ZeroTransformer.java

/*
 * dex2jar - Tools to work with android .dex and java .class files
 * Copyright (c) 2009-2014 Panxiaobo
 *
 * 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 com.googlecode.dex2jar.ir.ts;

import com.googlecode.dex2jar.ir.IrMethod;
import com.googlecode.dex2jar.ir.expr.Constant;
import com.googlecode.dex2jar.ir.expr.Exprs;
import com.googlecode.dex2jar.ir.expr.Local;
import com.googlecode.dex2jar.ir.expr.Value;
import com.googlecode.dex2jar.ir.stmt.AssignStmt;
import com.googlecode.dex2jar.ir.stmt.LabelStmt;
import com.googlecode.dex2jar.ir.stmt.Stmt;
import com.googlecode.dex2jar.ir.stmt.Stmts;

import java.util.ArrayList;
import java.util.List;

/**
 * dex mix use as integer 0 and object null. the following code is validate in dex, but invalidate in .class
 * 
 * <pre>
 *     a=0
 *     if x>0 goto L1
 *     L2: [b=phi(a,c)]
 *     useAsObject(b);
 *     c=getAnotherObject();
 *     goto L2:
 *     L1: [d=phi(a,e)]
 *     useAsInt(d);
 *     e=123
 *     goto L1:
 * </pre>
 * 
 * we transform the code to
 * 
 * <pre>
 *     a1=0
 *     a=0
 *     if x>0 goto L1
 *     a2=0
 *     L2: [b=phi(a1,c)]
 *     useAsObject(b);
 *     c=getAnotherObject();
 *     goto L2:
 *     L1: [d=phi(a,e)]
 *     useAsInt(d);
 *     e=123
 *     goto L1:
 * </pre>
 */
public class ZeroTransformer extends StatedTransformer {

    @Override
    public boolean transformReportChanged(IrMethod method) {
        boolean changed = false;
        List<AssignStmt> assignStmtList = new ArrayList<>();

        for (Stmt p = method.stmts.getFirst(); p != null; p = p.getNext()) {
            if (p.st == Stmt.ST.ASSIGN) {
                AssignStmt as = (AssignStmt) p;
                if (as.getOp1().vt == Value.VT.LOCAL && as.getOp2().vt == Value.VT.CONSTANT) {
                    Constant cst = (Constant) as.getOp2();
                    Object value = cst.value;
                    if (value instanceof Number && !((value instanceof Long) || (value instanceof Double))) {
                        int v = ((Number) value).intValue();
                        if (v == 0 || v == 1) {
                            assignStmtList.add(as);
                        }
                    }
                }
            }
        }
        if (assignStmtList.size() == 0) {
            return false;
        }
        List<LabelStmt> phiLabels = method.phiLabels;
        if (phiLabels != null) {
            for (AssignStmt as : assignStmtList) {
                Local local = (Local) as.getOp1();
                boolean first = true;
                for (LabelStmt labelStmt : phiLabels) {
                    for (AssignStmt phi : labelStmt.phis) {
                        Value[] vs = phi.getOp2().getOps();
                        for (int i = 0; i < vs.length; i++) {
                            Value v = vs[i];
                            if (v == local) {
                                if (first) {
                                    first = false;
                                } else {
                                    Local nLocal = Exprs.nLocal(-1);
                                    method.locals.add(nLocal);
                                    changed = true;
                                    method.stmts.insertBefore(as, Stmts.nAssign(nLocal, as.getOp2().clone()));
                                    vs[i] = nLocal;
                                }
                            }
                        }
                    }
                }
            }
        }
        return changed;
    }
}