Using ASM for control flow : example from asmifier

NestedIfs.java

public class NestedIfs {
    public static int run(int a, int b){
	int res= 0;
	if( (a-b) == 0){
	    int c= a+b;
	    if(c != 0){
		c= 5;
	    }else{
		c= 2;
	    }
	    res= -c;
	}else{
	    res= 1;
	}
	return res;
    }
}

NestedIfsDump.java

import java.util.*;
import org.objectweb.asm.*;
import org.objectweb.asm.attrs.*;
public class NestedIfsDump implements Opcodes {

    public static byte[] dump () throws Exception {

	ClassWriter cw = new ClassWriter(0);
	FieldVisitor fv;
	MethodVisitor mv;
	AnnotationVisitor av0;

	cw.visit(52, ACC_PUBLIC + ACC_SUPER, "NestedIfs", null, "java/lang/Object", null);

	{
	    mv = cw.visitMethod(ACC_PUBLIC, "<init>", "()V", null, null);
	    mv.visitCode();
	    mv.visitVarInsn(ALOAD, 0);
	    mv.visitMethodInsn(INVOKESPECIAL, "java/lang/Object", "<init>", "()V", false);
	    mv.visitInsn(RETURN);
	    mv.visitMaxs(1, 1);
	    mv.visitEnd();
	}
	{
	    mv = cw.visitMethod(ACC_PUBLIC + ACC_STATIC, "run", "(II)I", null, null);
	    mv.visitCode();
	    mv.visitInsn(ICONST_0);
	    mv.visitVarInsn(ISTORE, 2);
	    mv.visitVarInsn(ILOAD, 0);
	    mv.visitVarInsn(ILOAD, 1);
	    mv.visitInsn(ISUB);
	    Label l0 = new Label();
	    mv.visitJumpInsn(IFNE, l0);
	    mv.visitVarInsn(ILOAD, 0);
	    mv.visitVarInsn(ILOAD, 1);
	    mv.visitInsn(IADD);
	    mv.visitVarInsn(ISTORE, 3);
	    mv.visitVarInsn(ILOAD, 3);
	    Label l1 = new Label();
	    mv.visitJumpInsn(IFEQ, l1);
	    mv.visitInsn(ICONST_5);
	    mv.visitVarInsn(ISTORE, 3);
	    Label l2 = new Label();
	    mv.visitJumpInsn(GOTO, l2);
	    mv.visitLabel(l1);
	    mv.visitFrame(Opcodes.F_APPEND,2, new Object[] {Opcodes.INTEGER, Opcodes.INTEGER}, 0, null);
	    mv.visitInsn(ICONST_2);
	    mv.visitVarInsn(ISTORE, 3);
	    mv.visitLabel(l2);
	    mv.visitFrame(Opcodes.F_SAME, 0, null, 0, null);
	    mv.visitVarInsn(ILOAD, 3);
	    mv.visitInsn(INEG);
	    mv.visitVarInsn(ISTORE, 2);
	    Label l3 = new Label();
	    mv.visitJumpInsn(GOTO, l3);
	    mv.visitLabel(l0);
	    mv.visitFrame(Opcodes.F_CHOP,1, null, 0, null);
	    mv.visitInsn(ICONST_1);
	    mv.visitVarInsn(ISTORE, 2);
	    mv.visitLabel(l3);
	    mv.visitFrame(Opcodes.F_SAME, 0, null, 0, null);
	    mv.visitVarInsn(ILOAD, 2);
	    mv.visitInsn(IRETURN);
	    mv.visitMaxs(2, 4);
	    mv.visitEnd();
	}
	cw.visitEnd();

	return cw.toByteArray();
    }
}

TestLoop.java

public class TestLoop{
    public static int run(int i){
	int res;
	if(i !=0){
	    res= i;
	}else{
	    res= -i;
	}
	return res;
    }
}

TestLoopDump.java

import java.util.*;
import org.objectweb.asm.*;
import org.objectweb.asm.attrs.*;
public class TestLoopDump implements Opcodes {

    public static byte[] dump () throws Exception {

	ClassWriter cw = new ClassWriter(0);
	FieldVisitor fv;
	MethodVisitor mv;
	AnnotationVisitor av0;

	cw.visit(52, ACC_PUBLIC + ACC_SUPER, "TestLoop", null, "java/lang/Object", null);

	{
	    mv = cw.visitMethod(ACC_PUBLIC, "<init>", "()V", null, null);
	    mv.visitCode();
	    mv.visitVarInsn(ALOAD, 0);
	    mv.visitMethodInsn(INVOKESPECIAL, "java/lang/Object", "<init>", "()V", false);
	    mv.visitInsn(RETURN);
	    mv.visitMaxs(1, 1);
	    mv.visitEnd();
	}
	{
	    mv = cw.visitMethod(ACC_PUBLIC + ACC_STATIC, "run", "(I)I", null, null);
	    mv.visitCode();
	    mv.visitVarInsn(ILOAD, 0);
	    Label l0 = new Label();
	    mv.visitJumpInsn(IFEQ, l0);
	    mv.visitVarInsn(ILOAD, 0);
	    mv.visitVarInsn(ISTORE, 1);
	    Label l1 = new Label();
	    mv.visitJumpInsn(GOTO, l1);
	    mv.visitLabel(l0);
	    mv.visitFrame(Opcodes.F_SAME, 0, null, 0, null);
	    mv.visitVarInsn(ILOAD, 0);
	    mv.visitInsn(INEG);
	    mv.visitVarInsn(ISTORE, 1);
	    mv.visitLabel(l1);
	    mv.visitFrame(Opcodes.F_APPEND,1, new Object[] {Opcodes.INTEGER}, 0, null);
	    mv.visitVarInsn(ILOAD, 1);
	    mv.visitInsn(IRETURN);
	    mv.visitMaxs(1, 2);
	    mv.visitEnd();
	}
	cw.visitEnd();

	return cw.toByteArray();
    }
}