partialevaluator.java

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    /**
     * Returns the instruction offset at which this initializer is calling
     * the "super" or "this" initializer method, or <code>NONE</code> if it is
     * not an initializer.
     */
    public int superInitializationOffset()
    {
        return branchTargetFinder.superInitializationOffset();
    }


    /**
     * Returns the offset of the 'new' instruction that corresponds to the
     * invocation of the instance initializer at the given offset, or
     * <code>AT_METHOD_ENTRY</code> if the invocation is calling the "super" or
     * "this" initializer method, , or <code>NONE</code> if it is not a 'new'
     * instruction.
     */
    public int creationOffset(int offset)
    {
        return branchTargetFinder.creationOffset(offset);
    }


    /**
     * Returns the variables before execution of the instruction at the given
     * offset.
     */
    public TracedVariables getVariablesBefore(int instructionOffset)
    {
        return variablesBefore[instructionOffset];
    }


    /**
     * Returns the variables after execution of the instruction at the given
     * offset.
     */
    public TracedVariables getVariablesAfter(int instructionOffset)
    {
        return variablesAfter[instructionOffset];
    }


    /**
     * Returns the instruction offsets that set the variable that is being
     * used at the given instruction offset.
     */
    public InstructionOffsetValue varProducerOffsets(int instructionOffset)
    {
        return varProducerValues[instructionOffset];
    }


    /**
     * Returns the stack before execution of the instruction at the given
     * offset.
     */
    public TracedStack getStackBefore(int instructionOffset)
    {
        return stacksBefore[instructionOffset];
    }


    /**
     * Returns the stack after execution of the instruction at the given
     * offset.
     */
    public TracedStack getStackAfter(int instructionOffset)
    {
        return stacksAfter[instructionOffset];
    }


    /**
     * Returns the instruction offsets that set the stack entries that are being
     * used at the given instruction offset.
     */
    public InstructionOffsetValue stackProducerOffsets(int instructionOffset)
    {
        return stackProducerValues[instructionOffset];
    }


    /**
     * Returns the instruction offsets that branch to the given instruction
     * offset.
     */
    public InstructionOffsetValue branchOrigins(int instructionOffset)
    {
        return branchOriginValues[instructionOffset];
    }


    /**
     * Returns the instruction offsets to which the given instruction offset
     * branches.
     */
    public InstructionOffsetValue branchTargets(int instructionOffset)
    {
        return branchTargetValues[instructionOffset];
    }


    /**
     * Returns the variable that is initialized at the given instruction offset,
     * or <code>NONE</code> if no variable was initialized.
     */
    public int initializedVariable(int instructionOffset)
    {
        return initializedVariables[instructionOffset];
    }


    // Implementations for ExceptionInfoVisitor.

    public void visitExceptionInfo(Clazz clazz, Method method, CodeAttribute codeAttribute, ExceptionInfo exceptionInfo)
    {
        int startPC = exceptionInfo.u2startPC;
        int endPC   = exceptionInfo.u2endPC;

        // Do we have to evaluate this exception catch block?
        if (isTraced(startPC, endPC))
        {
            int handlerPC = exceptionInfo.u2handlerPC;

            if (DEBUG) System.out.println("Partial evaluation of exception ["+startPC +","+endPC +"] -> ["+handlerPC+"]:");

            // Reuse the existing variables and stack objects, ensuring the
            // right size.
            TracedVariables variables = new TracedVariables(codeAttribute.u2maxLocals);
            TracedStack     stack     = new TracedStack(codeAttribute.u2maxStack);

            // Initialize the trace values.
            Value storeValue = new InstructionOffsetValue(AT_CATCH_ENTRY);
            variables.setProducerValue(storeValue);
            stack.setProducerValue(storeValue);

            // Initialize the variables by generalizing the variables of the
            // try block. Make sure to include the results of the last
            // instruction for preverification.
            generalizeVariables(startPC,
                                endPC + (evaluateAllCode ? 1 : 0),
                                variables);

            // Initialize the the stack.
            //stack.push(valueFactory.createReference((ClassConstant)((ProgramClass)clazz).getConstant(exceptionInfo.u2catchType), false));
            String catchType = exceptionInfo.u2catchType != 0 ?
                 clazz.getClassName(exceptionInfo.u2catchType) :
                 ClassConstants.INTERNAL_NAME_JAVA_LANG_THROWABLE;

            // TODO: Get catch type class from class constant pool entry.
            stack.push(valueFactory.createReferenceValue(catchType,
                                                         null,
                                                         false));

            int evaluationCount = evaluationCounts[handlerPC];

            // Evaluate the instructions, starting at the entry point.
            evaluateInstructionBlock(clazz,
                                     method,
                                     codeAttribute,
                                     variables,
                                     stack,
                                     handlerPC);

            // Remember to evaluate all exception handlers once more.
            if (!evaluateExceptions)
            {
                evaluateExceptions = evaluationCount < evaluationCounts[handlerPC];
            }
        }
        else if (evaluateAllCode)
        {
            if (DEBUG) System.out.println("No information for partial evaluation of exception ["+startPC +","+endPC +"] -> ["+exceptionInfo.u2handlerPC+"] yet");

            // We don't have any information on the try block yet, but we do
            // have to evaluate the exception handler.
            // Remember to evaluate all exception handlers once more.
            evaluateExceptions = true;
        }
        else
        {
            if (DEBUG) System.out.println("No information for partial evaluation of exception ["+startPC +","+endPC +"] -> ["+exceptionInfo.u2handlerPC+"]");
        }
    }


    // Utility methods to evaluate instruction blocks.

    /**
     * Evaluates a block of instructions, starting at the given offset and ending
     * at a branch instruction, a return instruction, or a throw instruction.
     */
    private void evaluateInstructionBlock(Clazz            clazz,
                                          Method           method,
                                          CodeAttribute    codeAttribute,
                                          TracedVariables  variables,
                                          TracedStack      stack,
                                          int              startOffset)
    {
        byte[] code = codeAttribute.code;

        if (DEBUG)
        {
             System.out.println("Instruction block starting at ["+startOffset+"] in "+
                                ClassUtil.externalFullMethodDescription(clazz.getName(),
                                                                        0,
                                                                        method.getName(clazz),
                                                                        method.getDescriptor(clazz)));
             System.out.println("Init vars:  "+variables);
             System.out.println("Init stack: "+stack);
        }

        Processor processor = new Processor(variables, stack, valueFactory, branchUnit, invocationUnit);

        int instructionOffset = startOffset;

        int maxOffset = startOffset;

        // Evaluate the subsequent instructions.
        while (true)
        {
            if (maxOffset < instructionOffset)
            {
                maxOffset = instructionOffset;
            }

            // Maintain a generalized local variable frame and stack at this
            // instruction offset, before execution.
            int evaluationCount = evaluationCounts[instructionOffset];
            if (evaluationCount == 0)
            {
                // First time we're passing by this instruction.
                if (variablesBefore[instructionOffset] == null)
                {
                    // There's not even a context at this index yet.
                    variablesBefore[instructionOffset] = new TracedVariables(variables);
                    stacksBefore[instructionOffset]    = new TracedStack(stack);
                }
                else
                {
                    // Reuse the context objects at this index.
                    variablesBefore[instructionOffset].initialize(variables);
                    stacksBefore[instructionOffset].copy(stack);
                }

                // We'll execute in the generalized context, because it is
                // the same as the current context.
                generalizedContexts[instructionOffset] = true;
            }
            else
            {
                // Merge in the current context.
                boolean variablesChanged = variablesBefore[instructionOffset].generalize(variables, true);
                boolean stackChanged     = stacksBefore[instructionOffset].generalize(stack);

                // Bail out if the current context is the same as last time.
                if (!variablesChanged &&
                    !stackChanged     &&
                    generalizedContexts[instructionOffset])
                {
                    if (DEBUG) System.out.println("Repeated variables, stack, and branch targets");

                    break;
                }

                // See if this instruction has been evaluated an excessive number
                // of times.
                if (evaluationCount >= MAXIMUM_EVALUATION_COUNT)
                {
                    if (DEBUG) System.out.println("Generalizing current context after "+evaluationCount+" evaluations");

                    // Continue, but generalize the current context.
                    // Note that the most recent variable values have to remain
                    // last in the generalizations, for the sake of the ret
                    // instruction.
                    variables.generalize(variablesBefore[instructionOffset], false);
                    stack.generalize(stacksBefore[instructionOffset]);

                    // We'll execute in the generalized context.
                    generalizedContexts[instructionOffset] = true;
                }
                else
                {
                    // We'll execute in the current context.
                    generalizedContexts[instructionOffset] = false;
                }
            }

            // We'll evaluate this instruction.
            evaluationCounts[instructionOffset]++;

            // Remember this instruction's offset with any stored value.
            Value storeValue = new InstructionOffsetValue(instructionOffset);
            variables.setProducerValue(storeValue);
            stack.setProducerValue(storeValue);

            // Reset the trace value.
            InstructionOffsetValue traceValue = InstructionOffsetValue.EMPTY_VALUE;
            variables.setCollectedProducerValue(traceValue);
            stack.setCollectedProducerValue(traceValue);

            // Reset the initialization flag.
            variables.resetInitialization();

            // Note that the instruction is only volatile.
            Instruction instruction = InstructionFactory.create(code, instructionOffset);

            // By default, the next instruction will be the one after this
            // instruction.
            int nextInstructionOffset = instructionOffset +
                                        instruction.length(instructionOffset);
            InstructionOffsetValue nextInstructionOffsetValue = new InstructionOffsetValue(nextInstructionOffset);
            branchUnit.resetCalled();
            branchUnit.setTraceBranchTargets(nextInstructionOffsetValue);

            if (DEBUG)
            {
                System.out.println(instruction.toString(instructionOffset));
            }

            try
            {
                // Process the instruction. The processor may modify the
                // variables and the stack, and it may call the branch unit
                // and the invocation unit.
                instruction.accept(clazz,
                                   method,
                                   codeAttribute,