ObjectFieldInfo.cpp

/*******************************************************************************
 * Copyright IBM Corp. and others 2015
 *
 * This program and the accompanying materials are made available under
 * the terms of the Eclipse Public License 2.0 which accompanies this
 * distribution and is available at https://www.eclipse.org/legal/epl-2.0/
 * or the Apache License, Version 2.0 which accompanies this distribution and
 * is available at https://www.apache.org/licenses/LICENSE-2.0.
 *
 * This Source Code may also be made available under the following
 * Secondary Licenses when the conditions for such availability set
 * forth in the Eclipse Public License, v. 2.0 are satisfied: GNU
 * General Public License, version 2 with the GNU Classpath
 * Exception [1] and GNU General Public License, version 2 with the
 * OpenJDK Assembly Exception [2].
 *
 * [1] https://www.gnu.org/software/classpath/license.html
 * [2] https://openjdk.org/legal/assembly-exception.html
 *
 * SPDX-License-Identifier: EPL-2.0 OR Apache-2.0 OR GPL-2.0-only WITH Classpath-exception-2.0 OR GPL-2.0-only WITH OpenJDK-assembly-exception-1.0
 *******************************************************************************/

#include "j9.h"
#include "j9comp.h"
#include "j9modifiers_api.h"
#include "ObjectFieldInfo.hpp"
#include "util_api.h"
#include "vm_api.h"

/**
 * Calculate the number of various types of fields.
 * Make a copy of the hidden fields.  The first element in the output array is the last added.
 * Only single fields and 32-bit object references are candidates for backfill.
 */
void
ObjectFieldInfo::countInstanceFields(void)
{
	struct J9ROMFieldWalkState fieldWalkState;

	memset(&fieldWalkState,0, sizeof(fieldWalkState));
	/* iterate over fields to count instance fields by size */

	J9ROMFieldShape *field = romFieldsStartDo(_romClass, &fieldWalkState);
	while (NULL != field) {
		const U_32 modifiers = field->modifiers;
		if (J9_ARE_NO_BITS_SET(modifiers, J9AccStatic) ) {
			if (modifiers & J9FieldFlagObject) {
#if defined(J9VM_OPT_VALHALLA_FLATTENABLE_VALUE_TYPES)
				if (J9_ARE_ALL_BITS_SET(modifiers, J9FieldFlagIsNullRestricted)) {
					J9UTF8 *fieldSig = J9ROMFIELDSHAPE_SIGNATURE(field);
					U_8 *fieldSigBytes = J9UTF8_DATA(J9ROMFIELDSHAPE_SIGNATURE(field));
					J9Class *fieldClass = findJ9ClassInFlattenedClassCache(_flattenedClassCache, fieldSigBytes + 1, J9UTF8_LENGTH(fieldSig) - 2);
					U_32 size = (U_32)fieldClass->totalInstanceSize;
					if (!J9_IS_FIELD_FLATTENED(fieldClass, field)) {
						_instanceObjectCount += 1;
						_totalObjectCount += 1;
					} else {
						bool forceDoubleAlignment = false;
						if (sizeof(U_32) == _referenceSize) {
							/* Flattened volatile valueType that is 8 bytes should be put at 8-byte aligned address. Currently flattening is disabled
							 * for such valueType > 8 bytes.
							 */
							forceDoubleAlignment = (J9_ARE_ALL_BITS_SET(field->modifiers, J9AccVolatile) && (sizeof(U_64) == J9CLASS_UNPADDED_INSTANCE_SIZE(fieldClass)));
						} else {
							/* copyObjectFields() uses U_64 load/store. Put all nested fields at 8-byte aligned address. */
							forceDoubleAlignment = true;
						}
						if (forceDoubleAlignment
							|| J9_ARE_ALL_BITS_SET(fieldClass->classFlags, J9ClassLargestAlignmentConstraintDouble)
						) {
							if (J9CLASS_HAS_4BYTE_PREPADDING(fieldClass)) {
								size -= sizeof(U_32);
							}
							_totalFlatFieldDoubleBytes += (U_32) ROUND_UP_TO_POWEROF2(size, sizeof(U_64));
						} else if (J9_ARE_ALL_BITS_SET(fieldClass->classFlags, J9ClassLargestAlignmentConstraintReference)) {
							size = (U_32) ROUND_UP_TO_POWEROF2(size, (UDATA)_referenceSize);
							_totalFlatFieldRefBytes += size;
							setPotentialFlatObjectInstanceBackfill(size);
						} else {
							_totalFlatFieldSingleBytes += size;
							setPotentialFlatSingleInstanceBackfill(size);
						}
					}
				} else
#endif /* J9VM_OPT_VALHALLA_FLATTENABLE_VALUE_TYPES */
				{
					_instanceObjectCount += 1;
					_totalObjectCount += 1;
				}
			} else if (modifiers & J9FieldSizeDouble) {
				_instanceDoubleCount += 1;
				_totalDoubleCount += 1;
			} else {
				_instanceSingleCount += 1;
				_totalSingleCount += 1;
			}
		}
		field = romFieldsNextDo(&fieldWalkState);
	}
	if (isContendedClassLayout()) { /* all instance fields are contended. Reassign them and fix the total counts */
		_contendedObjectCount = _instanceObjectCount;
		_totalObjectCount -= _instanceObjectCount;
		_instanceObjectCount = 0;
		_contendedDoubleCount = _instanceDoubleCount;
		_totalDoubleCount -= _instanceDoubleCount;
		_instanceDoubleCount = 0;
		_contendedSingleCount = _instanceSingleCount;
		_totalSingleCount -= _instanceSingleCount;
		_instanceSingleCount = 0;
	} else {
		_instanceFieldBackfillEligible = (_instanceSingleCount > 0) || (_objectCanUseBackfill && (_instanceSingleCount > 0));
	}
}

U_32
ObjectFieldInfo::countAndCopyHiddenFields(J9HiddenInstanceField *hiddenFieldList, J9HiddenInstanceField *hiddenFieldArray[])
{
	const J9UTF8 *className = J9ROMCLASS_CLASSNAME(_romClass);

	_hiddenFieldCount = 0;
	for (J9HiddenInstanceField *hiddenField = hiddenFieldList; NULL != hiddenField; hiddenField = hiddenField->next) {
		if ((NULL == hiddenField->className) || J9UTF8_EQUALS(hiddenField->className, className)) {
			const U_32 modifiers = hiddenField->shape->modifiers;
			const bool thisFieldUnresolved = ((UDATA)-1 == hiddenField->fieldOffset);

			_hiddenFieldOffsetResolutionRequired |= thisFieldUnresolved;
			if (J9_ARE_ANY_BITS_SET(modifiers, J9FieldFlagObject)) {
				_totalObjectCount += 1;
			} else if (J9_ARE_ANY_BITS_SET(modifiers, J9FieldSizeDouble)) {
				_totalDoubleCount += 1;
			} else {
				_totalSingleCount += 1;
			}
			hiddenFieldArray[_hiddenFieldCount] = hiddenField;
			_hiddenFieldCount += 1;
		}
	}
	return _hiddenFieldCount;
}

U_32
ObjectFieldInfo::calculateTotalFieldsSizeAndBackfill()
{
	U_32 accumulator = 0;
	if (isContendedClassLayout()) {
		_superclassBackfillOffset = NO_BACKFILL_AVAILABLE;
		_myBackfillOffset = NO_BACKFILL_AVAILABLE;
		_subclassBackfillOffset = NO_BACKFILL_AVAILABLE;

		accumulator = getPaddedTrueNonContendedSize(); /* this includes the header */
		accumulator += (_contendedObjectCount * _referenceSize) + (_contendedSingleCount * sizeof(U_32)) + (_contendedDoubleCount * sizeof(U_64)); /* add the contended fields */
		accumulator = ROUND_UP_TO_POWEROF2((UDATA)accumulator, (UDATA)_cacheLineSize) - _objectHeaderSize; /* Rounding takes care of the odd number of 4-byte fields. Remove the header */
	} else {
		accumulator = _superclassFieldsSize + (_totalObjectCount * _referenceSize) + (_totalSingleCount * sizeof(U_32)) + (_totalDoubleCount * sizeof(U_64));
#if defined(J9VM_OPT_VALHALLA_FLATTENABLE_VALUE_TYPES)
		accumulator += _totalFlatFieldDoubleBytes + _totalFlatFieldRefBytes + _totalFlatFieldSingleBytes;

		/* ValueTypes cannot be subtyped and their superClass contains no fields */
		if (!isValue()) {
#endif /* J9VM_OPT_VALHALLA_FLATTENABLE_VALUE_TYPES */
			/* if the superclass is not end aligned but we have doubleword fields, use the space before the first field as the backfill */
			if (
					((getSuperclassObjectSize() % OBJECT_SIZE_INCREMENT_IN_BYTES) != 0) && /* superclass is not end-aligned */
					((_totalDoubleCount > 0) || (!_objectCanUseBackfill && (_totalObjectCount > 0)))
			){ /* our fields start on a 8-byte boundary */
				Assert_VM_equal(_superclassBackfillOffset, NO_BACKFILL_AVAILABLE);
				_superclassBackfillOffset = getSuperclassFieldsSize();
				accumulator += BACKFILL_SIZE;
			}
			if (isSuperclassBackfillSlotAvailable() && isBackfillSuitableFieldAvailable()) {
				accumulator -= BACKFILL_SIZE;
				_myBackfillOffset = _superclassBackfillOffset;
				_superclassBackfillOffset = NO_BACKFILL_AVAILABLE;
			}
			if (((accumulator + _objectHeaderSize) % OBJECT_SIZE_INCREMENT_IN_BYTES) != 0) {
				/* we have consumed the superclass's backfill (if any), so let our subclass use the residue at the end of this class. */
				_subclassBackfillOffset = accumulator;
				accumulator += BACKFILL_SIZE;
			} else {
				_subclassBackfillOffset = _superclassBackfillOffset;
			}
#if defined(J9VM_OPT_VALHALLA_FLATTENABLE_VALUE_TYPES)
		} else {
			/* If the first field does not start at zero, this means we added padding to satisfy
			 * alignment requirements of double slot fields. We will use the J9ClassHasPrePadding flag
			 * to denote this.
			 */
			U_32 firstFieldOffset = calculateFieldDataStart();
			if (0 < firstFieldOffset) {
				if (isBackfillSuitableFieldAvailable()) {
					/*
					 * If the class is a valuetype and it has at least one single or object aligned field, instead of pre-padding
					 * the field with the smaller alignment constraint will be placed first.
					 */
					_myBackfillOffset = 0;

					/*
					 * Backfill may not be end-aligned, ie 8, 16, 24btye types since  backfill begins on a (4 == offset %8) boundary.
					 * In these cases the types are post-padded so doubles can start on a 8byte boundary.
					 */
					if (isBackFillPostPadded()) {
						accumulator += BACKFILL_SIZE;
					}
				} else {
					/* Add pre-padding, firstFieldOffset can only be 4bytes here */
					accumulator += firstFieldOffset;
					setClassRequiresPrePadding();
				}
			}
		}
#endif /* J9VM_OPT_VALHALLA_FLATTENABLE_VALUE_TYPES */
	}
	return accumulator;
}