perf(transformer/tagged-template-transform): improve performance

[Dunqing]

Made some improvements based on the suggestions in #15664

[Dunqing]

• perf(transformer/tagged-template-transform): improve performance #15834 👈 (View in Graphite)
• fix(transformer/tagged-template-transform): handle \n escape sequences #15830
• main

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[codspeed-hq]

CodSpeed Performance Report

Merging #15834 will not alter performance

_{Comparing 11-18-perf_transformer_tagged-template-transform_improve_performance (2a720db) with main (7c46a9e)}

Summary

✅ 38 untouched
⏩ 7 skipped¹

Footnotes

1. 7 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

[overlookmotel]

I think to avoid a perf hit in enter_expression, you want it to be:

impl<'a> Traverse<'a, TransformState<'a>> for TaggedTemplateTransform<'a, '_> {
    // `#[inline]` because this is a hot path and most `Expression`s are not `TaggedTemplateExpression`s,
    // so we want this inlined to handle the common case without a function call
    #[inline]
    fn enter_expression(&mut self, expr: &mut Expression<'a>, ctx: &mut TraverseCtx<'a>) {
        if matches!(expr, Expression::TaggedTemplateExpression(_)) {
          self.transform_tagged_template(expr, ctx);
        }
    }
}

The idea is that probably 0.01% of Expressions are TaggedTemplateExpressions, so for the common case all you want in the hot path is "Is this a TaggedTemplateExpression? No it's not. Exit." That's a very small function, so it can be inlined, which means no overhead of a function call on the hot path.

[overlookmotel]

Another possible improvement (though it doesn't really matter because TaggedTemplateExpressions are so rare anyway):

There are 2 loops at start of transform_template_literal:

1. Check if all cooked == raw.
2. Convert each cooked to StringLiteral.

You could merge them into 1 loop by doing the cooked == raw check at same time as transforming cooked to strings.

Also the logic for creating template_arguments could avoid vec_from_iter (slow):

let template_arguments = if needs_raw_array {
    let raws_argument = /* ... */;
    ctx.ast.vec_from_array([cooked_argument, raws_argument])
} else {
    ctx.ast.vec1(cooked_argument)
};