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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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 * 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.
 *
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package com.oracle.svm.truffle;

import org.graalvm.compiler.core.common.spi.ConstantFieldProvider;
import org.graalvm.compiler.truffle.compiler.TruffleConstantFieldProvider;
import org.graalvm.nativeimage.Platform;
import org.graalvm.nativeimage.Platforms;

import com.oracle.graal.pointsto.meta.AnalysisField;
import com.oracle.truffle.api.CompilerDirectives.CompilationFinal;

import jdk.vm.ci.meta.ResolvedJavaField;

@Platforms(Platform.HOSTED_ONLY.class)
public final class HostedTruffleConstantFieldProvider implements ConstantFieldProvider {
    private final ConstantFieldProvider wrappedConstantFieldProvider;

    public HostedTruffleConstantFieldProvider(ConstantFieldProvider wrappedConstantFieldProvider) {
        this.wrappedConstantFieldProvider = wrappedConstantFieldProvider;
    }

    
The CompilationFinal annotation allows to mark arrays as stable so that array elements can be constant folded. However, this constant folding must not happen during native image generation: that would be too early since the array can still be modified before compilation. So we disable the constant folding of such fields when preparing graphs, so that during partial evaluation the TruffleConstantFieldProvider can do the correct constant folding that takes stable array dimensions into account. /**
     * The {@link CompilationFinal} annotation allows to mark arrays as stable so that array
     * elements can be constant folded. However, this constant folding must not happen during native
     * image generation: that would be too early since the array can still be modified before
     * compilation. So we disable the constant folding of such fields when preparing graphs, so that
     * during partial evaluation the {@link TruffleConstantFieldProvider} can do the correct
     * constant folding that takes stable array dimensions into account.
     */
    @Override
    public <T> T readConstantField(ResolvedJavaField field, ConstantFieldTool<T> tool) {
        if (field.getAnnotation(CompilationFinal.class) != null) {
            if (field instanceof AnalysisField) {
                /*
                 * If this is a final field, it might be constant folded in AOT compilation and also
                 * during static analysis. So the runtime graph can be the only place where a read
                 * occurs, therefore we explicitly mark the field as read.
                 */
                ((AnalysisField) field).registerAsRead(null);
            }
            return null;
        }

        return wrappedConstantFieldProvider.readConstantField(field, tool);
    }
}