ci/hotspot/HotSpotConstantPool.java

/*
 * Copyright (c) 2011, 2015, 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.
 *
 * 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 jdk.vm.ci.hotspot;

import static jdk.vm.ci.hotspot.CompilerToVM.compilerToVM;
import static jdk.vm.ci.hotspot.HotSpotJVMCIRuntime.runtime;
import static jdk.vm.ci.hotspot.HotSpotVMConfig.config;
import static jdk.vm.ci.hotspot.UnsafeAccess.UNSAFE;

import java.lang.invoke.MethodHandle;

import jdk.vm.ci.common.JVMCIError;
import jdk.vm.ci.meta.ConstantPool;
import jdk.vm.ci.meta.JavaConstant;
import jdk.vm.ci.meta.JavaField;
import jdk.vm.ci.meta.JavaMethod;
import jdk.vm.ci.meta.JavaType;
import jdk.vm.ci.meta.ResolvedJavaMethod;
import jdk.vm.ci.meta.ResolvedJavaType;
import jdk.vm.ci.meta.Signature;

/**
 * Implementation of {@link ConstantPool} for HotSpot.
 */
final class HotSpotConstantPool implements ConstantPool, MetaspaceWrapperObject {

    /**
     * Subset of JVM bytecode opcodes used by {@link HotSpotConstantPool}.
     */
    public static class Bytecodes {
        public static final int LDC = 18; // 0x12
        public static final int LDC_W = 19; // 0x13
        public static final int LDC2_W = 20; // 0x14
        public static final int GETSTATIC = 178; // 0xB2
        public static final int PUTSTATIC = 179; // 0xB3
        public static final int GETFIELD = 180; // 0xB4
        public static final int PUTFIELD = 181; // 0xB5
        public static final int INVOKEVIRTUAL = 182; // 0xB6
        public static final int INVOKESPECIAL = 183; // 0xB7
        public static final int INVOKESTATIC = 184; // 0xB8
        public static final int INVOKEINTERFACE = 185; // 0xB9
        public static final int INVOKEDYNAMIC = 186; // 0xBA
        public static final int NEW = 187; // 0xBB
        public static final int NEWARRAY = 188; // 0xBC
        public static final int ANEWARRAY = 189; // 0xBD
        public static final int CHECKCAST = 192; // 0xC0
        public static final int INSTANCEOF = 193; // 0xC1
        public static final int MULTIANEWARRAY = 197; // 0xC5

        static boolean isInvoke(int opcode) {
            switch (opcode) {
                case INVOKEVIRTUAL:
                case INVOKESPECIAL:
                case INVOKESTATIC:
                case INVOKEINTERFACE:
                case INVOKEDYNAMIC:
                    return true;
                default:
                    return false;
            }
        }

        /**
         * See: {@code Rewriter::maybe_rewrite_invokehandle}.
         */
        static boolean isInvokeHandleAlias(int opcode) {
            switch (opcode) {
                case INVOKEVIRTUAL:
                case INVOKESPECIAL:
                    return true;
                default:
                    return false;
            }
        }
    }

    /**
     * Enum of all {@code JVM_CONSTANT} constants used in the VM. This includes the public and
     * internal ones.
     */
    private enum JVM_CONSTANT {
        // @formatter:off
        Utf8(config().jvmConstantUtf8),
        Integer(config().jvmConstantInteger),
        Long(config().jvmConstantLong),
        Float(config().jvmConstantFloat),
        Double(config().jvmConstantDouble),
        Class(config().jvmConstantClass),
        UnresolvedClass(config().jvmConstantUnresolvedClass),
        UnresolvedClassInError(config().jvmConstantUnresolvedClassInError),
        String(config().jvmConstantString),
        Fieldref(config().jvmConstantFieldref),
        MethodRef(config().jvmConstantMethodref),
        InterfaceMethodref(config().jvmConstantInterfaceMethodref),
        NameAndType(config().jvmConstantNameAndType),
        MethodHandle(config().jvmConstantMethodHandle),
        MethodHandleInError(config().jvmConstantMethodHandleInError),
        MethodType(config().jvmConstantMethodType),
        MethodTypeInError(config().jvmConstantMethodTypeInError),
        InvokeDynamic(config().jvmConstantInvokeDynamic);
        // @formatter:on

        private final int tag;

        private static final int ExternalMax = config().jvmConstantExternalMax;
        private static final int InternalMin = config().jvmConstantInternalMin;
        private static final int InternalMax = config().jvmConstantInternalMax;

        JVM_CONSTANT(int tag) {
            this.tag = tag;
        }

        /**
         * Maps JVM_CONSTANT tags to {@link JVM_CONSTANT} values. Using a separate class for lazy
         * initialization.
         */
        static class TagValueMap {
            private static final JVM_CONSTANT[] table = new JVM_CONSTANT[ExternalMax + 1 + (InternalMax - InternalMin) + 1];

            static {
                assert InternalMin > ExternalMax;
                for (JVM_CONSTANT e : values()) {
                    table[indexOf(e.tag)] = e;
                }
            }

            private static int indexOf(int tag) {
                if (tag >= InternalMin) {
                    return tag - InternalMin + ExternalMax + 1;
                } else {
                    assert tag <= ExternalMax;
                }
                return tag;
            }

            static JVM_CONSTANT get(int tag) {
                JVM_CONSTANT res = table[indexOf(tag)];
                if (res != null) {
                    return res;
                }
                throw new JVMCIError("Unknown JVM_CONSTANT tag %s", tag);
            }
        }

        public static JVM_CONSTANT getEnum(int tag) {
            return TagValueMap.get(tag);
        }
    }

    private static class LookupTypeCacheElement {
        int lastCpi = Integer.MIN_VALUE;
        JavaType javaType;

        LookupTypeCacheElement(int lastCpi, JavaType javaType) {
            super();
            this.lastCpi = lastCpi;
            this.javaType = javaType;
        }
    }

    /**
     * Reference to the C++ ConstantPool object.
     */
    private final long metaspaceConstantPool;
    private volatile LookupTypeCacheElement lastLookupType;

    /**
     * Gets the JVMCI mirror from a HotSpot constant pool.The VM is responsible for ensuring that
     * the ConstantPool is kept alive for the duration of this call and the
     * {@link HotSpotJVMCIMetaAccessContext} keeps it alive after that.
     *
     * Called from the VM.
     *
     * @param metaspaceConstantPool a metaspace ConstantPool object
     * @return the {@link HotSpotConstantPool} corresponding to {@code metaspaceConstantPool}
     */
    @SuppressWarnings("unused")
    private static HotSpotConstantPool fromMetaspace(long metaspaceConstantPool) {
        HotSpotConstantPool cp = new HotSpotConstantPool(metaspaceConstantPool);
        runtime().metaAccessContext.add(cp);
        return cp;
    }

    private HotSpotConstantPool(long metaspaceConstantPool) {
        this.metaspaceConstantPool = metaspaceConstantPool;
    }

    /**
     * Gets the holder for this constant pool as {@link HotSpotResolvedObjectTypeImpl}.
     *
     * @return holder for this constant pool
     */
    private HotSpotResolvedObjectType getHolder() {
        return compilerToVM().getResolvedJavaType(this, config().constantPoolHolderOffset, false);
    }

    /**
     * Converts a raw index from the bytecodes to a constant pool index by adding a
     * {@link HotSpotVMConfig#constantPoolCpCacheIndexTag constant}.
     *
     * @param rawIndex index from the bytecode
     * @param opcode bytecode to convert the index for
     * @return constant pool index
     */
    private static int rawIndexToConstantPoolIndex(int rawIndex, int opcode) {
        int index;
        if (opcode == Bytecodes.INVOKEDYNAMIC) {
            index = rawIndex;
            // See: ConstantPool::is_invokedynamic_index
            assert index < 0 : "not an invokedynamic constant pool index " + index;
        } else {
            assert opcode == Bytecodes.GETFIELD || opcode == Bytecodes.PUTFIELD || opcode == Bytecodes.GETSTATIC || opcode == Bytecodes.PUTSTATIC || opcode == Bytecodes.INVOKEINTERFACE ||
                            opcode == Bytecodes.INVOKEVIRTUAL || opcode == Bytecodes.INVOKESPECIAL || opcode == Bytecodes.INVOKESTATIC : "unexpected invoke opcode " + opcode;
            index = rawIndex + config().constantPoolCpCacheIndexTag;
        }
        return index;
    }

    /**
     * Decode a constant pool cache index to a constant pool index.
     *
     * See {@code ConstantPool::decode_cpcache_index}.
     *
     * @param index constant pool cache index
     * @return decoded index
     */
    private static int decodeConstantPoolCacheIndex(int index) {
        if (isInvokedynamicIndex(index)) {
            return decodeInvokedynamicIndex(index);
        } else {
            return index - config().constantPoolCpCacheIndexTag;
        }
    }

    /**
     * See {@code ConstantPool::is_invokedynamic_index}.
     */
    private static boolean isInvokedynamicIndex(int index) {
        return index < 0;
    }

    /**
     * See {@code ConstantPool::decode_invokedynamic_index}.
     */
    private static int decodeInvokedynamicIndex(int i) {
        assert isInvokedynamicIndex(i) : i;
        return ~i;
    }

    long getMetaspaceConstantPool() {
        return metaspaceConstantPool;
    }

    public long getMetaspacePointer() {
        return getMetaspaceConstantPool();
    }

    /**
     * Gets the constant pool tag at index {@code index}.
     *
     * @param index constant pool index
     * @return constant pool tag
     */
    private JVM_CONSTANT getTagAt(int index) {
        assert checkBounds(index);
        HotSpotVMConfig config = config();
        final long metaspaceConstantPoolTags = UNSAFE.getAddress(getMetaspaceConstantPool() + config.constantPoolTagsOffset);
        final int tag = UNSAFE.getByteVolatile(null, metaspaceConstantPoolTags + config.arrayU1DataOffset + index);
        if (tag == 0) {
            return null;
        }
        return JVM_CONSTANT.getEnum(tag);
    }

    /**
     * Gets the constant pool entry at index {@code index}.
     *
     * @param index constant pool index
     * @return constant pool entry
     */
    long getEntryAt(int index) {
        assert checkBounds(index);
        int offset = index * runtime().getHostJVMCIBackend().getTarget().wordSize;
        return UNSAFE.getAddress(getMetaspaceConstantPool() + config().constantPoolSize + offset);
    }

    /**
     * Gets the integer constant pool entry at index {@code index}.
     *
     * @param index constant pool index
     * @return integer constant pool entry at index
     */
    private int getIntAt(int index) {
        assert checkTag(index, JVM_CONSTANT.Integer);
        int offset = index * runtime().getHostJVMCIBackend().getTarget().wordSize;
        return UNSAFE.getInt(getMetaspaceConstantPool() + config().constantPoolSize + offset);
    }

    /**
     * Gets the long constant pool entry at index {@code index}.
     *
     * @param index constant pool index
     * @return long constant pool entry
     */
    private long getLongAt(int index) {
        assert checkTag(index, JVM_CONSTANT.Long);
        int offset = index * runtime().getHostJVMCIBackend().getTarget().wordSize;
        return UNSAFE.getLong(getMetaspaceConstantPool() + config().constantPoolSize + offset);
    }

    /**
     * Gets the float constant pool entry at index {@code index}.
     *
     * @param index constant pool index
     * @return float constant pool entry
     */
    private float getFloatAt(int index) {
        assert checkTag(index, JVM_CONSTANT.Float);
        int offset = index * runtime().getHostJVMCIBackend().getTarget().wordSize;
        return UNSAFE.getFloat(getMetaspaceConstantPool() + config().constantPoolSize + offset);
    }

    /**
     * Gets the double constant pool entry at index {@code index}.
     *
     * @param index constant pool index
     * @return float constant pool entry
     */
    private double getDoubleAt(int index) {
        assert checkTag(index, JVM_CONSTANT.Double);
        int offset = index * runtime().getHostJVMCIBackend().getTarget().wordSize;
        return UNSAFE.getDouble(getMetaspaceConstantPool() + config().constantPoolSize + offset);
    }

    /**
     * Gets the {@code JVM_CONSTANT_NameAndType} constant pool entry at index {@code index}.
     *
     * @param index constant pool index
     * @return {@code JVM_CONSTANT_NameAndType} constant pool entry
     */
    private int getNameAndTypeAt(int index) {
        assert checkTag(index, JVM_CONSTANT.NameAndType);
        int offset = index * runtime().getHostJVMCIBackend().getTarget().wordSize;
        return UNSAFE.getInt(getMetaspaceConstantPool() + config().constantPoolSize + offset);
    }

    /**
     * Gets the {@code JVM_CONSTANT_NameAndType} reference index constant pool entry at index
     * {@code index}.
     *
     * @param index constant pool index
     * @return {@code JVM_CONSTANT_NameAndType} reference constant pool entry
     */
    private int getNameAndTypeRefIndexAt(int index) {
        return compilerToVM().lookupNameAndTypeRefIndexInPool(this, index);
    }

    /**
     * Gets the name of a {@code JVM_CONSTANT_NameAndType} constant pool entry referenced by another
     * entry denoted by {@code which}.
     *
     * @param which constant pool index or constant pool cache index
     * @return name as {@link String}
     */
    private String getNameOf(int which) {
        return compilerToVM().lookupNameInPool(this, which);
    }

    /**
     * Gets the name reference index of a {@code JVM_CONSTANT_NameAndType} constant pool entry at
     * index {@code index}.
     *
     * @param index constant pool index
     * @return name reference index
     */
    private int getNameRefIndexAt(int index) {
        final int refIndex = getNameAndTypeAt(index);
        // name ref index is in the low 16-bits.
        return refIndex & 0xFFFF;
    }

    /**
     * Gets the signature of a {@code JVM_CONSTANT_NameAndType} constant pool entry referenced by
     * another entry denoted by {@code which}.
     *
     * @param which constant pool index or constant pool cache index
     * @return signature as {@link String}
     */
    private String getSignatureOf(int which) {
        return compilerToVM().lookupSignatureInPool(this, which);
    }

    /**
     * Gets the signature reference index of a {@code JVM_CONSTANT_NameAndType} constant pool entry
     * at index {@code index}.
     *
     * @param index constant pool index
     * @return signature reference index
     */
    private int getSignatureRefIndexAt(int index) {
        final int refIndex = getNameAndTypeAt(index);
        // signature ref index is in the high 16-bits.
        return refIndex >>> 16;
    }

    /**
     * Gets the klass reference index constant pool entry at index {@code index}.
     *
     * @param index constant pool index
     * @return klass reference index
     */
    private int getKlassRefIndexAt(int index) {
        return compilerToVM().lookupKlassRefIndexInPool(this, index);
    }

    /**
     * Gets the uncached klass reference index constant pool entry at index {@code index}. See:
     * {@code ConstantPool::uncached_klass_ref_index_at}.
     *
     * @param index constant pool index
     * @return klass reference index
     */
    private int getUncachedKlassRefIndexAt(int index) {
        assert checkTagIsFieldOrMethod(index);
        int offset = index * runtime().getHostJVMCIBackend().getTarget().wordSize;
        final int refIndex = UNSAFE.getInt(getMetaspaceConstantPool() + config().constantPoolSize + offset);
        // klass ref index is in the low 16-bits.
        return refIndex & 0xFFFF;
    }

    /**
     * Checks that the constant pool index {@code index} is in the bounds of the constant pool.
     *
     * @param index constant pool index
     * @throws AssertionError if the check fails
     */
    private boolean checkBounds(int index) {
        assert 0 <= index && index < length() : "index " + index + " not between 0 and " + length();
        return true;
    }

    /**
     * Checks that the constant pool tag at index {@code index} is equal to {@code tag}.
     *
     * @param index constant pool index
     * @param tag expected tag
     * @throws AssertionError if the check fails
     */
    private boolean checkTag(int index, JVM_CONSTANT tag) {
        final JVM_CONSTANT tagAt = getTagAt(index);
        assert tagAt == tag : "constant pool tag at index " + index + " is " + tagAt + " but expected " + tag;
        return true;
    }

    /**
     * Asserts that the constant pool tag at index {@code index} is a {@link JVM_CONSTANT#Fieldref},
     * or a {@link JVM_CONSTANT#MethodRef}, or a {@link JVM_CONSTANT#InterfaceMethodref}.
     *
     * @param index constant pool index
     * @throws AssertionError if the check fails
     */
    private boolean checkTagIsFieldOrMethod(int index) {
        final JVM_CONSTANT tagAt = getTagAt(index);
        assert tagAt == JVM_CONSTANT.Fieldref || tagAt == JVM_CONSTANT.MethodRef || tagAt == JVM_CONSTANT.InterfaceMethodref : tagAt;
        return true;
    }

    @Override
    public int length() {
        return UNSAFE.getInt(getMetaspaceConstantPool() + config().constantPoolLengthOffset);
    }

    @Override
    public Object lookupConstant(int cpi) {
        assert cpi != 0;
        final JVM_CONSTANT tag = getTagAt(cpi);
        switch (tag) {
            case Integer:
                return JavaConstant.forInt(getIntAt(cpi));
            case Long:
                return JavaConstant.forLong(getLongAt(cpi));
            case Float:
                return JavaConstant.forFloat(getFloatAt(cpi));
            case Double:
                return JavaConstant.forDouble(getDoubleAt(cpi));
            case Class:
            case UnresolvedClass:
            case UnresolvedClassInError:
                final int opcode = -1;  // opcode is not used
                return lookupType(cpi, opcode);
            case String:
                /*
                 * Normally, we would expect a String here, but anonymous classes can have
                 * "pseudo strings" (arbitrary live objects) patched into a String entry. Such
                 * entries do not have a symbol in the constant pool slot.
                 */
                Object string = compilerToVM().resolvePossiblyCachedConstantInPool(this, cpi);
                return HotSpotObjectConstantImpl.forObject(string);
            case MethodHandle:
            case MethodHandleInError:
            case MethodType:
            case MethodTypeInError:
                Object obj = compilerToVM().resolveConstantInPool(this, cpi);
                return HotSpotObjectConstantImpl.forObject(obj);
            default:
                throw new JVMCIError("Unknown constant pool tag %s", tag);
        }
    }

    @Override
    public String lookupUtf8(int cpi) {
        assert checkTag(cpi, JVM_CONSTANT.Utf8);
        return compilerToVM().getSymbol(getEntryAt(cpi));
    }

    @Override
    public Signature lookupSignature(int cpi) {
        return new HotSpotSignature(runtime(), lookupUtf8(cpi));
    }

    @Override
    public JavaConstant lookupAppendix(int cpi, int opcode) {
        assert Bytecodes.isInvoke(opcode);
        final int index = rawIndexToConstantPoolIndex(cpi, opcode);
        Object appendix = compilerToVM().lookupAppendixInPool(this, index);
        if (appendix == null) {
            return null;
        } else {
            return HotSpotObjectConstantImpl.forObject(appendix);
        }
    }

    /**
     * Gets a {@link JavaType} corresponding a given resolved or unresolved type.
     *
     * @param type either a ResolvedJavaType or a String naming a unresolved type.
     */
    private static JavaType getJavaType(final Object type) {
        if (type instanceof String) {
            String name = (String) type;
            return HotSpotUnresolvedJavaType.create(runtime(), "L" + name + ";");
        } else {
            return (JavaType) type;
        }
    }

    @Override
    public JavaMethod lookupMethod(int cpi, int opcode) {
        final int index = rawIndexToConstantPoolIndex(cpi, opcode);
        final HotSpotResolvedJavaMethod method = compilerToVM().lookupMethodInPool(this, index, (byte) opcode);
        if (method != null) {
            return method;
        } else {
            // Get the method's name and signature.
            String name = getNameOf(index);
            HotSpotSignature signature = new HotSpotSignature(runtime(), getSignatureOf(index));
            if (opcode == Bytecodes.INVOKEDYNAMIC) {
                HotSpotResolvedObjectType holder = HotSpotResolvedObjectTypeImpl.fromObjectClass(MethodHandle.class);
                return new HotSpotMethodUnresolved(name, signature, holder);
            } else {
                final int klassIndex = getKlassRefIndexAt(index);
                final Object type = compilerToVM().lookupKlassInPool(this, klassIndex);
                JavaType holder = getJavaType(type);
                return new HotSpotMethodUnresolved(name, signature, holder);
            }
        }
    }

    @Override
    public JavaType lookupType(int cpi, int opcode) {
        final LookupTypeCacheElement elem = this.lastLookupType;
        if (elem != null && elem.lastCpi == cpi) {
            return elem.javaType;
        } else {
            final Object type = compilerToVM().lookupKlassInPool(this, cpi);
            JavaType result = getJavaType(type);
            if (result instanceof ResolvedJavaType) {
                this.lastLookupType = new LookupTypeCacheElement(cpi, result);
            }
            return result;
        }
    }

    @Override
    public JavaField lookupField(int cpi, ResolvedJavaMethod method, int opcode) {
        final int index = rawIndexToConstantPoolIndex(cpi, opcode);
        final int nameAndTypeIndex = getNameAndTypeRefIndexAt(index);
        final int typeIndex = getSignatureRefIndexAt(nameAndTypeIndex);
        String typeName = lookupUtf8(typeIndex);
        JavaType type = runtime().lookupType(typeName, getHolder(), false);

        final int holderIndex = getKlassRefIndexAt(index);
        JavaType holder = lookupType(holderIndex, opcode);

        if (holder instanceof HotSpotResolvedObjectTypeImpl) {
            int[] info = new int[3];
            HotSpotResolvedObjectTypeImpl resolvedHolder;
            try {
                resolvedHolder = compilerToVM().resolveFieldInPool(this, index, (HotSpotResolvedJavaMethodImpl) method, (byte) opcode, info);
            } catch (Throwable t) {
                /*
                 * If there was an exception resolving the field we give up and return an unresolved
                 * field.
                 */
                return new HotSpotUnresolvedField(holder, lookupUtf8(getNameRefIndexAt(nameAndTypeIndex)), type);
            }
            final int flags = info[0];
            final int offset = info[1];
            final int fieldIndex = info[2];
            HotSpotResolvedJavaField result = resolvedHolder.createField(type, offset, flags, fieldIndex);
            return result;
        } else {
            return new HotSpotUnresolvedField(holder, lookupUtf8(getNameRefIndexAt(nameAndTypeIndex)), type);
        }
    }

    @Override
    @SuppressWarnings("fallthrough")
    public void loadReferencedType(int cpi, int opcode) {
        int index;
        switch (opcode) {
            case Bytecodes.CHECKCAST:
            case Bytecodes.INSTANCEOF:
            case Bytecodes.NEW:
            case Bytecodes.ANEWARRAY:
            case Bytecodes.MULTIANEWARRAY:
            case Bytecodes.LDC:
            case Bytecodes.LDC_W:
            case Bytecodes.LDC2_W:
                index = cpi;
                break;
            case Bytecodes.INVOKEDYNAMIC: {
                // invokedynamic instructions point to a constant pool cache entry.
                index = decodeConstantPoolCacheIndex(cpi) + config().constantPoolCpCacheIndexTag;
                index = compilerToVM().constantPoolRemapInstructionOperandFromCache(this, index);
                break;
            }
            case Bytecodes.GETSTATIC:
            case Bytecodes.PUTSTATIC:
            case Bytecodes.GETFIELD:
            case Bytecodes.PUTFIELD:
            case Bytecodes.INVOKEVIRTUAL:
            case Bytecodes.INVOKESPECIAL:
            case Bytecodes.INVOKESTATIC:
            case Bytecodes.INVOKEINTERFACE: {
                // invoke and field instructions point to a constant pool cache entry.
                index = rawIndexToConstantPoolIndex(cpi, opcode);
                index = compilerToVM().constantPoolRemapInstructionOperandFromCache(this, index);
                break;
            }
            default:
                throw JVMCIError.shouldNotReachHere("Unexpected opcode " + opcode);
        }

        final JVM_CONSTANT tag = getTagAt(index);
        if (tag == null) {
            assert getTagAt(index - 1) == JVM_CONSTANT.Double || getTagAt(index - 1) == JVM_CONSTANT.Long;
            return;
        }
        switch (tag) {
            case MethodRef:
            case Fieldref:
            case InterfaceMethodref:
                index = getUncachedKlassRefIndexAt(index);
                // Read the tag only once because it could change between multiple reads.
                final JVM_CONSTANT klassTag = getTagAt(index);
                assert klassTag == JVM_CONSTANT.Class || klassTag == JVM_CONSTANT.UnresolvedClass || klassTag == JVM_CONSTANT.UnresolvedClassInError : klassTag;
                // fall through
            case Class:
            case UnresolvedClass:
            case UnresolvedClassInError:
                final HotSpotResolvedObjectTypeImpl type = compilerToVM().resolveTypeInPool(this, index);
                Class<?> klass = type.mirror();
                if (!klass.isPrimitive() && !klass.isArray()) {
                    UNSAFE.ensureClassInitialized(klass);
                }
                if (tag == JVM_CONSTANT.MethodRef) {
                    if (Bytecodes.isInvokeHandleAlias(opcode) && isSignaturePolymorphicHolder(type)) {
                        final int methodRefCacheIndex = rawIndexToConstantPoolIndex(cpi, opcode);
                        assert checkTag(compilerToVM().constantPoolRemapInstructionOperandFromCache(this, methodRefCacheIndex), JVM_CONSTANT.MethodRef);
                        compilerToVM().resolveInvokeHandleInPool(this, methodRefCacheIndex);
                    }
                }

                break;
            case InvokeDynamic:
                if (isInvokedynamicIndex(cpi)) {
                    compilerToVM().resolveInvokeDynamicInPool(this, cpi);
                }
                break;
            default:
                // nothing
                break;
        }

    }

    // Lazily initialized.
    private static String[] signaturePolymorphicHolders;

    /**
     * Determines if {@code type} contains signature polymorphic methods.
     */
    static boolean isSignaturePolymorphicHolder(final ResolvedJavaType type) {
        String name = type.getName();
        if (signaturePolymorphicHolders == null) {
            signaturePolymorphicHolders = compilerToVM().getSignaturePolymorphicHolders();
        }
        for (String holder : signaturePolymorphicHolders) {
            if (name.equals(holder)) {
                return true;
            }
        }
        return false;
    }

    @Override
    public String toString() {
        HotSpotResolvedObjectType holder = getHolder();
        return "HotSpotConstantPool<" + holder.toJavaName() + ">";
    }
}