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 * Copyright (c) 2017, 2017, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 * 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.
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package com.oracle.graal.pointsto.flow;

import com.oracle.graal.pointsto.BigBang;
import com.oracle.graal.pointsto.meta.AnalysisField;
import com.oracle.graal.pointsto.typestate.TypeState;

The field filter flow is used for unsafe writes to fields. An unsafe write to an object can write
to any of the unsafe accessed fields of that object, however the written values may not be
compatible with all the fields. Thus the written values need to be filtered using the field
FieldFilterTypeFlow type. The FieldFilterTypeFlow is a simplified version of FilterTypeFlow in
that it is 'not-exact', i.e., it allows types of that are sub-types of the field declared type,
it is always 'assignable', i.e., it allows types that are assignable to the field declared type,
and it 'includes-null', i.e., it allows null values to pass through. However it's 'source' is an
AnalysisField and not a ValueNode, thus it's a completely different class.
/**
 * The field filter flow is used for unsafe writes to fields. An unsafe write to an object can write
 * to any of the unsafe accessed fields of that object, however the written values may not be
 * compatible with all the fields. Thus the written values need to be filtered using the field
 * FieldFilterTypeFlow type. The FieldFilterTypeFlow is a simplified version of FilterTypeFlow in
 * that it is 'not-exact', i.e., it allows types of that are sub-types of the field declared type,
 * it is always 'assignable', i.e., it allows types that are assignable to the field declared type,
 * and it 'includes-null', i.e., it allows null values to pass through. However it's 'source' is an
 * AnalysisField and not a ValueNode, thus it's a completely different class.
 */
public class FieldFilterTypeFlow extends TypeFlow<AnalysisField> {

    public FieldFilterTypeFlow(AnalysisField field) {
        super(field, field.getType());
    }

    @Override
    public TypeState filter(BigBang bb, TypeState update) {
        if (declaredType.equals(bb.getObjectType())) {
            /* No need to filter. */
            return update;
        } else {
            /* Filter the incoming state with the field type. */
            return TypeState.forIntersection(bb, update, declaredType.getTypeFlow(bb, true).getState());
        }
    }

    @Override
    protected void onInputSaturated(BigBang bb, TypeFlow<?> input) {
        setSaturated();
        /* Swap out this flow with its declared type flow. */
        swapOut(bb, declaredType.getTypeFlow(bb, true));
    }

    @Override
    public String toString() {
        return "FieldFilterTypeFlow<" + source + ">";
    }
}