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LibJS: Shrink Identifier's environment coordinate cache
This patch does two things: - We now use u32 instead of size_t for the hops and index fields in EnvironmentCoordinate. This means we're limited to an environment nesting level and variable count of 4Gs respectively. - Instead of wrapping it in an Optional, EnvironmentCoordinate now has a custom valid/invalid state using a magic marker value. These two changes reduce the size of Identifier by 16 bytes. :^)
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4 changed files with 16 additions and 10 deletions
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@ -12,10 +12,13 @@
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namespace JS {
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struct EnvironmentCoordinate {
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size_t hops { 0 };
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size_t index { 0 };
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u32 hops { invalid_marker };
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u32 index { invalid_marker };
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static constexpr size_t global_marker = 0xffffffff;
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bool is_valid() const { return hops != invalid_marker && index != invalid_marker; }
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static constexpr u32 global_marker = 0xffffffff;
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static constexpr u32 invalid_marker = 0xfffffffe;
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};
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}
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@ -565,8 +565,11 @@ ThrowCompletionOr<Reference> VM::get_identifier_reference(Environment* environme
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// Note: This is an optimization for looking up the same reference.
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Optional<EnvironmentCoordinate> environment_coordinate;
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if (index.has_value())
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environment_coordinate = EnvironmentCoordinate { .hops = hops, .index = index.value() };
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if (index.has_value()) {
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VERIFY(hops <= NumericLimits<u32>::max());
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VERIFY(index.value() <= NumericLimits<u32>::max());
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environment_coordinate = EnvironmentCoordinate { .hops = static_cast<u32>(hops), .index = static_cast<u32>(index.value()) };
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}
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// 3. If exists is true, then
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if (exists) {
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