/***
* ASM examples: examples showing how ASM can be used
* Copyright (c) 2000,2002,2003 INRIA, France Telecom
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* 3. Neither the name of the copyright holders nor the names of its
* contributors may be used to endorse or promote products derived from
* this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
* LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
* THE POSSIBILITY OF SUCH DAMAGE.
*/
import org.objectweb.asm.ClassWriter;
import org.objectweb.asm.CodeVisitor;
import org.objectweb.asm.Constants;
import org.objectweb.asm.Label;
import java.io.FileOutputStream;
/**
* @author Eric Bruneton
*/
public class Compile extends ClassLoader {
public static void main (String[] args) throws Exception {
// creates the expression tree corresponding to
// exp(i) = i > 3 && 6 > i
Exp exp = new And(new GT(new Var(0), new Cst(3)),
new GT(new Cst(6), new Var(0)));
// compiles this expression into an Expression class
Compile main = new Compile();
byte[] b = exp.compile("Example");
FileOutputStream fos = new FileOutputStream("Example.class");
fos.write(b);
fos.close();
Class expClass = main.defineClass("Example", b, 0, b.length);
// instantiates this compiled expression class...
Expression iexp = (Expression)expClass.newInstance();
// ... and uses it to evaluate exp(0) to exp(9)
for (int i = 0; i < 10; ++i) {
boolean val = iexp.eval(i, 0) == 1;
System.out.println(i + " > 3 && " + i + " < 6 = " + val);
}
}
}
/**
* An abstract expression.
*
* @author Eric Bruneton
*/
abstract class Exp implements Constants {
/*
* Returns the byte code of an Expression class corresponding to this
* expression.
*/
byte[] compile (String name) {
// class header
String[] itfs = {Expression.class.getName()};
ClassWriter cw = new ClassWriter(true);
cw.visit(V1_1, ACC_PUBLIC, name, "java/lang/Object", itfs, null);
// default public constructor
CodeVisitor mw = cw.visitMethod(ACC_PUBLIC, "<init>", "()V", null, null);
mw.visitVarInsn(ALOAD, 0);
mw.visitMethodInsn(
INVOKESPECIAL,
"java/lang/Object", "<init>", "()V");
mw.visitInsn(RETURN);
mw.visitMaxs(1, 1);
// eval method
mw = cw.visitMethod(ACC_PUBLIC, "eval", "(II)I", null, null);
compile(mw);
mw.visitInsn(IRETURN);
// max stack and max locals automatically computed
mw.visitMaxs(0, 0);
return cw.toByteArray();
}
/*
* Compile this expression. This method must append to the given code
* writer the byte code that evaluates and pushes on the stack the
* value of this expression.
*/
abstract void compile (CodeVisitor mw);
}
/**
* A constant expression.
*/
class Cst extends Exp {
int value;
Cst (int value) {
this.value = value;
}
void compile (CodeVisitor mw) {
// pushes the constant's value onto the stack
mw.visitLdcInsn(new Integer(value));
}
}
/**
* A variable reference expression.
*/
class Var extends Exp {
int index;
Var (int index) {
this.index = index + 1;
}
void compile (CodeVisitor mb) {
// pushes the 'index' local variable onto the stack
mb.visitVarInsn(ILOAD, index);
}
}
/**
* An abstract binary expression.
*/
abstract class BinaryExp extends Exp {
Exp e1;
Exp e2;
BinaryExp (Exp e1, Exp e2) {
this.e1 = e1;
this.e2 = e2;
}
}
/**
* An addition expression.
*/
class Add extends BinaryExp {
Add (Exp e1, Exp e2) {
super(e1, e2);
}
void compile (CodeVisitor mw) {
// compiles e1, e2, and adds an instruction to add the two values
e1.compile(mw);
e2.compile(mw);
mw.visitInsn(IADD);
}
}
/**
* A multiplication expression.
*/
class Mul extends BinaryExp {
Mul (Exp e1, Exp e2) {
super(e1, e2);
}
void compile (CodeVisitor mb) {
// compiles e1, e2, and adds an instruction to multiply the two values
e1.compile(mb);
e2.compile(mb);
mb.visitInsn(IMUL);
}
}
/**
* A "greater than" expression.
*/
class GT extends BinaryExp {
GT (Exp e1, Exp e2) {
super(e1, e2);
}
void compile (CodeVisitor mw) {
// compiles e1, e2, and adds the instructions to compare the two values
e1.compile(mw);
e2.compile(mw);
Label iftrue = new Label();
Label end = new Label();
mw.visitJumpInsn(IF_ICMPGT, iftrue);
// case where e1 <= e2 : pushes false and jump to "end"
mw.visitInsn(ICONST_0);
mw.visitJumpInsn(GOTO, end);
// case where e1 > e2 : pushes true
mw.visitLabel(iftrue);
mw.visitInsn(ICONST_1);
mw.visitLabel(end);
}
}
/**
* A logical "and" expression.
*/
class And extends BinaryExp {
And (Exp e1, Exp e2) {
super(e1, e2);
}
void compile (CodeVisitor mw) {
// compiles e1
e1.compile(mw);
// tests if e1 is false
mw.visitInsn(DUP);
Label end = new Label();
mw.visitJumpInsn(IFEQ, end);
// case where e1 is true : e1 && e2 is equal to e2
mw.visitInsn(POP);
e2.compile(mw);
// if e1 is false, e1 && e2 is equal to e1:
// we jump directly to this label, without evaluating e2
mw.visitLabel(end);
}
}
/**
* A logical "or" expression.
*/
class Or extends BinaryExp {
Or (Exp e1, Exp e2) {
super(e1, e2);
}
void compile (CodeVisitor mw) {
// compiles e1
e1.compile(mw);
// tests if e1 is true
mw.visitInsn(DUP);
Label end = new Label();
mw.visitJumpInsn(IFNE, end);
// case where e1 is false : e1 || e2 is equal to e2
mw.visitInsn(POP);
e2.compile(mw);
// if e1 is true, e1 || e2 is equal to e1:
// we jump directly to this label, without evaluating e2
mw.visitLabel(end);
}
}
/**
* A logical "not" expression.
*/
class Not extends Exp {
Exp e;
Not (Exp e) {
this.e = e;
}
void compile (CodeVisitor mw) {
// computes !e1 by evaluating 1 - e1
mw.visitInsn(ICONST_1);
e.compile(mw);
mw.visitInsn(ISUB);
}
}