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Diffstat (limited to 'src/qml/common/qv4staticvalue_p.h')
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diff --git a/src/qml/common/qv4staticvalue_p.h b/src/qml/common/qv4staticvalue_p.h new file mode 100644 index 0000000000..9b4f582c00 --- /dev/null +++ b/src/qml/common/qv4staticvalue_p.h @@ -0,0 +1,683 @@ +// Copyright (C) 2019 The Qt Company Ltd. +// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR LGPL-3.0-only OR GPL-2.0-only OR GPL-3.0-only +#ifndef QV4STATICVALUE_P_H +#define QV4STATICVALUE_P_H + +// +// W A R N I N G +// ------------- +// +// This file is not part of the Qt API. It exists purely as an +// implementation detail. This header file may change from version to +// version without notice, or even be removed. +// +// We mean it. +// + +#include <qjsnumbercoercion.h> + +#include <QtCore/private/qnumeric_p.h> +#include <private/qtqmlglobal_p.h> + +#include <cstring> + +#ifdef QT_NO_DEBUG +#define QV4_NEARLY_ALWAYS_INLINE Q_ALWAYS_INLINE +#else +#define QV4_NEARLY_ALWAYS_INLINE inline +#endif + +QT_BEGIN_NAMESPACE + +namespace QV4 { + +// ReturnedValue is used to return values from runtime methods +// the type has to be a primitive type (no struct or union), so that the compiler +// will return it in a register on all platforms. +// It will be returned in rax on x64, [eax,edx] on x86 and [r0,r1] on arm +typedef quint64 ReturnedValue; + +namespace Heap { +struct Base; +} + +struct StaticValue +{ + using HeapBasePtr = Heap::Base *; + + StaticValue() = default; + constexpr StaticValue(quint64 val) : _val(val) {} + + StaticValue &operator=(ReturnedValue v) + { + _val = v; + return *this; + } + + template<typename Value> + StaticValue &operator=(const Value &); + + template<typename Value> + const Value &asValue() const; + + template<typename Value> + Value &asValue(); + + /* + We use 8 bytes for a value. In order to store all possible values we employ a variant of NaN + boxing. A "special" Double is indicated by a number that has the 11 exponent bits set to 1. + Those can be NaN, positive or negative infinity. We only store one variant of NaN: The sign + bit has to be off and the bit after the exponent ("quiet bit") has to be on. However, since + the exponent bits are enough to identify special doubles, we can use a different bit as + discriminator to tell us how the rest of the bits (including quiet and sign) are to be + interpreted. This bit is bit 48. If set, we have an unmanaged value, which includes the + special doubles and various other values. If unset, we have a managed value, and all of the + other bits can be used to assemble a pointer. + + On 32bit systems the pointer can just live in the lower 4 bytes. On 64 bit systems the lower + 48 bits can be used for verbatim pointer bits. However, since all our heap objects are + aligned to 32 bytes, we can use the 5 least significant bits of the pointer to store, e.g. + pointer tags on android. The same holds for the 3 bits between the double exponent and + bit 48. + + With that out of the way, we can use the other bits to store different values. + + We xor Doubles with (0x7ff48000 << 32). That has the effect that any double with all the + exponent bits set to 0 is one of our special doubles. Those special doubles then get the + other two bits in the mask (Special and Number) set to 1, as they cannot have 1s in those + positions to begin with. + + We dedicate further bits to integer-convertible and bool-or-int. With those bits we can + describe all values we need to store. + + Undefined is encoded as a managed pointer with value 0. This is the same as a nullptr. + + Specific bit-sequences: + 0 = always 0 + 1 = always 1 + x = stored value + y = stored value, shifted to different position + a = xor-ed bits, where at least one bit is set + b = xor-ed bits + + 32109876 54321098 76543210 98765432 10987654 32109876 54321098 76543210 | + 66665555 55555544 44444444 33333333 33222222 22221111 11111100 00000000 | JS Value + ------------------------------------------------------------------------+-------------- + 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 | Undefined + y0000000 0000yyy0 xxxxxxxx xxxxxxxx xxxxxxxx xxxxxxxx xxxxxxxx xxxyyyyy | Managed (heap pointer) + 00000000 00001101 10000000 00000000 00000000 00000000 00000000 00000000 | NaN + 00000000 00000101 10000000 00000000 00000000 00000000 00000000 00000000 | +Inf + 10000000 00000101 10000000 00000000 00000000 00000000 00000000 00000000 | -Inf + xaaaaaaa aaaaxbxb bxxxxxxx xxxxxxxx xxxxxxxx xxxxxxxx xxxxxxxx xxxxxxxx | double + 00000000 00000001 00000000 00000000 00000000 00000000 00000000 00000000 | empty (non-sparse array hole) + 00000000 00000011 00000000 00000000 00000000 00000000 00000000 00000000 | Null + 00000000 00000011 10000000 00000000 00000000 00000000 00000000 0000000x | Bool + 00000000 00000011 11000000 00000000 xxxxxxxx xxxxxxxx xxxxxxxx xxxxxxxx | Int + ^ ^^^ ^^ + | ||| || + | ||| |+-> Number + | ||| +--> Int or Bool + | ||+----> Unmanaged + | |+-----> Integer compatible + | +------> Special double + +--------------------> Double sign, also used for special doubles + */ + + quint64 _val; + + QV4_NEARLY_ALWAYS_INLINE constexpr quint64 &rawValueRef() { return _val; } + QV4_NEARLY_ALWAYS_INLINE constexpr quint64 rawValue() const { return _val; } + QV4_NEARLY_ALWAYS_INLINE constexpr void setRawValue(quint64 raw) { _val = raw; } + +#if Q_BYTE_ORDER == Q_LITTLE_ENDIAN + static inline int valueOffset() { return 0; } + static inline int tagOffset() { return 4; } +#else // !Q_LITTLE_ENDIAN + static inline int valueOffset() { return 4; } + static inline int tagOffset() { return 0; } +#endif + static inline constexpr quint64 tagValue(quint32 tag, quint32 value) { return quint64(tag) << Tag_Shift | value; } + QV4_NEARLY_ALWAYS_INLINE constexpr void setTagValue(quint32 tag, quint32 value) { _val = quint64(tag) << Tag_Shift | value; } + QV4_NEARLY_ALWAYS_INLINE constexpr quint32 value() const { return _val & quint64(~quint32(0)); } + QV4_NEARLY_ALWAYS_INLINE constexpr quint32 tag() const { return _val >> Tag_Shift; } + QV4_NEARLY_ALWAYS_INLINE constexpr void setTag(quint32 tag) { setTagValue(tag, value()); } + + QV4_NEARLY_ALWAYS_INLINE constexpr int int_32() const + { + return int(value()); + } + QV4_NEARLY_ALWAYS_INLINE constexpr void setInt_32(int i) + { + setTagValue(quint32(QuickType::Integer), quint32(i)); + } + QV4_NEARLY_ALWAYS_INLINE uint uint_32() const { return value(); } + + QV4_NEARLY_ALWAYS_INLINE constexpr void setEmpty() + { + setTagValue(quint32(QuickType::Empty), 0); + } + + enum class TagBit { + // s: sign bit + // e: double exponent bit + // u: upper 3 bits if managed + // m: bit 48, denotes "unmanaged" if 1 + // p: significant pointer bits (some re-used for non-managed) + // seeeeeeeeeeeuuumpppp + SpecialNegative = 0b10000000000000000000 << 12, + SpecialQNaN = 0b00000000000010000000 << 12, + Special = 0b00000000000001000000 << 12, + IntCompat = 0b00000000000000100000 << 12, + Unmanaged = 0b00000000000000010000 << 12, + IntOrBool = 0b00000000000000001000 << 12, + Number = 0b00000000000000000100 << 12, + }; + + static inline constexpr quint64 tagBitMask(TagBit bit) { return quint64(bit) << Tag_Shift; } + + enum Type { + // Managed, Double and undefined are not directly encoded + Managed_Type = 0, + Double_Type = 1, + Undefined_Type = 2, + + Empty_Type = quint32(TagBit::Unmanaged), + Null_Type = Empty_Type | quint32(TagBit::IntCompat), + Boolean_Type = Null_Type | quint32(TagBit::IntOrBool), + Integer_Type = Boolean_Type | quint32(TagBit::Number) + }; + + enum { + Tag_Shift = 32, + + IsIntegerConvertible_Shift = 48, + IsIntegerConvertible_Value = 3, // Unmanaged | IntCompat after shifting + + IsIntegerOrBool_Shift = 47, + IsIntegerOrBool_Value = 7, // Unmanaged | IntCompat | IntOrBool after shifting + }; + + static_assert(IsIntegerConvertible_Value == + (quint32(TagBit::IntCompat) | quint32(TagBit::Unmanaged)) + >> (IsIntegerConvertible_Shift - Tag_Shift)); + + static_assert(IsIntegerOrBool_Value == + (quint32(TagBit::IntOrBool) | quint32(TagBit::IntCompat) | quint32(TagBit::Unmanaged)) + >> (IsIntegerOrBool_Shift - Tag_Shift)); + + static constexpr quint64 ExponentMask = 0b0111111111110000ull << 48; + + static constexpr quint64 Top1Mask = 0b1000000000000000ull << 48; + static constexpr quint64 Upper3Mask = 0b0000000000001110ull << 48; + static constexpr quint64 Lower5Mask = 0b0000000000011111ull; + + static constexpr quint64 ManagedMask = ExponentMask | quint64(TagBit::Unmanaged) << Tag_Shift; + static constexpr quint64 DoubleMask = ManagedMask | quint64(TagBit::Special) << Tag_Shift; + static constexpr quint64 NumberMask = ManagedMask | quint64(TagBit::Number) << Tag_Shift; + static constexpr quint64 IntOrBoolMask = ManagedMask | quint64(TagBit::IntOrBool) << Tag_Shift; + static constexpr quint64 IntCompatMask = ManagedMask | quint64(TagBit::IntCompat) << Tag_Shift; + + static constexpr quint64 EncodeMask = DoubleMask | NumberMask; + + static constexpr quint64 DoubleDiscriminator + = ((quint64(TagBit::Unmanaged) | quint64(TagBit::Special)) << Tag_Shift); + static constexpr quint64 NumberDiscriminator + = ((quint64(TagBit::Unmanaged) | quint64(TagBit::Number)) << Tag_Shift); + + // Things we can immediately determine by just looking at the upper 4 bytes. + enum class QuickType : quint32 { + // Managed takes precedence over all others. That is, other bits may be set if it's managed. + // However, since all others include the Unmanaged bit, we can still check them with simple + // equality operations. + Managed = Managed_Type, + + Empty = Empty_Type, + Null = Null_Type, + Boolean = Boolean_Type, + Integer = Integer_Type, + + PlusInf = quint32(TagBit::Number) | quint32(TagBit::Special) | quint32(TagBit::Unmanaged), + MinusInf = PlusInf | quint32(TagBit::SpecialNegative), + NaN = PlusInf | quint32(TagBit::SpecialQNaN), + MinusNaN = NaN | quint32(TagBit::SpecialNegative), // Can happen with UMinus on NaN + // All other values are doubles + }; + + // Aliases for easier porting. Remove those when possible + using ValueTypeInternal = QuickType; + enum { + QT_Empty = Empty_Type, + QT_Null = Null_Type, + QT_Bool = Boolean_Type, + QT_Int = Integer_Type, + QuickType_Shift = Tag_Shift, + }; + + inline Type type() const + { + const quint64 masked = _val & DoubleMask; + if (masked >= DoubleDiscriminator) + return Double_Type; + + // Any bit set in the exponent would have been caught above, as well as both bits being set. + // None of them being set as well as only Special being set means "managed". + // Only Unmanaged being set means "unmanaged". That's all remaining options. + if (masked != tagBitMask(TagBit::Unmanaged)) { + Q_ASSERT((_val & tagBitMask(TagBit::Unmanaged)) == 0); + return isUndefined() ? Undefined_Type : Managed_Type; + } + + const Type ret = Type(tag()); + Q_ASSERT( + ret == Empty_Type || + ret == Null_Type || + ret == Boolean_Type || + ret == Integer_Type); + return ret; + } + + inline quint64 quickType() const { return (_val >> QuickType_Shift); } + + // used internally in property + inline bool isEmpty() const { return tag() == quint32(ValueTypeInternal::Empty); } + inline bool isNull() const { return tag() == quint32(ValueTypeInternal::Null); } + inline bool isBoolean() const { return tag() == quint32(ValueTypeInternal::Boolean); } + inline bool isInteger() const { return tag() == quint32(ValueTypeInternal::Integer); } + inline bool isNullOrUndefined() const { return isNull() || isUndefined(); } + inline bool isUndefined() const { return _val == 0; } + + inline bool isDouble() const + { + // If any of the flipped exponent bits are 1, it's a regular double, and the masked tag is + // larger than Unmanaged | Special. + // + // If all (flipped) exponent bits are 0: + // 1. If Unmanaged bit is 0, it's managed + // 2. If the Unmanaged bit it is 1, and the Special bit is 0, it's not a special double + // 3. If both are 1, it is a special double and the masked tag equals Unmanaged | Special. + + return (_val & DoubleMask) >= DoubleDiscriminator; + } + + inline bool isNumber() const + { + // If any of the flipped exponent bits are 1, it's a regular double, and the masked tag is + // larger than Unmanaged | Number. + // + // If all (flipped) exponent bits are 0: + // 1. If Unmanaged bit is 0, it's managed + // 2. If the Unmanaged bit it is 1, and the Number bit is 0, it's not number + // 3. If both are 1, it is a number and masked tag equals Unmanaged | Number. + + return (_val & NumberMask) >= NumberDiscriminator; + } + + inline bool isManagedOrUndefined() const { return (_val & ManagedMask) == 0; } + + // If any other bit is set in addition to the managed mask, it's not undefined. + inline bool isManaged() const + { + return isManagedOrUndefined() && !isUndefined(); + } + + inline bool isIntOrBool() const + { + // It's an int or bool if all the exponent bits are 0, + // and the "int or bool" bit as well as the "umanaged" bit are set, + return (_val >> IsIntegerOrBool_Shift) == IsIntegerOrBool_Value; + } + + inline bool integerCompatible() const { + Q_ASSERT(!isEmpty()); + return (_val >> IsIntegerConvertible_Shift) == IsIntegerConvertible_Value; + } + + static inline bool integerCompatible(StaticValue a, StaticValue b) { + return a.integerCompatible() && b.integerCompatible(); + } + + static inline bool bothDouble(StaticValue a, StaticValue b) { + return a.isDouble() && b.isDouble(); + } + + inline bool isNaN() const + { + switch (QuickType(tag())) { + case QuickType::NaN: + case QuickType::MinusNaN: + return true; + default: + return false; + } + } + + inline bool isPositiveInt() const { + return isInteger() && int_32() >= 0; + } + + QV4_NEARLY_ALWAYS_INLINE double doubleValue() const { + Q_ASSERT(isDouble()); + double d; + const quint64 unmasked = _val ^ EncodeMask; + memcpy(&d, &unmasked, 8); + return d; + } + + QV4_NEARLY_ALWAYS_INLINE void setDouble(double d) { + if (qt_is_nan(d)) { + // We cannot store just any NaN. It has to be a NaN with only the quiet bit + // set in the upper bits of the mantissa and the sign bit either on or off. + // qt_qnan() happens to produce such a thing via std::numeric_limits, + // but this is actually not guaranteed. Therefore, we make our own. + _val = (quint64(std::signbit(d) ? QuickType::MinusNaN : QuickType::NaN) << Tag_Shift); + Q_ASSERT(isNaN()); + } else { + memcpy(&_val, &d, 8); + _val ^= EncodeMask; + } + + Q_ASSERT(isDouble()); + } + + inline bool isInt32() { + if (tag() == quint32(QuickType::Integer)) + return true; + if (isDouble()) { + double d = doubleValue(); + if (isInt32(d)) { + setInt_32(int(d)); + return true; + } + } + return false; + } + + QV4_NEARLY_ALWAYS_INLINE static bool isInt32(double d) { + int i = QJSNumberCoercion::toInteger(d); + return (i == d && !(d == 0 && std::signbit(d))); + } + + double asDouble() const { + if (tag() == quint32(QuickType::Integer)) + return int_32(); + return doubleValue(); + } + + bool booleanValue() const { + return int_32(); + } + + int integerValue() const { + return int_32(); + } + + inline bool tryIntegerConversion() { + bool b = integerCompatible(); + if (b) + setTagValue(quint32(QuickType::Integer), value()); + return b; + } + + bool toBoolean() const { + if (integerCompatible()) + return static_cast<bool>(int_32()); + + if (isManagedOrUndefined()) + return false; + + // double + const double d = doubleValue(); + return d && !std::isnan(d); + } + + inline int toInt32() const + { + switch (type()) { + case Null_Type: + case Boolean_Type: + case Integer_Type: + return int_32(); + case Double_Type: + return QJSNumberCoercion::toInteger(doubleValue()); + case Empty_Type: + case Undefined_Type: + case Managed_Type: + return 0; // Coercion of NaN to int, results in 0; + } + + Q_UNREACHABLE_RETURN(0); + } + + ReturnedValue *data_ptr() { return &_val; } + constexpr ReturnedValue asReturnedValue() const { return _val; } + constexpr static StaticValue fromReturnedValue(ReturnedValue val) { return {val}; } + + inline static constexpr StaticValue emptyValue() { return { tagValue(quint32(QuickType::Empty), 0) }; } + static inline constexpr StaticValue fromBoolean(bool b) { return { tagValue(quint32(QuickType::Boolean), b) }; } + static inline constexpr StaticValue fromInt32(int i) { return { tagValue(quint32(QuickType::Integer), quint32(i)) }; } + inline static constexpr StaticValue undefinedValue() { return { 0 }; } + static inline constexpr StaticValue nullValue() { return { tagValue(quint32(QuickType::Null), 0) }; } + + static inline StaticValue fromDouble(double d) + { + StaticValue v; + v.setDouble(d); + return v; + } + + static inline StaticValue fromUInt32(uint i) + { + StaticValue v; + if (i < uint(std::numeric_limits<int>::max())) { + v.setTagValue(quint32(QuickType::Integer), i); + } else { + v.setDouble(i); + } + return v; + } + + static double toInteger(double d) + { + if (std::isnan(d)) + return +0; + if (!d || std::isinf(d)) + return d; + return d >= 0 ? std::floor(d) : std::ceil(d); + } + + static int toInt32(double d) + { + return QJSNumberCoercion::toInteger(d); + } + + static unsigned int toUInt32(double d) + { + return static_cast<uint>(toInt32(d)); + } + + // While a value containing a Heap::Base* is not actually static, we still implement + // the setting and retrieving of heap pointers here in order to have the encoding + // scheme completely in one place. + +#if QT_POINTER_SIZE == 8 + + // All pointer shifts are from more significant to less significant bits. + // When encoding, we shift right by that amount. When decoding, we shift left. + // Negative numbers mean shifting the other direction. 0 means no shifting. + // + // The IA64 and Sparc64 cases are mostly there to demonstrate the idea. Sparc64 + // and IA64 are not officially supported, but we can expect more platforms with + // similar "problems" in the future. + enum PointerShift { +#if 0 && defined(Q_OS_ANDROID) && defined(Q_PROCESSOR_ARM_64) + // We used to assume that Android on arm64 uses the top byte to store pointer tags. + // However, at least currently, the pointer tags are only applied on new/malloc and + // delete/free, not on mmap() and munmap(). We manage the JS heap directly using + // mmap, so we don't have to preserve any tags. + // + // If this ever changes, here is how to preserve the top byte: + // Move it to Upper3 and Lower5. + Top1Shift = 0, + Upper3Shift = 12, + Lower5Shift = 56, +#elif defined(Q_PROCESSOR_IA64) + // On ia64, bits 63-61 in a 64-bit pointer are used to store the virtual region + // number. We can move those to Upper3. + Top1Shift = 0, + Upper3Shift = 12, + Lower5Shift = 0, +#elif defined(Q_PROCESSOR_SPARC_64) + // Sparc64 wants to use 52 bits for pointers. + // Upper3 can stay where it is, bit48 moves to the top bit. + Top1Shift = -15, + Upper3Shift = 0, + Lower5Shift = 0, +#elif 0 // TODO: Once we need 5-level page tables, add the appropriate check here. + // With 5-level page tables (as possible on linux) we need 57 address bits. + // Upper3 can stay where it is, bit48 moves to the top bit, the rest moves to Lower5. + Top1Shift = -15, + Upper3Shift = 0, + Lower5Shift = 52, +#else + Top1Shift = 0, + Upper3Shift = 0, + Lower5Shift = 0 +#endif + }; + + template<int Offset, quint64 Mask> + static constexpr quint64 movePointerBits(quint64 val) + { + if constexpr (Offset > 0) + return (val & ~Mask) | ((val & Mask) >> Offset); + if constexpr (Offset < 0) + return (val & ~Mask) | ((val & Mask) << -Offset); + return val; + } + + template<int Offset, quint64 Mask> + static constexpr quint64 storePointerBits(quint64 val) + { + constexpr quint64 OriginMask = movePointerBits<-Offset, Mask>(Mask); + return movePointerBits<Offset, OriginMask>(val); + } + + template<int Offset, quint64 Mask> + static constexpr quint64 retrievePointerBits(quint64 val) + { + return movePointerBits<-Offset, Mask>(val); + } + + QML_NEARLY_ALWAYS_INLINE HeapBasePtr m() const + { + Q_ASSERT(!(_val & ManagedMask)); + + // Re-assemble the pointer from its fragments. + const quint64 tmp = retrievePointerBits<Top1Shift, Top1Mask>( + retrievePointerBits<Upper3Shift, Upper3Mask>( + retrievePointerBits<Lower5Shift, Lower5Mask>(_val))); + + HeapBasePtr b; + memcpy(&b, &tmp, 8); + return b; + } + QML_NEARLY_ALWAYS_INLINE void setM(HeapBasePtr b) + { + quint64 tmp; + memcpy(&tmp, &b, 8); + + // Has to be aligned to 32 bytes + Q_ASSERT(!(tmp & Lower5Mask)); + + // MinGW produces a bogus warning about array bounds. + // There is no array access here. + QT_WARNING_PUSH + QT_WARNING_DISABLE_GCC("-Warray-bounds") + + // Encode the pointer. + _val = storePointerBits<Top1Shift, Top1Mask>( + storePointerBits<Upper3Shift, Upper3Mask>( + storePointerBits<Lower5Shift, Lower5Mask>(tmp))); + + QT_WARNING_POP + } +#elif QT_POINTER_SIZE == 4 + QML_NEARLY_ALWAYS_INLINE HeapBasePtr m() const + { + Q_STATIC_ASSERT(sizeof(HeapBasePtr) == sizeof(quint32)); + HeapBasePtr b; + quint32 v = value(); + memcpy(&b, &v, 4); + return b; + } + QML_NEARLY_ALWAYS_INLINE void setM(HeapBasePtr b) + { + quint32 v; + memcpy(&v, &b, 4); + setTagValue(quint32(QuickType::Managed), v); + } +#else +# error "unsupported pointer size" +#endif +}; +Q_STATIC_ASSERT(std::is_trivial_v<StaticValue>); + +struct Encode { + static constexpr ReturnedValue undefined() { + return StaticValue::undefinedValue().asReturnedValue(); + } + static constexpr ReturnedValue null() { + return StaticValue::nullValue().asReturnedValue(); + } + + explicit constexpr Encode(bool b) + : val(StaticValue::fromBoolean(b).asReturnedValue()) + { + } + explicit Encode(double d) { + val = StaticValue::fromDouble(d).asReturnedValue(); + } + explicit constexpr Encode(int i) + : val(StaticValue::fromInt32(i).asReturnedValue()) + { + } + explicit Encode(uint i) { + val = StaticValue::fromUInt32(i).asReturnedValue(); + } + explicit constexpr Encode(ReturnedValue v) + : val(v) + { + } + constexpr Encode(StaticValue v) + : val(v.asReturnedValue()) + { + } + + template<typename HeapBase> + explicit Encode(HeapBase *o); + + explicit Encode(StaticValue *o) { + Q_ASSERT(o); + val = o->asReturnedValue(); + } + + static ReturnedValue smallestNumber(double d) { + if (StaticValue::isInt32(d)) + return Encode(static_cast<int>(d)); + else + return Encode(d); + } + + constexpr operator ReturnedValue() const { + return val; + } + quint64 val; +private: + explicit Encode(void *); +}; + +} + +QT_END_NAMESPACE + +#endif // QV4STATICVALUE_P_H |