google/dexmaker/Code.java

/*
 * Copyright (C) 2011 The Android Open Source Project
 *
 * 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.google.dexmaker;

import com.android.dx.rop.code.BasicBlockList;
import com.android.dx.rop.code.Insn;
import com.android.dx.rop.code.PlainCstInsn;
import com.android.dx.rop.code.PlainInsn;
import com.android.dx.rop.code.RegisterSpecList;
import com.android.dx.rop.code.Rop;
import static com.android.dx.rop.code.Rop.BRANCH_GOTO;
import static com.android.dx.rop.code.Rop.BRANCH_NONE;
import static com.android.dx.rop.code.Rop.BRANCH_RETURN;
import com.android.dx.rop.code.Rops;
import com.android.dx.rop.code.SourcePosition;
import com.android.dx.rop.code.ThrowingCstInsn;
import com.android.dx.rop.code.ThrowingInsn;
import com.android.dx.rop.cst.CstInteger;
import com.android.dx.rop.type.StdTypeList;
import static com.android.dx.rop.type.Type.BT_BYTE;
import static com.android.dx.rop.type.Type.BT_CHAR;
import static com.android.dx.rop.type.Type.BT_INT;
import static com.android.dx.rop.type.Type.BT_SHORT;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Iterator;
import java.util.List;

/**
 * Builds a sequence of instructions.
 *
 * <h3>Locals</h3>
 * All data manipulation takes place in local variables. Each parameter gets its
 * own local by default; access these using {@link #getParameter}. Non-static
 * methods and constructors also have a {@code this} parameter; it's available
 * as {@link #getThis}. Allocate a new local variable using {@link #newLocal},
 * and assign a default value to it with {@link #loadConstant}. Every local
 * variable has a fixed type. This is either a primitive type (of any size) or a
 * reference type. This class emits instructions appropriate to the types they
 * operate on. Not all operations are local on all types; attempting to emit
 * such an operation will fail with an unchecked exception.
 *
 * <h3>Math and Bit Operations</h3>
 * Transform a single value into another related value using {@link
 * #op(UnaryOp,Local,Local)}. Transform two values into a third value using
 * {@link #op(BinaryOp,Local,Local,Local)}. In either overload the first {@code
 * Local} parameter is where the result will be sent; the other {@code Local}
 * parameters are the inputs.
 *
 * <h3>Comparisons</h3>
 * There are three different comparison operations each with different
 * constraints:
 * <ul>
 *     <li>{@link #compareLongs(Local,Local,Local)} compares two locals each
 *         containing a {@code long} primitive. This is the only operation that
 *         can compare longs. The result of the comparison is written to another
 *         {@code int} local.</li>
 *     <li>{@link #compareFloatingPoint(Local,Local,Local,int)} compares two
 *         locals; both {@code float} primitives or both {@code double}
 *         primitives. This is the only operation that can compare floating
 *         point values. This comparison takes an extra parameter that sets
 *         the desired result if either parameter is {@code NaN}. The result of
 *         the comparison is wrtten to another {@code int} local.
 *     <li>{@link #compare(Comparison,Label,Local,Local)} compares two locals.
 *         The {@link Comparison#EQ} and {@link Comparison#NE} options compare
 *         either {@code int} primitives or references. The other options
 *         compare only {@code int} primitives. This comparison takes a {@link
 *         Label} that will be jumped to if the comparison is true. If the
 *         comparison is false the next instruction in sequence will be
 *         executed.
 * </ul>
 * There's no single operation to compare longs and jump, or to compare ints and
 * store the result in a local. Accomplish these goals by chaining multiple
 * operations together.
 *
 * <h3>Branches, Labels and Returns</h3>
 * Basic control flow is expressed using jumps and labels. Each label must be
 * marked exactly once and may be jumped to any number of times. Create a label
 * using its constructor: {@code new Label()}, and mark it using {@link #mark}.
 * All jumps to a label will execute instructions starting from that label. You
 * can jump to a label that hasn't yet been marked (jumping forward) or to a
 * label that has already been marked (jumping backward). Jump unconditionally
 * with {@link #jump} or conditionally based on a comparison using {@link
 * #compare(Comparison,Label,Local,Local)}.
 *
 * <p>Most methods should contain either a return instruction. Void methods
 * should use {@link #returnVoid}; non-void methods should use {@link
 * #returnValue} with a local whose return type matches the method's return
 * type. Constructors are considered void methods and should call {@link
 * #returnVoid()}. Methods may make multiple returns. Methods containing no
 * return statements must either loop infinitely or throw unconditionally; it is
 * not legal to end a sequence of instructions without a jump, return or throw.
 *
 * <h3>Throwing and Catching</h3>
 * This API uses labels to handle thrown exceptions, errors and throwables. Call
 * {@link #addCatchClause} to register the target label and throwable class. All
 * statements that follow will jump to that catch clause if they throw a {@link
 * Throwable} assignable to that type. Use {@link #removeCatchClause} to
 * unregister the throwable class.
 *
 * <p>Throw an throwable by first assigning it to a local and then calling
 * {@link #throwValue}. Control flow will jump to the nearest label assigned to
 * a type assignable to the thrown type. In this context, "nearest" means the
 * label requiring the fewest stack frames to be popped.
 *
 * <h3>Calling methods</h3>
 * A method's caller must know its return type, name, parameters, and invoke
 * kind. Lookup a method on a type using {@link TypeId#getMethod}. This is more
 * onerous than Java language invokes, which can infer the target method using
 * the target object and parameters. There are four invoke kinds:
 * <ul>
 *     <li>{@link #invokeStatic} is used for static methods.</li>
 *     <li>{@link #invokeDirect} is used for private instance methods and
 *         for constructors to call their superclass's constructor.</li>
 *     <li>{@link #invokeInterface} is used to invoke a method whose declaring
 *         type is an interface.</li>
 *     <li>{@link #invokeVirtual} is used to invoke any other method. The target
 *         must not be static, private, a constructor, or an interface
 *         method.</li>
 *     <li>{@link #invokeSuper} is used to invoke the closest superclass's
 *         virtual method. The target must not be static, private, a constructor
 *         method, or an interface method.</li>
 *     <li>{@link #newInstance} is used to invoke a constructor.</li>

 * </ul>
 * All invoke methods take a local for the return value. For void methods this
 * local is unused and may be null.
 *
 * <h3>Field Access</h3>
 * Read static fields using {@link #sget}; write them using {@link #sput}. For
 * instance values you'll need to specify the declaring instance; use {@link
 * #getThis} in an instance method to use {@code this}. Read instance values
 * using {@link #iget} and write them with {@link #iput}.
 *
 * <h3>Array Access</h3>
 * Allocate an array using {@link #newArray}. Read an array's length with {@link
 * #arrayLength} and its elements with {@link #aget}. Write an array's elements
 * with {@link #aput}.
 *
 * <h3>Types</h3>
 * Use {@link #cast} to perform either a <strong>numeric cast</strong> or a
 * <strong>type cast</strong>. Interrogate the type of a value in a local using
 * {@link #instanceOfType}.
 *
 * <h3>Synchronization</h3>
 * Acquire a monitor using {@link #monitorEnter}; release it with {@link
 * #monitorExit}. It is the caller's responsibility to guarantee that enter and
 * exit calls are balanced, even in the presence of exceptions thrown.
 *
 * <strong>Warning:</strong> Even if a method has the {@code synchronized} flag,
 * dex requires instructions to acquire and release monitors manually. A method
 * declared with {@link java.lang.reflect.Modifier#SYNCHRONIZED SYNCHRONIZED}
 * but without manual calls to {@code monitorEnter()} and {@code monitorExit()}
 * will not be synchronized when executed.
 */
public final class Code {
    private final MethodId<?, ?> method;
    /**
     * All allocated labels. Although the order of the labels in this list
     * shouldn't impact behavior, it is used to determine basic block indices.
     */
    private final List<Label> labels = new ArrayList<Label>();

    /**
     * The label currently receiving instructions. This is null if the most
     * recent instruction was a return or goto.
     */
    private Label currentLabel;

    /** true once we've fixed the positions of the parameter registers */
    private boolean localsInitialized;

    private final Local<?> thisLocal;

    /**
     * The parameters on this method. If this is non-static, the first parameter
     * is 'thisLocal' and we have to offset the user's indices by one.
     */
    private final List<Local<?>> parameters = new ArrayList<Local<?>>();
    private final List<Local<?>> locals = new ArrayList<Local<?>>();
    private SourcePosition sourcePosition = SourcePosition.NO_INFO;
    private final List<TypeId<?>> catchTypes = new ArrayList<TypeId<?>>();
    private final List<Label> catchLabels = new ArrayList<Label>();
    private StdTypeList catches = StdTypeList.EMPTY;

    Code(DexMaker.MethodDeclaration methodDeclaration) {
        this.method = methodDeclaration.method;
        if (methodDeclaration.isStatic()) {
            thisLocal = null;
        } else {
            thisLocal = Local.get(this, method.declaringType);
            parameters.add(thisLocal);
        }
        for (TypeId<?> parameter : method.parameters.types) {
            parameters.add(Local.get(this, parameter));
        }
        this.currentLabel = new Label();
        adopt(this.currentLabel);
        this.currentLabel.marked = true;
    }

    public <T> Local<T> newLocal(TypeId<T> type) {
        if (localsInitialized) {
            throw new IllegalStateException("Cannot allocate locals after adding instructions");
        }
        Local<T> result = Local.get(this, type);
        locals.add(result);
        return result;
    }

    public <T> Local<T> getParameter(int index, TypeId<T> type) {
        if (thisLocal != null) {
            index++; // adjust for the hidden 'this' parameter
        }
        return coerce(parameters.get(index), type);
    }

    public <T> Local<T> getThis(TypeId<T> type) {
        if (thisLocal == null) {
            throw new IllegalStateException("static methods cannot access 'this'");
        }
        return coerce(thisLocal, type);
    }

    @SuppressWarnings("unchecked") // guarded by an equals check
    private <T> Local<T> coerce(Local<?> local, TypeId<T> expectedType) {
        if (!local.type.equals(expectedType)) {
            throw new IllegalArgumentException(
                    "requested " + expectedType + " but was " + local.type);
        }
        return (Local<T>) local;
    }

    /**
     * Assigns registers to locals. From the spec:
     *  "the N arguments to a method land in the last N registers of the
     *   method's invocation frame, in order. Wide arguments consume two
     *   registers. Instance methods are passed a this reference as their
     *   first argument."
     *
     * In addition to assigning registers to each of the locals, this creates
     * instructions to move parameters into their initial registers. These
     * instructions are inserted before the code's first real instruction.
     */
    void initializeLocals() {
        if (localsInitialized) {
            throw new AssertionError();
        }
        localsInitialized = true;

        int reg = 0;
        for (Local<?> local : locals) {
            reg += local.initialize(reg);
        }
        int firstParamReg = reg;
        List<Insn> moveParameterInstructions = new ArrayList<Insn>();
        for (Local<?> local : parameters) {
            CstInteger paramConstant = CstInteger.make(reg - firstParamReg);
            reg += local.initialize(reg);
            moveParameterInstructions.add(new PlainCstInsn(Rops.opMoveParam(local.type.ropType),
                    sourcePosition, local.spec(), RegisterSpecList.EMPTY, paramConstant));
        }
        labels.get(0).instructions.addAll(0, moveParameterInstructions);
    }

    /**
     * Returns the number of registers to hold the parameters. This includes the
     * 'this' parameter if it exists.
     */
    int paramSize() {
        int result = 0;
        for (Local<?> local : parameters) {
            result += local.size();
        }
        return result;
    }

    // labels

    /**
     * Assigns {@code target} to this code.
     */
    private void adopt(Label target) {
        if (target.code == this) {
            return; // already adopted
        }
        if (target.code != null) {
            throw new IllegalArgumentException("Cannot adopt label; it belongs to another Code");
        }
        target.code = this;
        labels.add(target);
    }

    /**
     * Start defining instructions for the named label.
     */
    public void mark(Label label) {
        adopt(label);
        if (label.marked) {
            throw new IllegalStateException("already marked");
        }
        label.marked = true;
        if (currentLabel != null) {
            jump(label); // blocks must end with a branch, return or throw
        }
        currentLabel = label;
    }

    public void jump(Label target) {
        adopt(target);
        addInstruction(new PlainInsn(Rops.GOTO, sourcePosition, null, RegisterSpecList.EMPTY),
                target);
    }

    public void addCatchClause(TypeId<?> throwable, Label catchClause) {
        if (catchTypes.contains(throwable)) {
            throw new IllegalArgumentException("Already caught: " + throwable);
        }
        adopt(catchClause);
        catchTypes.add(throwable);
        catches = toTypeList(catchTypes);
        catchLabels.add(catchClause);
    }

    public Label removeCatchClause(TypeId<?> throwable) {
        int index = catchTypes.indexOf(throwable);
        if (index == -1) {
            throw new IllegalArgumentException("No catch clause: " + throwable);
        }
        catchTypes.remove(index);
        catches = toTypeList(catchTypes);
        return catchLabels.remove(index);
    }

    public void throwValue(Local<?> throwable) {
        addInstruction(new ThrowingInsn(Rops.THROW, sourcePosition,
                RegisterSpecList.make(throwable.spec()), catches));
    }

    private StdTypeList toTypeList(List<TypeId<?>> types) {
        StdTypeList result = new StdTypeList(types.size());
        for (int i = 0; i < types.size(); i++) {
            result.set(i, types.get(i).ropType);
        }
        return result;
    }

    private void addInstruction(Insn insn) {
        addInstruction(insn, null);
    }

    /**
     * @param branch the branches to follow; interpretation depends on the
     *     instruction's branchingness.
     */
    private void addInstruction(Insn insn, Label branch) {
        if (currentLabel == null || !currentLabel.marked) {
            throw new IllegalStateException("no current label");
        }
        currentLabel.instructions.add(insn);

        switch (insn.getOpcode().getBranchingness()) {
        case BRANCH_NONE:
            if (branch != null) {
                throw new IllegalArgumentException("unexpected branch: " + branch);
            }
            return;

        case BRANCH_RETURN:
            if (branch != null) {
                throw new IllegalArgumentException("unexpected branch: " + branch);
            }
            currentLabel = null;
            break;

        case BRANCH_GOTO:
            if (branch == null) {
                throw new IllegalArgumentException("branch == null");
            }
            currentLabel.primarySuccessor = branch;
            currentLabel = null;
            break;

        case Rop.BRANCH_IF:
            if (branch == null) {
                throw new IllegalArgumentException("branch == null");
            }
            splitCurrentLabel(branch, Collections.<Label>emptyList());
            break;

        case Rop.BRANCH_THROW:
            if (branch != null) {
                throw new IllegalArgumentException("unexpected branch: " + branch);
            }
            splitCurrentLabel(null, new ArrayList<Label>(catchLabels));
            break;

        default:
            throw new IllegalArgumentException();
        }
    }

    /**
     * Closes the current label and starts a new one.
     *
     * @param catchLabels an immutable list of catch labels
     */
    private void splitCurrentLabel(Label alternateSuccessor, List<Label> catchLabels) {
        Label newLabel = new Label();
        adopt(newLabel);
        currentLabel.primarySuccessor = newLabel;
        currentLabel.alternateSuccessor = alternateSuccessor;
        currentLabel.catchLabels = catchLabels;
        currentLabel = newLabel;
        currentLabel.marked = true;
    }

    // instructions: constants

    public <T> void loadConstant(Local<T> target, T value) {
        Rop rop = value == null
                ? Rops.CONST_OBJECT_NOTHROW
                : Rops.opConst(target.type.ropType);
        if (rop.getBranchingness() == BRANCH_NONE) {
            addInstruction(new PlainCstInsn(rop, sourcePosition, target.spec(),
                    RegisterSpecList.EMPTY, Constants.getConstant(value)));
        } else {
            addInstruction(new ThrowingCstInsn(rop, sourcePosition,
                    RegisterSpecList.EMPTY, catches, Constants.getConstant(value)));
            moveResult(target, true);
        }
    }

    // instructions: unary and binary

    public <T> void op(UnaryOp op, Local<T> target, Local<T> source) {
        addInstruction(new PlainInsn(op.rop(source.type), sourcePosition,
                target.spec(), source.spec()));
    }

    public <T> void op(BinaryOp op, Local<T> target, Local<T> a, Local<T> b) {
        Rop rop = op.rop(StdTypeList.make(a.type.ropType, b.type.ropType));
        RegisterSpecList sources = RegisterSpecList.make(a.spec(), b.spec());

        if (rop.getBranchingness() == BRANCH_NONE) {
            addInstruction(new PlainInsn(rop, sourcePosition, target.spec(), sources));
        } else {
            addInstruction(new ThrowingInsn(rop, sourcePosition, sources, catches));
            moveResult(target, true);
        }
    }

    // instructions: branches

    /**
     * Compare ints or references. If the comparison is true, execution jumps to
     * {@code trueLabel}. If it is false, execution continues to the next
     * instruction.
     */
    public <T> void compare(Comparison comparison, Label trueLabel, Local<T> a, Local<T> b) {
        adopt(trueLabel);
        // TODO: ops to compare with zero/null: just omit the 2nd local in StdTypeList.make()
        Rop rop = comparison.rop(StdTypeList.make(a.type.ropType, b.type.ropType));
        addInstruction(new PlainInsn(rop, sourcePosition, null,
                RegisterSpecList.make(a.spec(), b.spec())), trueLabel);
    }

    /**
     * Compare floats or doubles.
     */
    public <T extends Number> void compareFloatingPoint(
            Local<Integer> target, Local<T> a, Local<T> b, int nanValue) {
        Rop rop;
        if (nanValue == 1) {
            rop = Rops.opCmpg(a.type.ropType);
        } else if (nanValue == -1) {
            rop = Rops.opCmpl(a.type.ropType);
        } else {
            throw new IllegalArgumentException("expected 1 or -1 but was " + nanValue);
        }
        addInstruction(new PlainInsn(rop, sourcePosition, target.spec(),
                RegisterSpecList.make(a.spec(), b.spec())));
    }

    /**
     * Compare longs.
     */
    public void compareLongs(Local<Integer> target, Local<Long> a, Local<Long> b) {
        addInstruction(new PlainInsn(Rops.CMPL_LONG, sourcePosition, target.spec(),
                RegisterSpecList.make(a.spec(), b.spec())));
    }

    // instructions: fields

    public <D, V> void iget(FieldId<D, V> fieldId, Local<V> target, Local<D> instance) {
        addInstruction(new ThrowingCstInsn(Rops.opGetField(target.type.ropType), sourcePosition,
                RegisterSpecList.make(instance.spec()), catches, fieldId.constant));
        moveResult(target, true);
    }

    public <D, V> void iput(FieldId<D, V> fieldId, Local<D> instance, Local<V> source) {
        addInstruction(new ThrowingCstInsn(Rops.opPutField(source.type.ropType), sourcePosition,
                RegisterSpecList.make(source.spec(), instance.spec()), catches, fieldId.constant));
    }

    public <V> void sget(FieldId<?, V> fieldId, Local<V> target) {
        addInstruction(new ThrowingCstInsn(Rops.opGetStatic(target.type.ropType), sourcePosition,
                RegisterSpecList.EMPTY, catches, fieldId.constant));
        moveResult(target, true);
    }

    public <V> void sput(FieldId<?, V> fieldId, Local<V> source) {
        addInstruction(new ThrowingCstInsn(Rops.opPutStatic(source.type.ropType), sourcePosition,
                RegisterSpecList.make(source.spec()), catches, fieldId.constant));
    }

    // instructions: invoke

    public <T> void newInstance(Local<T> target, MethodId<T, Void> constructor, Local<?>... args) {
        if (target == null) {
            throw new IllegalArgumentException();
        }
        addInstruction(new ThrowingCstInsn(Rops.NEW_INSTANCE, sourcePosition,
                RegisterSpecList.EMPTY, catches, constructor.declaringType.constant));
        moveResult(target, true);
        invokeDirect(constructor, null, target, args);
    }

    public <R> void invokeStatic(MethodId<?, R> method, Local<? super R> target, Local<?>... args) {
        invoke(Rops.opInvokeStatic(method.prototype(true)), method, target, null, args);
    }

    public <D, R> void invokeVirtual(MethodId<D, R> method, Local<? super R> target,
            Local<? extends D> object, Local<?>... args) {
        invoke(Rops.opInvokeVirtual(method.prototype(true)), method, target, object, args);
    }

    public <D, R> void invokeDirect(MethodId<D, R> method, Local<? super R> target,
            Local<? extends D> object, Local<?>... args) {
        invoke(Rops.opInvokeDirect(method.prototype(true)), method, target, object, args);
    }

    public <D, R> void invokeSuper(MethodId<D, R> method, Local<? super R> target,
            Local<? extends D> object, Local<?>... args) {
        invoke(Rops.opInvokeSuper(method.prototype(true)), method, target, object, args);
    }

    public <D, R> void invokeInterface(MethodId<D, R> method, Local<? super R> target,
            Local<? extends D> object, Local<?>... args) {
        invoke(Rops.opInvokeInterface(method.prototype(true)), method, target, object, args);
    }

    private <D, R> void invoke(Rop rop, MethodId<D, R> method, Local<? super R> target,
            Local<? extends D> object, Local<?>... args) {
        addInstruction(new ThrowingCstInsn(rop, sourcePosition, concatenate(object, args),
                catches, method.constant));
        if (target != null) {
            moveResult(target, false);
        }
    }

    // instructions: types

    public void instanceOfType(Local<?> target, Local<?> source, TypeId<?> type) {
        addInstruction(new ThrowingCstInsn(Rops.INSTANCE_OF, sourcePosition,
                RegisterSpecList.make(source.spec()), catches, type.constant));
        moveResult(target, true);
    }

    /**
     * Performs either a numeric cast or a type cast.
     *
     * <h3>Numeric Casts</h3>
     * Converts a primitive to a different representation. Numeric casts may
     * be lossy. For example, converting the double {@code 1.8d} to an integer
     * yields {@code 1}, losing the fractional part. Converting the integer
     * {@code 0x12345678} to a short yields {@code 0x5678}, losing the high
     * bytes. The following numeric casts are supported:
     *
     * <p><table border="1">
     * <tr><th>From</th><th>To</th></tr>
     * <tr><td>int</td><td>byte, char, short, long, float, double</td></tr>
     * <tr><td>long</td><td>int, float, double</td></tr>
     * <tr><td>float</td><td>int, long, double</td></tr>
     * <tr><td>double</td><td>int, long, float</td></tr>
     * </table>
     *
     * <p>For some primitive conversions it will be necessary to chain multiple
     * cast operations. For example, to go from float to short one would first
     * cast float to int and then int to short.
     *
     * <p>Numeric casts never throw {@link ClassCastException}.
     *
     * <h3>Type Casts</h3>
     * Checks that a reference value is assignable to the target type. If it is
     * assignable it is copied to the target local. If it is not assignable a
     * {@link ClassCastException} is thrown.
     */
    public void cast(Local<?> target, Local<?> source) {
        if (source.getType().ropType.isReference()) {
            addInstruction(new ThrowingCstInsn(Rops.CHECK_CAST, sourcePosition,
                    RegisterSpecList.make(source.spec()), catches, target.type.constant));
            moveResult(target, true);
        } else {
            addInstruction(new PlainInsn(getCastRop(source.type.ropType, target.type.ropType),
                    sourcePosition, target.spec(), source.spec()));
        }
    }

    private Rop getCastRop(com.android.dx.rop.type.Type sourceType,
            com.android.dx.rop.type.Type targetType) {
        if (sourceType.getBasicType() == BT_INT) {
            switch (targetType.getBasicType()) {
            case BT_SHORT:
                return Rops.TO_SHORT;
            case BT_CHAR:
                return Rops.TO_CHAR;
            case BT_BYTE:
                return Rops.TO_BYTE;
            }
        }
        return Rops.opConv(targetType, sourceType);
    }

    // instructions: arrays

    public <T> void arrayLength(Local<Integer> target, Local<T> array) {
        addInstruction(new ThrowingInsn(Rops.ARRAY_LENGTH, sourcePosition,
                RegisterSpecList.make(array.spec()), catches));
        moveResult(target, true);
    }

    public <T> void newArray(Local<T> target, Local<Integer> length) {
        addInstruction(new ThrowingCstInsn(Rops.opNewArray(target.type.ropType), sourcePosition,
                RegisterSpecList.make(length.spec()), catches, target.type.constant));
        moveResult(target, true);
    }

    public void aget(Local<?> target, Local<?> array, Local<Integer> index) {
        addInstruction(new ThrowingInsn(Rops.opAget(target.type.ropType), sourcePosition,
                RegisterSpecList.make(array.spec(), index.spec()), catches));
        moveResult(target, true);
    }

    public void aput(Local<?> array, Local<Integer> index, Local<?> source) {
        addInstruction(new ThrowingInsn(Rops.opAput(source.type.ropType), sourcePosition,
                RegisterSpecList.make(source.spec(), array.spec(), index.spec()), catches));
    }

    // instructions: return

    public void returnVoid() {
        if (!method.returnType.equals(TypeId.VOID)) {
            throw new IllegalArgumentException("declared " + method.returnType
                    + " but returned void");
        }
        addInstruction(new PlainInsn(Rops.RETURN_VOID, sourcePosition, null,
                RegisterSpecList.EMPTY));
    }

    public void returnValue(Local<?> result) {
        if (!result.type.equals(method.returnType)) {
            // TODO: this is probably too strict.
            throw new IllegalArgumentException("declared " + method.returnType
                    + " but returned " + result.type);
        }
        addInstruction(new PlainInsn(Rops.opReturn(result.type.ropType), sourcePosition,
                null, RegisterSpecList.make(result.spec())));
    }

    private void moveResult(Local<?> target, boolean afterNonInvokeThrowingInsn) {
        Rop rop = afterNonInvokeThrowingInsn
                ? Rops.opMoveResultPseudo(target.type.ropType)
                : Rops.opMoveResult(target.type.ropType);
        addInstruction(new PlainInsn(rop, sourcePosition, target.spec(), RegisterSpecList.EMPTY));
    }

    // instructions; synchronized

    public void monitorEnter(Local<?> monitor) {
        addInstruction(new ThrowingInsn(Rops.MONITOR_ENTER, sourcePosition,
                RegisterSpecList.make(monitor.spec()), catches));
    }

    public void monitorExit(Local<?> monitor) {
        addInstruction(new ThrowingInsn(Rops.MONITOR_ENTER, sourcePosition,
                RegisterSpecList.make(monitor.spec()), catches));
    }

    // produce BasicBlocks for dex

    BasicBlockList toBasicBlocks() {
        if (!localsInitialized) {
            initializeLocals();
        }

        cleanUpLabels();

        BasicBlockList result = new BasicBlockList(labels.size());
        for (int i = 0; i < labels.size(); i++) {
            result.set(i, labels.get(i).toBasicBlock());
        }
        return result;
    }

    /**
     * Removes empty labels and assigns IDs to non-empty labels.
     */
    private void cleanUpLabels() {
        int id = 0;
        for (Iterator<Label> i = labels.iterator(); i.hasNext();) {
            Label label = i.next();
            if (label.isEmpty()) {
                i.remove();
            } else {
                label.compact();
                label.id = id++;
            }
        }
    }

    private static RegisterSpecList concatenate(Local<?> first, Local<?>[] rest) {
        int offset = (first != null) ? 1 : 0;
        RegisterSpecList result = new RegisterSpecList(offset + rest.length);
        if (first != null) {
            result.set(0, first.spec());
        }
        for (int i = 0; i < rest.length; i++) {
            result.set(i + offset, rest[i].spec());
        }
        return result;
    }
}