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LibJS: Optimize reading known-to-be-initialized var bindings
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Browse source 
`var` bindings are never in the temporal dead zone (TDZ), and so we
know accessing them will not throw.

We now take advantage of this by having a specialized environment
binding value getter that doesn't check for exceptional cases.

1.08x speedup on JetStream.
This commit is contained in:
Andreas Kling 2025-05-04 01:41:49 +02:00 • committed by Andreas Kling
parent ad7c1e147f
commit bf1b754e91
Notes: github-actions[bot] 2025-05-04 00:32:11 +00:00
8 changed files with 90 additions and 15 deletions
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6
Libraries/LibJS/Bytecode/ASTCodegen.cpp
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@ -482,7 +482,11 @@ Bytecode::CodeGenerationErrorOr<Optional<ScopedOperand>> Identifier::generate_by
if (is_global()) {
generator.emit<Bytecode::Op::GetGlobal>(dst, generator.intern_identifier(m_string), generator.next_global_variable_cache());
} else {
generator.emit<Bytecode::Op::GetBinding>(dst, generator.intern_identifier(m_string));
if (declaration_kind() == DeclarationKind::Var) {
generator.emit<Bytecode::Op::GetInitializedBinding>(dst, generator.intern_identifier(m_string));
} else {
generator.emit<Bytecode::Op::GetBinding>(dst, generator.intern_identifier(m_string));
}
}
return dst;
}