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-rw-r--r--js/public/Value.h55
1 files changed, 51 insertions, 4 deletions
diff --git a/js/public/Value.h b/js/public/Value.h
index a40e65c83..01666ed4e 100644
--- a/js/public/Value.h
+++ b/js/public/Value.h
@@ -140,12 +140,16 @@ static_assert(sizeof(JSValueShiftedTag) == sizeof(uint64_t),
#define JSVAL_TYPE_TO_TAG(type) ((JSValueTag)(JSVAL_TAG_CLEAR | (type)))
+#define JSVAL_RAW64_UNDEFINED (uint64_t(JSVAL_TAG_UNDEFINED) << 32)
+
#define JSVAL_UPPER_EXCL_TAG_OF_PRIMITIVE_SET JSVAL_TAG_OBJECT
#define JSVAL_UPPER_INCL_TAG_OF_NUMBER_SET JSVAL_TAG_INT32
#define JSVAL_LOWER_INCL_TAG_OF_GCTHING_SET JSVAL_TAG_STRING
#elif defined(JS_PUNBOX64)
+#define JSVAL_RAW64_UNDEFINED (uint64_t(JSVAL_TAG_UNDEFINED) << JSVAL_TAG_SHIFT)
+
#define JSVAL_PAYLOAD_MASK 0x00007FFFFFFFFFFFLL
#define JSVAL_TAG_MASK 0xFFFF800000000000LL
#define JSVAL_TYPE_TO_TAG(type) ((JSValueTag)(JSVAL_TAG_MAX_DOUBLE | (type)))
@@ -817,7 +821,7 @@ class MOZ_NON_PARAM alignas(8) Value
double asDouble;
void* asPtr;
- layout() = default;
+ layout() : asBits(JSVAL_RAW64_UNDEFINED) {}
explicit constexpr layout(uint64_t bits) : asBits(bits) {}
explicit constexpr layout(double d) : asDouble(d) {}
} data;
@@ -843,7 +847,7 @@ class MOZ_NON_PARAM alignas(8) Value
size_t asWord;
uintptr_t asUIntPtr;
- layout() = default;
+ layout() : asBits(JSVAL_RAW64_UNDEFINED) {}
explicit constexpr layout(uint64_t bits) : asBits(bits) {}
explicit constexpr layout(double d) : asDouble(d) {}
} data;
@@ -871,7 +875,7 @@ class MOZ_NON_PARAM alignas(8) Value
double asDouble;
void* asPtr;
- layout() = default;
+ layout() : asBits(JSVAL_RAW64_UNDEFINED) {}
explicit constexpr layout(uint64_t bits) : asBits(bits) {}
explicit constexpr layout(double d) : asDouble(d) {}
} data;
@@ -895,7 +899,7 @@ class MOZ_NON_PARAM alignas(8) Value
size_t asWord;
uintptr_t asUIntPtr;
- layout() = default;
+ layout() : asBits(JSVAL_RAW64_UNDEFINED) {}
explicit constexpr layout(uint64_t bits) : asBits(bits) {}
explicit constexpr layout(double d) : asDouble(d) {}
} data;
@@ -948,8 +952,51 @@ class MOZ_NON_PARAM alignas(8) Value
}
} JS_HAZ_GC_POINTER;
+/**
+ * This is a null-constructible structure that can convert to and from
+ * a Value, allowing UninitializedValue to be stored in unions.
+ */
+struct MOZ_NON_PARAM alignas(8) UninitializedValue
+{
+ private:
+ uint64_t bits;
+
+ public:
+ UninitializedValue() = default;
+ UninitializedValue(const UninitializedValue&) = default;
+ MOZ_IMPLICIT UninitializedValue(const Value& val) : bits(val.asRawBits()) {}
+
+ inline uint64_t asRawBits() const {
+ return bits;
+ }
+
+ inline Value& asValueRef() {
+ return *reinterpret_cast<Value*>(this);
+ }
+ inline const Value& asValueRef() const {
+ return *reinterpret_cast<const Value*>(this);
+ }
+
+ inline operator Value&() {
+ return asValueRef();
+ }
+ inline operator Value const&() const {
+ return asValueRef();
+ }
+ inline operator Value() const {
+ return asValueRef();
+ }
+
+ inline void operator=(Value const& other) {
+ asValueRef() = other;
+ }
+};
+
static_assert(sizeof(Value) == 8, "Value size must leave three tag bits, be a binary power, and is ubiquitously depended upon everywhere");
+static_assert(sizeof(UninitializedValue) == sizeof(Value), "Value and UninitializedValue must be the same size");
+static_assert(alignof(UninitializedValue) == alignof(Value), "Value and UninitializedValue must have same alignment");
+
inline bool
IsOptimizedPlaceholderMagicValue(const Value& v)
{