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/*
* Copyright (C) 2018-2019 Apple Inc. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
* EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR
* CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
* EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
* PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
* PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
* OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
#pragma once
namespace JSC {
enum class GetByIdMode : uint8_t {
ProtoLoad = 0, // This must be zero to reuse the higher bits of the pointer as this ProtoLoad mode.
Default = 1,
Unset = 2,
ArrayLength = 3,
};
struct GetByIdModeMetadataDefault {
StructureID structureID;
PropertyOffset cachedOffset;
unsigned padding1;
};
static_assert(sizeof(GetByIdModeMetadataDefault) == 12);
struct GetByIdModeMetadataUnset {
StructureID structureID;
unsigned padding1;
unsigned padding2;
};
static_assert(sizeof(GetByIdModeMetadataUnset) == 12);
struct GetByIdModeMetadataArrayLength {
unsigned padding1;
unsigned padding2;
unsigned padding3;
};
static_assert(sizeof(GetByIdModeMetadataArrayLength) == 12);
struct GetByIdModeMetadataProtoLoad {
StructureID structureID;
PropertyOffset cachedOffset;
JSObject* cachedSlot;
};
#if CPU(LITTLE_ENDIAN) && CPU(ADDRESS64)
static_assert(sizeof(GetByIdModeMetadataProtoLoad) == 16);
#endif
// In 64bit Little endian architecture, this union shares ProtoLoad's JSObject* cachedSlot with "hitCountForLLIntCaching" and "mode".
// This is possible because these values must be zero if we use ProtoLoad mode.
#if CPU(LITTLE_ENDIAN) && CPU(ADDRESS64)
union GetByIdModeMetadata {
GetByIdModeMetadata()
{
defaultMode.structureID = StructureID();
defaultMode.cachedOffset = 0;
defaultMode.padding1 = 0;
mode = GetByIdMode::Default;
hitCountForLLIntCaching = Options::prototypeHitCountForLLIntCaching();
}
void clearToDefaultModeWithoutCache();
void setUnsetMode(Structure*);
void setArrayLengthMode();
void setProtoLoadMode(Structure*, PropertyOffset, JSObject*);
struct {
uint32_t padding1;
uint32_t padding2;
uint32_t padding3;
uint16_t padding4;
GetByIdMode mode;
uint8_t hitCountForLLIntCaching; // This must be zero when we use ProtoLoad mode.
};
static constexpr ptrdiff_t offsetOfMode() { return OBJECT_OFFSETOF(GetByIdModeMetadata, mode); }
GetByIdModeMetadataDefault defaultMode;
GetByIdModeMetadataUnset unsetMode;
GetByIdModeMetadataArrayLength arrayLengthMode;
GetByIdModeMetadataProtoLoad protoLoadMode;
};
static_assert(sizeof(GetByIdModeMetadata) == 16);
#else
struct GetByIdModeMetadata {
GetByIdModeMetadata()
{
defaultMode.structureID = StructureID();
defaultMode.cachedOffset = 0;
defaultMode.padding1 = 0;
mode = GetByIdMode::Default;
hitCountForLLIntCaching = Options::prototypeHitCountForLLIntCaching();
}
void clearToDefaultModeWithoutCache();
void setUnsetMode(Structure*);
void setArrayLengthMode();
void setProtoLoadMode(Structure*, PropertyOffset, JSObject*);
union {
GetByIdModeMetadataDefault defaultMode;
GetByIdModeMetadataUnset unsetMode;
GetByIdModeMetadataArrayLength arrayLengthMode;
GetByIdModeMetadataProtoLoad protoLoadMode;
};
GetByIdMode mode;
static constexpr ptrdiff_t offsetOfMode() { return OBJECT_OFFSETOF(GetByIdModeMetadata, mode); }
uint8_t hitCountForLLIntCaching;
};
#endif
inline void GetByIdModeMetadata::clearToDefaultModeWithoutCache()
{
mode = GetByIdMode::Default;
defaultMode.structureID = StructureID();
defaultMode.cachedOffset = 0;
}
inline void GetByIdModeMetadata::setUnsetMode(Structure* structure)
{
mode = GetByIdMode::Unset;
unsetMode.structureID = structure->id();
defaultMode.cachedOffset = 0;
}
inline void GetByIdModeMetadata::setArrayLengthMode()
{
mode = GetByIdMode::ArrayLength;
// We should clear the structure ID to avoid the old structure ID being saved.
defaultMode.structureID = StructureID();
defaultMode.cachedOffset = 0;
// Prevent the prototype cache from ever happening.
hitCountForLLIntCaching = 0;
}
inline void GetByIdModeMetadata::setProtoLoadMode(Structure* structure, PropertyOffset offset, JSObject* cachedSlot)
{
#if CPU(LITTLE_ENDIAN) && CPU(ADDRESS64)
// We rely on ProtoLoad being 0, or else the high bits of the pointer would write the wrong mode and hit count
static_assert(!static_cast<std::underlying_type_t<GetByIdMode>>(GetByIdMode::ProtoLoad)); // In 64bit architecture, this field is shared with protoLoadMode.cachedSlot.
#else
mode = GetByIdMode::ProtoLoad;
#endif
protoLoadMode.structureID = structure->id();
protoLoadMode.cachedOffset = offset;
// We know that this pointer will remain valid because it will be cleared by either a watchpoint fire or
// during GC when we clear the LLInt caches.
// The write to cachedSlot also writes the mode, since they overlap in the struct layout. We know that
// the mode ProtoLoad is 0 by the static assertion above.
protoLoadMode.cachedSlot = cachedSlot;
ASSERT(mode == GetByIdMode::ProtoLoad);
ASSERT(!hitCountForLLIntCaching);
ASSERT(protoLoadMode.structureID == structure->id());
ASSERT(protoLoadMode.cachedOffset == offset);
ASSERT(protoLoadMode.cachedSlot == cachedSlot);
}
} // namespace JSC
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