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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
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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17
Libraries/LibJS/AST.h
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@ -159,6 +159,13 @@ private:
u32 m_tail_size { 0 };
};
enum class DeclarationKind {
None,
Var,
Let,
Const,
};
class Statement : public ASTNode {
public:
explicit Statement(SourceRange source_range)
@ -702,6 +709,9 @@ public:
bool is_global() const { return m_is_global; }
void set_is_global() { m_is_global = true; }
[[nodiscard]] DeclarationKind declaration_kind() const { return m_declaration_kind; }
void set_declaration_kind(DeclarationKind kind) { m_declaration_kind = kind; }
virtual void dump(int indent) const override;
virtual Bytecode::CodeGenerationErrorOr<Optional<Bytecode::ScopedOperand>> generate_bytecode(Bytecode::Generator&, Optional<Bytecode::ScopedOperand> preferred_dst = {}) const override;
@ -712,6 +722,7 @@ private:
Optional<Local> m_local_index;
bool m_is_global { false };
DeclarationKind m_declaration_kind { DeclarationKind::None };
};
struct FunctionParameter {
@ -1764,12 +1775,6 @@ private:
bool m_prefixed;
};
enum class DeclarationKind {
Var,
Let,
Const,
};
class VariableDeclarator final : public ASTNode {
public:
VariableDeclarator(SourceRange source_range, NonnullRefPtr<Identifier const> id)