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LibJS: Don't evaluate computed MemberExpression LHS twice in assignments

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The following snippet would cause "i" to be incremented twice(!):

    let a = []
    let i = 0
    a[++i] += 0

This patch solves the issue by remembering the base object and property
name for computed MemberExpression LHS in codegen. We the store the
result of the assignment to the same object and property (instead of
computing the LHS again).

3 new passes on test262. :^)
This commit is contained in:
Andreas Kling 2023-10-04 15:22:07 +02:00
parent 2083376618
commit 732b39d120
3 changed files with 42 additions and 15 deletions
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14
Userland/Libraries/LibJS/Bytecode/Generator.h
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@ -74,15 +74,17 @@ public:
op->set_source_record({ m_current_ast_node->start_offset(), m_current_ast_node->end_offset() });
}
CodeGenerationErrorOr<void> emit_load_from_reference(JS::ASTNode const&);
struct ReferenceRegisters {
Register base; // [[Base]]
Optional<Register> referenced_name; // [[ReferencedName]]
Register this_value; // [[ThisValue]]
};
CodeGenerationErrorOr<Optional<ReferenceRegisters>> emit_load_from_reference(JS::ASTNode const&);
CodeGenerationErrorOr<void> emit_store_to_reference(JS::ASTNode const&);
CodeGenerationErrorOr<void> emit_store_to_reference(ReferenceRegisters const&);
CodeGenerationErrorOr<void> emit_delete_reference(JS::ASTNode const&);
struct ReferenceRegisters {
Register base; // [[Base]]
Optional<Bytecode::Register> referenced_name; // [[ReferencedName]]
Register this_value; // [[ThisValue]]
};
CodeGenerationErrorOr<ReferenceRegisters> emit_super_reference(MemberExpression const&);
void emit_set_variable(JS::Identifier const& identifier, Bytecode::Op::SetVariable::InitializationMode initialization_mode = Bytecode::Op::SetVariable::InitializationMode::Set, Bytecode::Op::EnvironmentMode mode = Bytecode::Op::EnvironmentMode::Lexical);