steppattern.java

java1.6众多例子参考

	    il.append(SWAP);
	    il.append(new INVOKEINTERFACE(getEType, 2));
	    il.append(new PUSH(cpg, _nodeType));
	
	    // Need to allow for long jumps here
	    final BranchHandle icmp = il.append(new IF_ICMPEQ(null));
	    _falseList.add(il.append(new GOTO_W(null)));
	    icmp.setTarget(il.append(NOP));
	}
    }

    private void translateNoContext(ClassGenerator classGen, 
				    MethodGenerator methodGen) {
	final ConstantPoolGen cpg = classGen.getConstantPool();
	final InstructionList il = methodGen.getInstructionList();

	// Push current node on the stack
	il.append(methodGen.loadCurrentNode());
	il.append(SWAP);

	// Overwrite current node with matching node
	il.append(methodGen.storeCurrentNode());

	// If pattern not reduced then check kernel
	if (!_isEpsilon) {
	    il.append(methodGen.loadCurrentNode());
	    translateKernel(classGen, methodGen);
	}

	// Compile the expressions within the predicates
	final int n = _predicates.size();
	for (int i = 0; i < n; i++) {
	    Predicate pred = (Predicate)_predicates.elementAt(i);
	    Expression exp = pred.getExpr();
	    exp.translateDesynthesized(classGen, methodGen);
	    _trueList.append(exp._trueList);
	    _falseList.append(exp._falseList);
	}

	// Backpatch true list and restore current iterator/node
	InstructionHandle restore;
	restore = il.append(methodGen.storeCurrentNode());
	backPatchTrueList(restore);
	BranchHandle skipFalse = il.append(new GOTO(null));

	// Backpatch false list and restore current iterator/node
	restore = il.append(methodGen.storeCurrentNode());
	backPatchFalseList(restore);
	_falseList.add(il.append(new GOTO(null)));

	// True list falls through
	skipFalse.setTarget(il.append(NOP));
    }

    private void translateSimpleContext(ClassGenerator classGen, 
					MethodGenerator methodGen) {
	int index;
	final ConstantPoolGen cpg = classGen.getConstantPool();
	final InstructionList il = methodGen.getInstructionList();

	// Store matching node into a local variable
	LocalVariableGen match;
	match = methodGen.addLocalVariable("step_pattern_tmp1", 
					   Util.getJCRefType(NODE_SIG),
					   il.getEnd(), null);
	il.append(new ISTORE(match.getIndex()));

	// If pattern not reduced then check kernel
	if (!_isEpsilon) {
	    il.append(new ILOAD(match.getIndex()));
 	    translateKernel(classGen, methodGen);
	}

	// Push current iterator and current node on the stack
	il.append(methodGen.loadCurrentNode());
	il.append(methodGen.loadIterator());

	// Create a new matching iterator using the matching node
	index = cpg.addMethodref(MATCHING_ITERATOR, "<init>", 
				 "(I" + NODE_ITERATOR_SIG + ")V");

        // Backwards branches are prohibited if an uninitialized object is
        // on the stack by section 4.9.4 of the JVM Specification, 2nd Ed.
        // We don't know whether this code might contain backwards branches,
        // so we mustn't create the new object until after we've created
        // the suspect arguments to its constructor.  Instead we calculate
        // the values of the arguments to the constructor first, store them
        // in temporary variables, create the object and reload the
        // arguments from the temporaries to avoid the problem.

	_step.translate(classGen, methodGen);
        LocalVariableGen stepIteratorTemp =
                methodGen.addLocalVariable("step_pattern_tmp2",
                                           Util.getJCRefType(NODE_ITERATOR_SIG),
                                           il.getEnd(), null);
        il.append(new ASTORE(stepIteratorTemp.getIndex()));

	il.append(new NEW(cpg.addClass(MATCHING_ITERATOR)));
	il.append(DUP);
	il.append(new ILOAD(match.getIndex()));
        il.append(new ALOAD(stepIteratorTemp.getIndex()));
	il.append(new INVOKESPECIAL(index));

	// Get the parent of the matching node
	il.append(methodGen.loadDOM());
	il.append(new ILOAD(match.getIndex()));
	index = cpg.addInterfaceMethodref(DOM_INTF, GET_PARENT, GET_PARENT_SIG);
	il.append(new INVOKEINTERFACE(index, 2));

	// Start the iterator with the parent 
	il.append(methodGen.setStartNode());

	// Overwrite current iterator and current node
	il.append(methodGen.storeIterator());
	il.append(new ILOAD(match.getIndex()));
	il.append(methodGen.storeCurrentNode());

	// Translate the expression of the predicate 
	Predicate pred = (Predicate) _predicates.elementAt(0);
	Expression exp = pred.getExpr();
	exp.translateDesynthesized(classGen, methodGen);

	// Backpatch true list and restore current iterator/node
	InstructionHandle restore = il.append(methodGen.storeIterator());
	il.append(methodGen.storeCurrentNode());
	exp.backPatchTrueList(restore);
	BranchHandle skipFalse = il.append(new GOTO(null));

	// Backpatch false list and restore current iterator/node
	restore = il.append(methodGen.storeIterator());
	il.append(methodGen.storeCurrentNode());
	exp.backPatchFalseList(restore);
	_falseList.add(il.append(new GOTO(null)));

	// True list falls through
	skipFalse.setTarget(il.append(NOP));
    }

    private void translateGeneralContext(ClassGenerator classGen, 
					 MethodGenerator methodGen) {
	final ConstantPoolGen cpg = classGen.getConstantPool();
	final InstructionList il = methodGen.getInstructionList();

	int iteratorIndex = 0;
	BranchHandle ifBlock = null;
	LocalVariableGen iter, node, node2;
	final String iteratorName = getNextFieldName();

	// Store node on the stack into a local variable
	node = methodGen.addLocalVariable("step_pattern_tmp1", 
					  Util.getJCRefType(NODE_SIG),
					  il.getEnd(), null);
	il.append(new ISTORE(node.getIndex()));

	// Create a new local to store the iterator
	iter = methodGen.addLocalVariable("step_pattern_tmp2", 
					  Util.getJCRefType(NODE_ITERATOR_SIG),
					  il.getEnd(), null);

	// Add a new private field if this is the main class
	if (!classGen.isExternal()) {
	    final Field iterator =
		new Field(ACC_PRIVATE, 
			  cpg.addUtf8(iteratorName),
			  cpg.addUtf8(NODE_ITERATOR_SIG),
			  null, cpg.getConstantPool());
	    classGen.addField(iterator);
	    iteratorIndex = cpg.addFieldref(classGen.getClassName(), 
					    iteratorName,
					    NODE_ITERATOR_SIG);

	    il.append(classGen.loadTranslet());
	    il.append(new GETFIELD(iteratorIndex));
	    il.append(DUP);
	    il.append(new ASTORE(iter.getIndex()));
	    ifBlock = il.append(new IFNONNULL(null));
	    il.append(classGen.loadTranslet());
	}	

	// Compile the step created at type checking time
	_step.translate(classGen, methodGen);
	il.append(new ASTORE(iter.getIndex()));

	// If in the main class update the field too
	if (!classGen.isExternal()) {
	    il.append(new ALOAD(iter.getIndex()));
	    il.append(new PUTFIELD(iteratorIndex));
	    ifBlock.setTarget(il.append(NOP));
	}

	// Get the parent of the node on the stack
	il.append(methodGen.loadDOM());
	il.append(new ILOAD(node.getIndex()));
	int index = cpg.addInterfaceMethodref(DOM_INTF,
					      GET_PARENT, GET_PARENT_SIG);
	il.append(new INVOKEINTERFACE(index, 2));

	// Initialize the iterator with the parent
	il.append(new ALOAD(iter.getIndex()));
	il.append(SWAP);
	il.append(methodGen.setStartNode());

	/* 
	 * Inline loop:
	 *
	 * int node2;
	 * while ((node2 = iter.next()) != NodeIterator.END 
	 *		  && node2 < node);
	 * return node2 == node; 
	 */
	BranchHandle skipNext;
	InstructionHandle begin, next;
	node2 = methodGen.addLocalVariable("step_pattern_tmp3", 
					   Util.getJCRefType(NODE_SIG),
					   il.getEnd(), null);

	skipNext = il.append(new GOTO(null));
	next = il.append(new ALOAD(iter.getIndex()));
	begin = il.append(methodGen.nextNode());
	il.append(DUP);
	il.append(new ISTORE(node2.getIndex()));
	_falseList.add(il.append(new IFLT(null)));	// NodeIterator.END

	il.append(new ILOAD(node2.getIndex()));
	il.append(new ILOAD(node.getIndex()));
	il.append(new IF_ICMPLT(next));

	il.append(new ILOAD(node2.getIndex()));
	il.append(new ILOAD(node.getIndex()));
	_falseList.add(il.append(new IF_ICMPNE(null)));

	skipNext.setTarget(begin);
    }
	
    public void translate(ClassGenerator classGen, MethodGenerator methodGen) {
	final ConstantPoolGen cpg = classGen.getConstantPool();
	final InstructionList il = methodGen.getInstructionList();

	if (hasPredicates()) {
	    switch (_contextCase) {
	    case NO_CONTEXT:
		translateNoContext(classGen, methodGen);
		break;
		
	    case SIMPLE_CONTEXT:
		translateSimpleContext(classGen, methodGen);
		break;
		
	    default:
		translateGeneralContext(classGen, methodGen);
		break;
	    }
	}
	else if (isWildcard()) {
	    il.append(POP); 	// true list falls through
	}
	else {
	    translateKernel(classGen, methodGen);
	}
    }
}