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LibJS: Make Optional<StringTableIndex> use less space

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We can use the index's invalid state to signal an empty optional.
This makes Optional<StringTableIndex> 4 bytes instead of 8,
shrinking every bytecode instruction that uses these.
This commit is contained in:
Andreas Kling 2025-04-05 21:46:37 +02:00 • committed by Andreas Kling
parent f1a54ef281
commit 42cc481091
Notes: github-actions[bot] 2025-04-06 00:06:34 +00:00
3 changed files with 110 additions and 6 deletions
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105
Libraries/LibJS/Bytecode/StringTable.h
View file

@ -12,7 +12,11 @@
namespace JS::Bytecode {
AK_TYPEDEF_DISTINCT_NUMERIC_GENERAL(u32, StringTableIndex, Comparison);
struct StringTableIndex {
static constexpr u32 invalid = 0xffffffffu;
bool is_valid() const { return value != invalid; }
u32 value { 0 };
};
class StringTable {
AK_MAKE_NONMOVABLE(StringTable);
@ -31,3 +35,102 @@ private:
};
}
namespace AK {
template<>
class Optional<JS::Bytecode::StringTableIndex> : public OptionalBase<JS::Bytecode::StringTableIndex> {
template<typename U>
friend class Optional;
public:
using ValueType = JS::Bytecode::StringTableIndex;
Optional() = default;
template<SameAs<OptionalNone> V>
Optional(V) { }
Optional(Optional<JS::Bytecode::StringTableIndex> const& other)
{
if (other.has_value())
m_value = other.m_value;
}
Optional(Optional&& other)
: m_value(other.m_value)
{
}
template<typename U = JS::Bytecode::StringTableIndex>
requires(!IsSame<OptionalNone, RemoveCVReference<U>>)
explicit(!IsConvertible<U&&, JS::Bytecode::StringTableIndex>) Optional(U&& value)
requires(!IsSame<RemoveCVReference<U>, Optional<JS::Bytecode::StringTableIndex>> && IsConstructible<JS::Bytecode::StringTableIndex, U &&>)
: m_value(forward<U>(value))
{
}
template<SameAs<OptionalNone> V>
Optional& operator=(V)
{
clear();
return *this;
}
Optional& operator=(Optional const& other)
{
if (this != &other) {
clear();
m_value = other.m_value;
}
return *this;
}
Optional& operator=(Optional&& other)
{
if (this != &other) {
clear();
m_value = other.m_value;
}
return *this;
}
void clear()
{
m_value.value = JS::Bytecode::StringTableIndex::invalid;
}
[[nodiscard]] bool has_value() const
{
return m_value.is_valid();
}
[[nodiscard]] JS::Bytecode::StringTableIndex& value() &
{
VERIFY(has_value());
return m_value;
}
[[nodiscard]] JS::Bytecode::StringTableIndex const& value() const&
{
VERIFY(has_value());
return m_value;
}
[[nodiscard]] JS::Bytecode::StringTableIndex value() &&
{
return release_value();
}
[[nodiscard]] JS::Bytecode::StringTableIndex release_value()
{
VERIFY(has_value());
JS::Bytecode::StringTableIndex released_value = m_value;
clear();
return released_value;
}
private:
JS::Bytecode::StringTableIndex m_value { JS::Bytecode::StringTableIndex::invalid };
};
}