases.add(result) || RenderingUtil.KEYWORDS.contains(result));
         return result;
     }

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

@@ -100,6 +100,11 @@ class NameFrequencyEstimator extends RecursiveVisitor implements MethodNodeVisit
                 consumer.consumeFunction("$rt_resuming");
                 consumer.consumeFunction("$rt_invalidPointer");
             }
+            method.acceptVisitor(this);
+        }
+
+        if (clinit != null) {
+            consumer.consumeFunction("$rt_eraseClinit");
         }
 
         // Metadata

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

@@ -295,7 +295,7 @@ public class Renderer implements RenderingManager {
     private void renderRuntimeAliases() throws IOException {
         String[] names = { "$rt_throw", "$rt_compare", "$rt_nullCheck", "$rt_cls", "$rt_createArray",
                 "$rt_isInstance", "$rt_nativeThread", "$rt_suspending", "$rt_resuming", "$rt_invalidPointer",
-                "$rt_s" };
+                "$rt_s", "$rt_eraseClinit" };
         boolean first = true;
         for (String name : names) {
             if (!first) {
@@ -307,7 +307,7 @@ public class Renderer implements RenderingManager {
         writer.newLine();
     }
 
-    public void render(List<ClassNode> classes) throws RenderingException {
+    public void prepare(List<ClassNode> classes) {
         if (minifying) {
             NamingOrderer orderer = new NamingOrderer();
             NameFrequencyEstimator estimator = new NameFrequencyEstimator(orderer, classSource, asyncMethods,
@@ -317,7 +317,9 @@ public class Renderer implements RenderingManager {
             }
             orderer.apply(naming);
         }
+    }
 
+    public void render(List<ClassNode> classes) throws RenderingException {
         if (minifying) {
             try {
                 renderRuntimeAliases();
@@ -484,8 +486,8 @@ public class Renderer implements RenderingManager {
 
     private void renderEraseClinit(ClassNode cls) throws IOException {
         writer.append(naming.getNameForClassInit(cls.getName())).ws().append("=").ws()
-                .appendClass(cls.getName()).append(".$clinit").ws().append("=").ws()
+                .appendFunction("$rt_eraseClinit").append("(")
-                .append("function(){};").newLine();
+                .appendClass(cls.getName()).append(");").softNewLine();
     }
 
     private void renderClassMetadata(List<ClassNode> classes) {
@@ -713,22 +715,24 @@ public class Renderer implements RenderingManager {
         MethodReference ref = method.getReference();
         debugEmitter.emitMethod(ref.getDescriptor());
         writer.append("function ").append(naming.getNameForInit(ref)).append("(");
-        for (int i = 1; i <= ref.parameterCount(); ++i) {
+        for (int i = 0; i < ref.parameterCount(); ++i) {
-            if (i > 1) {
+            if (i > 0) {
                 writer.append(",").ws();
             }
             writer.append(variableNameForInitializer(i));
         }
         writer.append(")").ws().append("{").softNewLine().indent();
-        writer.append("var $r").ws().append("=").ws().append("new ").appendClass(
+
+        String instanceName = variableNameForInitializer(ref.parameterCount());
+        writer.append("var " + instanceName).ws().append("=").ws().append("new ").appendClass(
                 ref.getClassName()).append("();").softNewLine();
-        writer.append(naming.getFullNameFor(ref)).append("($r");
+        writer.append(naming.getFullNameFor(ref)).append("(" + instanceName);
-        for (int i = 1; i <= ref.parameterCount(); ++i) {
+        for (int i = 0; i < ref.parameterCount(); ++i) {
             writer.append(",").ws();
             writer.append(variableNameForInitializer(i));
         }
         writer.append(");").softNewLine();
-        writer.append("return $r;").softNewLine();
+        writer.append("return " + instanceName + ";").softNewLine();
         writer.outdent().append("}").newLine();
         debugEmitter.emitMethod(null);
     }

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

@@ -27,7 +27,7 @@ public final class RenderingUtil {
             "super", "switch", "this", "throw", "try", "typeof", "var", "void", "while", "with", "yield",
             "NaN")));
     public static final String VARIABLE_START_CHARS = "abcdefghijklmnopqrstuvwxyz";
-    public static final String VARIABLE_PART_CHARS = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
+    public static final String VARIABLE_PART_CHARS = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789$_";
 
     private RenderingUtil() {
     }

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

@@ -462,10 +462,6 @@ public class StatementRenderer implements ExprVisitor, StatementVisitor {
     }
 
     private String generateVariableName(int index) {
-        if (index == 0 && minifying) {
-            return "$t";
-        }
-
         if (!minifying) {
             VariableNode variable = index < currentMethod.getVariables().size()
                     ? currentMethod.getVariables().get(index)
@@ -484,7 +480,7 @@ public class StatementRenderer implements ExprVisitor, StatementVisitor {
                 return "var$" + index;
             }
         } else {
-            return RenderingUtil.indexToId(--index);
+            return RenderingUtil.indexToId(index);
         }
     }
 

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

@@ -520,6 +520,9 @@ function $rt_stringPool(strings) {
 function $rt_s(index) {
     return $rt_stringPool_instance[index];
 }
+function $rt_eraseClinit(target) {
+    return target.$clinit = function() {};
+}
 function TeaVMThread(runner) {
     this.status = 3;
     this.stack = [];