String concatenation optimization.

src/core/org/luaj/vm2/Buffer.java

@@ -45,30 +45,34 @@ public final class Buffer {
 		return LuaString.valueOf(bytes, 0, length).tojstring();
 	}
 	
-	public final void append( byte b ) {
+	public final Buffer append( byte b ) {
 		ensureCapacity( length + 1 );
 		bytes[ length++ ] = b;
+		return this;
 	}
 	
-	public final void append( LuaValue val ) {
+	public final Buffer append( LuaValue val ) {
 		if ( ! val.isstring() ) 
 			val.error("attempt to concatenate a '"+val.typename()+"' value");
 		append( val.strvalue() );
+		return this;
 	}
 	
-	public final void append( LuaString str ) {
+	public final Buffer append( LuaString str ) {
 		final int alen = str.length();
 		ensureCapacity( length + alen );
 		str.copyInto( 0, bytes, length, alen );
 		length += alen;
+		return this;
 	}
 	
-	public final void append( String str ) {
+	public final Buffer append( String str ) {
 		char[] chars = str.toCharArray();
 		final int alen = LuaString.lengthAsUtf8( chars );
 		ensureCapacity( length + alen );
 		LuaString.encodeToUtf8( chars, bytes, length );
 		length += alen;
+		return this;
 	}
 	
 	public final void setLength( int length ) {

src/jse/org/luaj/vm2/lua2java/JavaCodeGen.java

@@ -533,11 +533,25 @@ public class JavaCodeGen {
 			case Lua.OP_LE: out(evalLuaValue(exp.lhs)+".lteq("+evalNumber(exp.rhs)+")"); return;
 			case Lua.OP_EQ: out(evalLuaValue(exp.lhs)+".eq("+evalLuaValue(exp.rhs)+")"); return;
 			case Lua.OP_NEQ: out(evalLuaValue(exp.lhs)+".neq("+evalLuaValue(exp.rhs)+")"); return;
-			case Lua.OP_CONCAT: out(evalLuaValue(exp.lhs)+".concat("+evalLuaValue(exp.rhs)+")"); return;
+			case Lua.OP_CONCAT: 
+				if ( isConcatExp(exp.rhs) ) {
+					out( "new Buffer().append("+evalLuaValue(exp.lhs)+")" );
+					Exp e = exp.rhs;
+					for ( ; isConcatExp(e); e=((BinopExp)e).rhs ) 
+						out( ".append("+evalLuaValue(((BinopExp)e).lhs)+")" );
+					out( ".append("+evalLuaValue(e)+")" );
+					out( ".tostring()" );
+				} else
+					out(evalLuaValue(exp.lhs)+".concat("+evalLuaValue(exp.rhs)+")"); 
+				return;
 			default: throw new IllegalStateException("unknown bin op:"+exp.op);
 			}
 		}
 
+		private boolean isConcatExp(Exp e) {
+			return (e instanceof BinopExp) && (((BinopExp)e).op == Lua.OP_CONCAT);
+		}
+		
 		public void visit(UnopExp exp) {
 			exp.rhs.accept(this);
 			switch ( exp.op ) {