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	/*
	* Copyright (c) 2014, Oracle and/or its affiliates. All rights reserved.
	* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
	*
	* This code is free software; you can redistribute it and/or modify it
	* under the terms of the GNU General Public License version 2 only, as
	* published by the Free Software Foundation. Oracle designates this
	* particular file as subject to the "Classpath" exception as provided
	* by Oracle in the LICENSE file that accompanied this code.
	*
	* This code is distributed in the hope that it will be useful, but WITHOUT
	* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
	* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
	* version 2 for more details (a copy is included in the LICENSE file that
	* accompanied this code).
	*
	* You should have received a copy of the GNU General Public License version
	* 2 along with this work; if not, write to the Free Software Foundation,
	* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
	*
	* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
	* or visit www.oracle.com if you need additional information or have any
	* questions.
	*/

	package java.lang.invoke;

	import java.lang.ref.SoftReference;
	import java.util.Arrays;
	import static java.lang.invoke.LambdaForm.*;
	import static java.lang.invoke.LambdaForm.BasicType.*;
	import static java.lang.invoke.MethodHandleImpl.Intrinsic;
	import java.util.Collections;
	import java.util.concurrent.ConcurrentHashMap;

	import sun.invoke.util.Wrapper;

	/** Transforms on LFs.
	* A lambda-form editor can derive new LFs from its base LF.
	* The editor can cache derived LFs, which simplifies the reuse of their underlying bytecodes.
	* To support this caching, a LF has an optional pointer to its editor.
	*/
	class LambdaFormEditor {
	final LambdaForm lambdaForm;

	private LambdaFormEditor(LambdaForm lambdaForm) {
	this.lambdaForm = lambdaForm;
	}

	// Factory method.
	static LambdaFormEditor lambdaFormEditor(LambdaForm lambdaForm) {
	// TO DO: Consider placing intern logic here, to cut down on duplication.
	// lambdaForm = findPreexistingEquivalent(lambdaForm)

	// Always use uncustomized version for editing.
	// It helps caching and customized LambdaForms reuse transformCache field to keep a link to uncustomized version.
	return new LambdaFormEditor(lambdaForm.uncustomize());
	}

	/** A description of a cached transform, possibly associated with the result of the transform.
	* The logical content is a sequence of byte values, starting with a Kind.ordinal value.
	* The sequence is unterminated, ending with an indefinite number of zero bytes.
	* Sequences that are simple (short enough and with small enough values) pack into a 64-bit long.
	*/
	private static final class Transform extends SoftReference<LambdaForm> {
	final long packedBytes;
	final byte[] fullBytes;

	private enum Kind {
	NO_KIND, // necessary because ordinal must be greater than zero
	BIND_ARG, ADD_ARG, DUP_ARG,
	SPREAD_ARGS,
	FILTER_ARG, FILTER_RETURN, FILTER_RETURN_TO_ZERO,
	COLLECT_ARGS, COLLECT_ARGS_TO_VOID, COLLECT_ARGS_TO_ARRAY,
	FOLD_ARGS, FOLD_ARGS_TO_VOID,
	PERMUTE_ARGS
	//maybe add more for guard with test, catch exception, pointwise type conversions
	}

	private static final boolean STRESS_TEST = false; // turn on to disable most packing
	private static final int
	PACKED_BYTE_SIZE = (STRESS_TEST ? 2 : 4),
	PACKED_BYTE_MASK = (1 << PACKED_BYTE_SIZE) - 1,
	PACKED_BYTE_MAX_LENGTH = (STRESS_TEST ? 3 : 64 / PACKED_BYTE_SIZE);

	private static long packedBytes(byte[] bytes) {
	if (bytes.length > PACKED_BYTE_MAX_LENGTH) return 0;
	long pb = 0;
	int bitset = 0;
	for (int i = 0; i < bytes.length; i++) {
	int b = bytes[i] & 0xFF;
	bitset \|= b;
	pb \|= (long)b << (i * PACKED_BYTE_SIZE);
	}
	if (!inRange(bitset))
	return 0;
	return pb;
	}
	private static long packedBytes(int b0, int b1) {
	assert(inRange(b0 \| b1));
	return ( (b0 << 0*PACKED_BYTE_SIZE)
	\| (b1 << 1*PACKED_BYTE_SIZE));
	}
	private static long packedBytes(int b0, int b1, int b2) {
	assert(inRange(b0 \| b1 \| b2));
	return ( (b0 << 0*PACKED_BYTE_SIZE)
	\| (b1 << 1*PACKED_BYTE_SIZE)
	\| (b2 << 2*PACKED_BYTE_SIZE));
	}
	private static long packedBytes(int b0, int b1, int b2, int b3) {
	assert(inRange(b0 \| b1 \| b2 \| b3));
	return ( (b0 << 0*PACKED_BYTE_SIZE)
	\| (b1 << 1*PACKED_BYTE_SIZE)
	\| (b2 << 2*PACKED_BYTE_SIZE)
	\| (b3 << 3*PACKED_BYTE_SIZE));
	}
	private static boolean inRange(int bitset) {
	assert((bitset & 0xFF) == bitset); // incoming values must fit in unsigned byte
	return ((bitset & ~PACKED_BYTE_MASK) == 0);
	}
	private static byte[] fullBytes(int... byteValues) {
	byte[] bytes = new byte[byteValues.length];
	int i = 0;
	for (int bv : byteValues) {
	bytes[i++] = bval(bv);
	}
	assert(packedBytes(bytes) == 0);
	return bytes;
	}

	private byte byteAt(int i) {
	long pb = packedBytes;
	if (pb == 0) {
	if (i >= fullBytes.length) return 0;
	return fullBytes[i];
	}
	assert(fullBytes == null);
	if (i > PACKED_BYTE_MAX_LENGTH) return 0;
	int pos = (i * PACKED_BYTE_SIZE);
	return (byte)((pb >>> pos) & PACKED_BYTE_MASK);
	}

	Kind kind() { return Kind.values()[byteAt(0)]; }

	private Transform(long packedBytes, byte[] fullBytes, LambdaForm result) {
	super(result);
	this.packedBytes = packedBytes;
	this.fullBytes = fullBytes;
	}
	private Transform(long packedBytes) {
	this(packedBytes, null, null);
	assert(packedBytes != 0);
	}
	private Transform(byte[] fullBytes) {
	this(0, fullBytes, null);
	}

	private static byte bval(int b) {
	assert((b & 0xFF) == b); // incoming value must fit in unsigned byte
	return (byte)b;
	}
	private static byte bval(Kind k) {
	return bval(k.ordinal());
	}
	static Transform of(Kind k, int b1) {
	byte b0 = bval(k);
	if (inRange(b0 \| b1))
	return new Transform(packedBytes(b0, b1));
	else
	return new Transform(fullBytes(b0, b1));
	}
	static Transform of(Kind k, int b1, int b2) {
	byte b0 = (byte) k.ordinal();
	if (inRange(b0 \| b1 \| b2))
	return new Transform(packedBytes(b0, b1, b2));
	else
	return new Transform(fullBytes(b0, b1, b2));
	}
	static Transform of(Kind k, int b1, int b2, int b3) {
	byte b0 = (byte) k.ordinal();
	if (inRange(b0 \| b1 \| b2 \| b3))
	return new Transform(packedBytes(b0, b1, b2, b3));
	else
	return new Transform(fullBytes(b0, b1, b2, b3));
	}
	private static final byte[] NO_BYTES = {};
	static Transform of(Kind k, int... b123) {
	return ofBothArrays(k, b123, NO_BYTES);
	}
	static Transform of(Kind k, int b1, byte[] b234) {
	return ofBothArrays(k, new int[]{ b1 }, b234);
	}
	static Transform of(Kind k, int b1, int b2, byte[] b345) {
	return ofBothArrays(k, new int[]{ b1, b2 }, b345);
	}
	private static Transform ofBothArrays(Kind k, int[] b123, byte[] b456) {
	byte[] fullBytes = new byte[1 + b123.length + b456.length];
	int i = 0;
	fullBytes[i++] = bval(k);
	for (int bv : b123) {
	fullBytes[i++] = bval(bv);
	}
	for (byte bv : b456) {
	fullBytes[i++] = bv;
	}
	long packedBytes = packedBytes(fullBytes);
	if (packedBytes != 0)
	return new Transform(packedBytes);
	else
	return new Transform(fullBytes);
	}

	Transform withResult(LambdaForm result) {
	return new Transform(this.packedBytes, this.fullBytes, result);
	}

	@Override
	public boolean equals(Object obj) {
	return obj instanceof Transform && equals((Transform)obj);
	}
	public boolean equals(Transform that) {
	return this.packedBytes == that.packedBytes && Arrays.equals(this.fullBytes, that.fullBytes);
	}
	@Override
	public int hashCode() {
	if (packedBytes != 0) {
	assert(fullBytes == null);
	return Long.hashCode(packedBytes);
	}
	return Arrays.hashCode(fullBytes);
	}
	@Override
	public String toString() {
	StringBuilder buf = new StringBuilder();
	long bits = packedBytes;
	if (bits != 0) {
	buf.append("(");
	while (bits != 0) {
	buf.append(bits & PACKED_BYTE_MASK);
	bits >>>= PACKED_BYTE_SIZE;
	if (bits != 0) buf.append(",");
	}
	buf.append(")");
	}
	if (fullBytes != null) {
	buf.append("unpacked");
	buf.append(Arrays.toString(fullBytes));
	}
	LambdaForm result = get();
	if (result != null) {
	buf.append(" result=");
	buf.append(result);
	}
	return buf.toString();
	}
	}

	/** Find a previously cached transform equivalent to the given one, and return its result. */
	private LambdaForm getInCache(Transform key) {
	assert(key.get() == null);
	// The transformCache is one of null, Transform, Transform[], or ConcurrentHashMap.
	Object c = lambdaForm.transformCache;
	Transform k = null;
	if (c instanceof ConcurrentHashMap) {
	@SuppressWarnings("unchecked")
	ConcurrentHashMap<Transform,Transform> m = (ConcurrentHashMap<Transform,Transform>) c;
	k = m.get(key);
	} else if (c == null) {
	return null;
	} else if (c instanceof Transform) {
	// one-element cache avoids overhead of an array
	Transform t = (Transform)c;
	if (t.equals(key)) k = t;
	} else {
	Transform[] ta = (Transform[])c;
	for (int i = 0; i < ta.length; i++) {
	Transform t = ta[i];
	if (t == null) break;
	if (t.equals(key)) { k = t; break; }
	}
	}
	assert(k == null \|\| key.equals(k));
	return (k != null) ? k.get() : null;
	}

	/** Arbitrary but reasonable limits on Transform[] size for cache. */
	private static final int MIN_CACHE_ARRAY_SIZE = 4, MAX_CACHE_ARRAY_SIZE = 16;

	/** Cache a transform with its result, and return that result.
	* But if an equivalent transform has already been cached, return its result instead.
	*/
	private LambdaForm putInCache(Transform key, LambdaForm form) {
	key = key.withResult(form);
	for (int pass = 0; ; pass++) {
	Object c = lambdaForm.transformCache;
	if (c instanceof ConcurrentHashMap) {
	@SuppressWarnings("unchecked")
	ConcurrentHashMap<Transform,Transform> m = (ConcurrentHashMap<Transform,Transform>) c;
	Transform k = m.putIfAbsent(key, key);
	if (k == null) return form;
	LambdaForm result = k.get();
	if (result != null) {
	return result;
	} else {
	if (m.replace(key, k, key)) {
	return form;
	} else {
	continue;
	}
	}
	}
	assert(pass == 0);
	synchronized (lambdaForm) {
	c = lambdaForm.transformCache;
	if (c instanceof ConcurrentHashMap)
	continue;
	if (c == null) {
	lambdaForm.transformCache = key;
	return form;
	}
	Transform[] ta;
	if (c instanceof Transform) {
	Transform k = (Transform)c;
	if (k.equals(key)) {
	LambdaForm result = k.get();
	if (result == null) {
	lambdaForm.transformCache = key;
	return form;
	} else {
	return result;
	}
	} else if (k.get() == null) { // overwrite stale entry
	lambdaForm.transformCache = key;
	return form;
	}
	// expand one-element cache to small array
	ta = new Transform[MIN_CACHE_ARRAY_SIZE];
	ta[0] = k;
	lambdaForm.transformCache = ta;
	} else {
	// it is already expanded
	ta = (Transform[])c;
	}
	int len = ta.length;
	int stale = -1;
	int i;
	for (i = 0; i < len; i++) {
	Transform k = ta[i];
	if (k == null) {
	break;
	}
	if (k.equals(key)) {
	LambdaForm result = k.get();
	if (result == null) {
	ta[i] = key;
	return form;
	} else {
	return result;
	}
	} else if (stale < 0 && k.get() == null) {
	stale = i; // remember 1st stale entry index
	}
	}
	if (i < len \|\| stale >= 0) {
	// just fall through to cache update
	} else if (len < MAX_CACHE_ARRAY_SIZE) {
	len = Math.min(len * 2, MAX_CACHE_ARRAY_SIZE);
	ta = Arrays.copyOf(ta, len);
	lambdaForm.transformCache = ta;
	} else {
	ConcurrentHashMap<Transform, Transform> m = new ConcurrentHashMap<>(MAX_CACHE_ARRAY_SIZE * 2);
	for (Transform k : ta) {
	m.put(k, k);
	}
	lambdaForm.transformCache = m;
	// The second iteration will update for this query, concurrently.
	continue;
	}
	int idx = (stale >= 0) ? stale : i;
	ta[idx] = key;
	return form;
	}
	}
	}

	private LambdaFormBuffer buffer() {
	return new LambdaFormBuffer(lambdaForm);
	}

	/// Editing methods for method handles. These need to have fast paths.

	private BoundMethodHandle.SpeciesData oldSpeciesData() {
	return BoundMethodHandle.speciesData(lambdaForm);
	}
	private BoundMethodHandle.SpeciesData newSpeciesData(BasicType type) {
	return oldSpeciesData().extendWith(type);
	}

	BoundMethodHandle bindArgumentL(BoundMethodHandle mh, int pos, Object value) {
	assert(mh.speciesData() == oldSpeciesData());
	BasicType bt = L_TYPE;
	MethodType type2 = bindArgumentType(mh, pos, bt);
	LambdaForm form2 = bindArgumentForm(1+pos);
	return mh.copyWithExtendL(type2, form2, value);
	}
	BoundMethodHandle bindArgumentI(BoundMethodHandle mh, int pos, int value) {
	assert(mh.speciesData() == oldSpeciesData());
	BasicType bt = I_TYPE;
	MethodType type2 = bindArgumentType(mh, pos, bt);
	LambdaForm form2 = bindArgumentForm(1+pos);
	return mh.copyWithExtendI(type2, form2, value);
	}

	BoundMethodHandle bindArgumentJ(BoundMethodHandle mh, int pos, long value) {
	assert(mh.speciesData() == oldSpeciesData());
	BasicType bt = J_TYPE;
	MethodType type2 = bindArgumentType(mh, pos, bt);
	LambdaForm form2 = bindArgumentForm(1+pos);
	return mh.copyWithExtendJ(type2, form2, value);
	}

	BoundMethodHandle bindArgumentF(BoundMethodHandle mh, int pos, float value) {
	assert(mh.speciesData() == oldSpeciesData());
	BasicType bt = F_TYPE;
	MethodType type2 = bindArgumentType(mh, pos, bt);
	LambdaForm form2 = bindArgumentForm(1+pos);
	return mh.copyWithExtendF(type2, form2, value);
	}

	BoundMethodHandle bindArgumentD(BoundMethodHandle mh, int pos, double value) {
	assert(mh.speciesData() == oldSpeciesData());
	BasicType bt = D_TYPE;
	MethodType type2 = bindArgumentType(mh, pos, bt);
	LambdaForm form2 = bindArgumentForm(1+pos);
	return mh.copyWithExtendD(type2, form2, value);
	}

	private MethodType bindArgumentType(BoundMethodHandle mh, int pos, BasicType bt) {
	assert(mh.form.uncustomize() == lambdaForm);
	assert(mh.form.names[1+pos].type == bt);
	assert(BasicType.basicType(mh.type().parameterType(pos)) == bt);
	return mh.type().dropParameterTypes(pos, pos+1);
	}

	/// Editing methods for lambda forms.
	// Each editing method can (potentially) cache the edited LF so that it can be reused later.

	LambdaForm bindArgumentForm(int pos) {
	Transform key = Transform.of(Transform.Kind.BIND_ARG, pos);
	LambdaForm form = getInCache(key);
	if (form != null) {
	assert(form.parameterConstraint(0) == newSpeciesData(lambdaForm.parameterType(pos)));
	return form;
	}
	LambdaFormBuffer buf = buffer();
	buf.startEdit();

	BoundMethodHandle.SpeciesData oldData = oldSpeciesData();
	BoundMethodHandle.SpeciesData newData = newSpeciesData(lambdaForm.parameterType(pos));
	Name oldBaseAddress = lambdaForm.parameter(0); // BMH holding the values
	Name newBaseAddress;
	NamedFunction getter = newData.getterFunction(oldData.fieldCount());

	if (pos != 0) {
	// The newly created LF will run with a different BMH.
	// Switch over any pre-existing BMH field references to the new BMH class.
	buf.replaceFunctions(oldData.getterFunctions(), newData.getterFunctions(), oldBaseAddress);
	newBaseAddress = oldBaseAddress.withConstraint(newData);
	buf.renameParameter(0, newBaseAddress);
	buf.replaceParameterByNewExpression(pos, new Name(getter, newBaseAddress));
	} else {
	// cannot bind the MH arg itself, unless oldData is empty
	assert(oldData == BoundMethodHandle.SpeciesData.EMPTY);
	newBaseAddress = new Name(L_TYPE).withConstraint(newData);
	buf.replaceParameterByNewExpression(0, new Name(getter, newBaseAddress));
	buf.insertParameter(0, newBaseAddress);
	}

	form = buf.endEdit();
	return putInCache(key, form);
	}

	LambdaForm addArgumentForm(int pos, BasicType type) {
	Transform key = Transform.of(Transform.Kind.ADD_ARG, pos, type.ordinal());
	LambdaForm form = getInCache(key);
	if (form != null) {
	assert(form.arity == lambdaForm.arity+1);
	assert(form.parameterType(pos) == type);
	return form;
	}
	LambdaFormBuffer buf = buffer();
	buf.startEdit();

	buf.insertParameter(pos, new Name(type));

	form = buf.endEdit();
	return putInCache(key, form);
	}

	LambdaForm dupArgumentForm(int srcPos, int dstPos) {
	Transform key = Transform.of(Transform.Kind.DUP_ARG, srcPos, dstPos);
	LambdaForm form = getInCache(key);
	if (form != null) {
	assert(form.arity == lambdaForm.arity-1);
	return form;
	}
	LambdaFormBuffer buf = buffer();
	buf.startEdit();

	assert(lambdaForm.parameter(srcPos).constraint == null);
	assert(lambdaForm.parameter(dstPos).constraint == null);
	buf.replaceParameterByCopy(dstPos, srcPos);

	form = buf.endEdit();
	return putInCache(key, form);
	}

	LambdaForm spreadArgumentsForm(int pos, Class<?> arrayType, int arrayLength) {
	Class<?> elementType = arrayType.getComponentType();
	Class<?> erasedArrayType = arrayType;
	if (!elementType.isPrimitive())
	erasedArrayType = Object[].class;
	BasicType bt = basicType(elementType);
	int elementTypeKey = bt.ordinal();
	if (bt.basicTypeClass() != elementType) {
	if (elementType.isPrimitive()) {
	elementTypeKey = TYPE_LIMIT + Wrapper.forPrimitiveType(elementType).ordinal();
	}
	}
	Transform key = Transform.of(Transform.Kind.SPREAD_ARGS, pos, elementTypeKey, arrayLength);
	LambdaForm form = getInCache(key);
	if (form != null) {
	assert(form.arity == lambdaForm.arity - arrayLength + 1);
	return form;
	}
	LambdaFormBuffer buf = buffer();
	buf.startEdit();

	assert(pos <= MethodType.MAX_JVM_ARITY);
	assert(pos + arrayLength <= lambdaForm.arity);
	assert(pos > 0); // cannot spread the MH arg itself

	Name spreadParam = new Name(L_TYPE);
	Name checkSpread = new Name(MethodHandleImpl.Lazy.NF_checkSpreadArgument, spreadParam, arrayLength);

	// insert the new expressions
	int exprPos = lambdaForm.arity();
	buf.insertExpression(exprPos++, checkSpread);
	// adjust the arguments
	MethodHandle aload = MethodHandles.arrayElementGetter(erasedArrayType);
	for (int i = 0; i < arrayLength; i++) {
	Name loadArgument = new Name(aload, spreadParam, i);
	buf.insertExpression(exprPos + i, loadArgument);
	buf.replaceParameterByCopy(pos + i, exprPos + i);
	}
	buf.insertParameter(pos, spreadParam);

	form = buf.endEdit();
	return putInCache(key, form);
	}

	LambdaForm collectArgumentsForm(int pos, MethodType collectorType) {
	int collectorArity = collectorType.parameterCount();
	boolean dropResult = (collectorType.returnType() == void.class);
	if (collectorArity == 1 && !dropResult) {
	return filterArgumentForm(pos, basicType(collectorType.parameterType(0)));
	}
	BasicType[] newTypes = BasicType.basicTypes(collectorType.parameterList());
	Transform.Kind kind = (dropResult
	? Transform.Kind.COLLECT_ARGS_TO_VOID
	: Transform.Kind.COLLECT_ARGS);
	if (dropResult && collectorArity == 0) pos = 1; // pure side effect
	Transform key = Transform.of(kind, pos, collectorArity, BasicType.basicTypesOrd(newTypes));
	LambdaForm form = getInCache(key);
	if (form != null) {
	assert(form.arity == lambdaForm.arity - (dropResult ? 0 : 1) + collectorArity);
	return form;
	}
	form = makeArgumentCombinationForm(pos, collectorType, false, dropResult);
	return putInCache(key, form);
	}

	LambdaForm collectArgumentArrayForm(int pos, MethodHandle arrayCollector) {
	MethodType collectorType = arrayCollector.type();
	int collectorArity = collectorType.parameterCount();
	assert(arrayCollector.intrinsicName() == Intrinsic.NEW_ARRAY);
	Class<?> arrayType = collectorType.returnType();
	Class<?> elementType = arrayType.getComponentType();
	BasicType argType = basicType(elementType);
	int argTypeKey = argType.ordinal();
	if (argType.basicTypeClass() != elementType) {
	// return null if it requires more metadata (like String[].class)
	if (!elementType.isPrimitive())
	return null;
	argTypeKey = TYPE_LIMIT + Wrapper.forPrimitiveType(elementType).ordinal();
	}
	assert(collectorType.parameterList().equals(Collections.nCopies(collectorArity, elementType)));
	Transform.Kind kind = Transform.Kind.COLLECT_ARGS_TO_ARRAY;
	Transform key = Transform.of(kind, pos, collectorArity, argTypeKey);
	LambdaForm form = getInCache(key);
	if (form != null) {
	assert(form.arity == lambdaForm.arity - 1 + collectorArity);
	return form;
	}
	LambdaFormBuffer buf = buffer();
	buf.startEdit();

	assert(pos + 1 <= lambdaForm.arity);
	assert(pos > 0); // cannot filter the MH arg itself

	Name[] newParams = new Name[collectorArity];
	for (int i = 0; i < collectorArity; i++) {
	newParams[i] = new Name(pos + i, argType);
	}
	Name callCombiner = new Name(arrayCollector, (Object[]) /.../ newParams);

	// insert the new expression
	int exprPos = lambdaForm.arity();
	buf.insertExpression(exprPos, callCombiner);

	// insert new arguments
	int argPos = pos + 1; // skip result parameter
	for (Name newParam : newParams) {
	buf.insertParameter(argPos++, newParam);
	}
	assert(buf.lastIndexOf(callCombiner) == exprPos+newParams.length);
	buf.replaceParameterByCopy(pos, exprPos+newParams.length);

	form = buf.endEdit();
	return putInCache(key, form);
	}

	LambdaForm filterArgumentForm(int pos, BasicType newType) {
	Transform key = Transform.of(Transform.Kind.FILTER_ARG, pos, newType.ordinal());
	LambdaForm form = getInCache(key);
	if (form != null) {
	assert(form.arity == lambdaForm.arity);
	assert(form.parameterType(pos) == newType);
	return form;
	}

	BasicType oldType = lambdaForm.parameterType(pos);
	MethodType filterType = MethodType.methodType(oldType.basicTypeClass(),
	newType.basicTypeClass());
	form = makeArgumentCombinationForm(pos, filterType, false, false);
	return putInCache(key, form);
	}

	private LambdaForm makeArgumentCombinationForm(int pos,
	MethodType combinerType,
	boolean keepArguments, boolean dropResult) {
	LambdaFormBuffer buf = buffer();
	buf.startEdit();
	int combinerArity = combinerType.parameterCount();
	int resultArity = (dropResult ? 0 : 1);

	assert(pos <= MethodType.MAX_JVM_ARITY);
	assert(pos + resultArity + (keepArguments ? combinerArity : 0) <= lambdaForm.arity);
	assert(pos > 0); // cannot filter the MH arg itself
	assert(combinerType == combinerType.basicType());
	assert(combinerType.returnType() != void.class \|\| dropResult);

	BoundMethodHandle.SpeciesData oldData = oldSpeciesData();
	BoundMethodHandle.SpeciesData newData = newSpeciesData(L_TYPE);

	// The newly created LF will run with a different BMH.
	// Switch over any pre-existing BMH field references to the new BMH class.
	Name oldBaseAddress = lambdaForm.parameter(0); // BMH holding the values
	buf.replaceFunctions(oldData.getterFunctions(), newData.getterFunctions(), oldBaseAddress);
	Name newBaseAddress = oldBaseAddress.withConstraint(newData);
	buf.renameParameter(0, newBaseAddress);

	Name getCombiner = new Name(newData.getterFunction(oldData.fieldCount()), newBaseAddress);
	Object[] combinerArgs = new Object[1 + combinerArity];
	combinerArgs[0] = getCombiner;
	Name[] newParams;
	if (keepArguments) {
	newParams = new Name[0];
	System.arraycopy(lambdaForm.names, pos + resultArity,
	combinerArgs, 1, combinerArity);
	} else {
	newParams = new Name[combinerArity];
	BasicType[] newTypes = basicTypes(combinerType.parameterList());
	for (int i = 0; i < newTypes.length; i++) {
	newParams[i] = new Name(pos + i, newTypes[i]);
	}
	System.arraycopy(newParams, 0,
	combinerArgs, 1, combinerArity);
	}
	Name callCombiner = new Name(combinerType, combinerArgs);

	// insert the two new expressions
	int exprPos = lambdaForm.arity();
	buf.insertExpression(exprPos+0, getCombiner);
	buf.insertExpression(exprPos+1, callCombiner);

	// insert new arguments, if needed
	int argPos = pos + resultArity; // skip result parameter
	for (Name newParam : newParams) {
	buf.insertParameter(argPos++, newParam);
	}
	assert(buf.lastIndexOf(callCombiner) == exprPos+1+newParams.length);
	if (!dropResult) {
	buf.replaceParameterByCopy(pos, exprPos+1+newParams.length);
	}

	return buf.endEdit();
	}

	LambdaForm filterReturnForm(BasicType newType, boolean constantZero) {
	Transform.Kind kind = (constantZero ? Transform.Kind.FILTER_RETURN_TO_ZERO : Transform.Kind.FILTER_RETURN);
	Transform key = Transform.of(kind, newType.ordinal());
	LambdaForm form = getInCache(key);
	if (form != null) {
	assert(form.arity == lambdaForm.arity);
	assert(form.returnType() == newType);
	return form;
	}
	LambdaFormBuffer buf = buffer();
	buf.startEdit();

	int insPos = lambdaForm.names.length;
	Name callFilter;
	if (constantZero) {
	// Synthesize a constant zero value for the given type.
	if (newType == V_TYPE)
	callFilter = null;
	else
	callFilter = new Name(constantZero(newType));
	} else {
	BoundMethodHandle.SpeciesData oldData = oldSpeciesData();
	BoundMethodHandle.SpeciesData newData = newSpeciesData(L_TYPE);

	// The newly created LF will run with a different BMH.
	// Switch over any pre-existing BMH field references to the new BMH class.
	Name oldBaseAddress = lambdaForm.parameter(0); // BMH holding the values
	buf.replaceFunctions(oldData.getterFunctions(), newData.getterFunctions(), oldBaseAddress);
	Name newBaseAddress = oldBaseAddress.withConstraint(newData);
	buf.renameParameter(0, newBaseAddress);

	Name getFilter = new Name(newData.getterFunction(oldData.fieldCount()), newBaseAddress);
	buf.insertExpression(insPos++, getFilter);
	BasicType oldType = lambdaForm.returnType();
	if (oldType == V_TYPE) {
	MethodType filterType = MethodType.methodType(newType.basicTypeClass());
	callFilter = new Name(filterType, getFilter);
	} else {
	MethodType filterType = MethodType.methodType(newType.basicTypeClass(), oldType.basicTypeClass());
	callFilter = new Name(filterType, getFilter, lambdaForm.names[lambdaForm.result]);
	}
	}

	if (callFilter != null)
	buf.insertExpression(insPos++, callFilter);
	buf.setResult(callFilter);

	form = buf.endEdit();
	return putInCache(key, form);
	}

	LambdaForm foldArgumentsForm(int foldPos, boolean dropResult, MethodType combinerType) {
	int combinerArity = combinerType.parameterCount();
	Transform.Kind kind = (dropResult ? Transform.Kind.FOLD_ARGS_TO_VOID : Transform.Kind.FOLD_ARGS);
	Transform key = Transform.of(kind, foldPos, combinerArity);
	LambdaForm form = getInCache(key);
	if (form != null) {
	assert(form.arity == lambdaForm.arity - (kind == Transform.Kind.FOLD_ARGS ? 1 : 0));
	return form;
	}
	form = makeArgumentCombinationForm(foldPos, combinerType, true, dropResult);
	return putInCache(key, form);
	}

	LambdaForm permuteArgumentsForm(int skip, int[] reorder) {
	assert(skip == 1); // skip only the leading MH argument, names[0]
	int length = lambdaForm.names.length;
	int outArgs = reorder.length;
	int inTypes = 0;
	boolean nullPerm = true;
	for (int i = 0; i < reorder.length; i++) {
	int inArg = reorder[i];
	if (inArg != i) nullPerm = false;
	inTypes = Math.max(inTypes, inArg+1);
	}
	assert(skip + reorder.length == lambdaForm.arity);
	if (nullPerm) return lambdaForm; // do not bother to cache
	Transform key = Transform.of(Transform.Kind.PERMUTE_ARGS, reorder);
	LambdaForm form = getInCache(key);
	if (form != null) {
	assert(form.arity == skip+inTypes) : form;
	return form;
	}

	BasicType[] types = new BasicType[inTypes];
	for (int i = 0; i < outArgs; i++) {
	int inArg = reorder[i];
	types[inArg] = lambdaForm.names[skip + i].type;
	}
	assert (skip + outArgs == lambdaForm.arity);
	assert (permutedTypesMatch(reorder, types, lambdaForm.names, skip));
	int pos = 0;
	while (pos < outArgs && reorder[pos] == pos) {
	pos += 1;
	}
	Name[] names2 = new Name[length - outArgs + inTypes];
	System.arraycopy(lambdaForm.names, 0, names2, 0, skip + pos);
	int bodyLength = length - lambdaForm.arity;
	System.arraycopy(lambdaForm.names, skip + outArgs, names2, skip + inTypes, bodyLength);
	int arity2 = names2.length - bodyLength;
	int result2 = lambdaForm.result;
	if (result2 >= skip) {
	if (result2 < skip + outArgs) {
	result2 = reorder[result2 - skip] + skip;
	} else {
	result2 = result2 - outArgs + inTypes;
	}
	}
	for (int j = pos; j < outArgs; j++) {
	Name n = lambdaForm.names[skip + j];
	int i = reorder[j];
	Name n2 = names2[skip + i];
	if (n2 == null) {
	names2[skip + i] = n2 = new Name(types[i]);
	} else {
	assert (n2.type == types[i]);
	}
	for (int k = arity2; k < names2.length; k++) {
	names2[k] = names2[k].replaceName(n, n2);
	}
	}
	for (int i = skip + pos; i < arity2; i++) {
	if (names2[i] == null) {
	names2[i] = argument(i, types[i - skip]);
	}
	}
	for (int j = lambdaForm.arity; j < lambdaForm.names.length; j++) {
	int i = j - lambdaForm.arity + arity2;
	Name n = lambdaForm.names[j];
	Name n2 = names2[i];
	if (n != n2) {
	for (int k = i + 1; k < names2.length; k++) {
	names2[k] = names2[k].replaceName(n, n2);
	}
	}
	}

	form = new LambdaForm(lambdaForm.debugName, arity2, names2, result2);
	return putInCache(key, form);
	}

	static boolean permutedTypesMatch(int[] reorder, BasicType[] types, Name[] names, int skip) {
	for (int i = 0; i < reorder.length; i++) {
	assert (names[skip + i].isParam());
	assert (names[skip + i].type == types[reorder[i]]);
	}
	return true;
	}
	}

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