Safety:
For a function-local variable, an expression with side-effects would be a call, including an indirect one with a member expression.
- If the call is function-local, it will be analyzed by the analyzer and inliner will not work.
- If the call is not a function-local one, it cannot modify the local variable.
- We don't need a list of bindings to check if an identifier is unresolved.
- Checking if an identifier is unresolved is now one CPU instruction.
- Previously it was one hashmap operation.
- This PR also improves performance, by removing the hashmaps mentioned above.
swc_ecma_minifier:
- `pure`: Add an optional list of bindings.
- `pure`: Drop identifier only if we have the complete list of bindings.
- `pure`: Allow using `GLOBALS`.
- `pure`: Drop some pure member expressions.
- Move identifier dropping logic from the stateful optimizer to the pure optimizer.
- `pure`: Drop more references to global declarations.
swc_ecma_transforms_optimization:
- `expr_simplifier`: Track more changes.
swc_ecma_minifier:
- Analyze after applying the pure optimizer.
- Preserve access to a variable not in scope.
- `compress`: Remove string literal if it was not a directive.
- `pure/collapse_vars`: Merge vars declared in the first statement into one with initializers if `collapse_vars` and `join_vars` are enabled.
- `unused`: Use `usage_count` instead of `ref_count`.
- `unused`: Fix dropping rule for member expressions.
- `unused`: Fix dropping rule for declarations.
- `hoist_props`: Preserve exported items.
