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LibJS: Shrink Identifier's environment coordinate cache

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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. :^)
This commit is contained in:
Andreas Kling 2022-11-21 18:01:22 +01:00
parent 76f438eb3e
commit 0f1f925532
4 changed files with 16 additions and 10 deletions
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7
Userland/Libraries/LibJS/Runtime/VM.cpp
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@ -565,8 +565,11 @@ ThrowCompletionOr<Reference> VM::get_identifier_reference(Environment* environme
// Note: This is an optimization for looking up the same reference.
Optional<EnvironmentCoordinate> environment_coordinate;
if (index.has_value())
environment_coordinate = EnvironmentCoordinate { .hops = hops, .index = index.value() };
if (index.has_value()) {
VERIFY(hops <= NumericLimits<u32>::max());
VERIFY(index.value() <= NumericLimits<u32>::max());
environment_coordinate = EnvironmentCoordinate { .hops = static_cast<u32>(hops), .index = static_cast<u32>(index.value()) };
}
// 3. If exists is true, then
if (exists) {