Speedup Build::clone: Use Arc instead of String/PathBuf/OsString

[NobodyXu]

TBF, I'm not sure how much this will help real-world usage.

I submit this PR based on the observation that the APIs of Build accepts &str, &Path and &OsStr, so converting them to an Arc<T> should be as cheap as String/PathBuf/OsString given that build-overrides is compiled without optimization, so the compiler cannot simply omit these heap allocation (and even with optimization enabled -O3, it's hard to do so).

While Arc::drop is indeed due to atomic operations, I think this is mostly going to be ok given that the heap deallocation is likely to be more expensive than that since build-overrides uses platform-default allocator, which is often not the most optimized.

Signed-off-by: Jiahao XU Jiahao_XU@outlook.com

[thomcc]

I'm not sure this is worth the trouble, TBH... How often does it get cloned? I suppose it doesn't hurt much.

[NobodyXu]

I'm not sure this is worth the trouble, TBH... How often does it get cloned? I suppose it doesn't hurt much.

I'm also not sure about this, but the change here shall have minimal performance impact on code that does not use Build::clone, that's why I submit the PR even I'm not sure.

But feel free to close it if you feel like there's too much to review and not much gain.

[thomcc]

The review is easy but it causes churn on other PRs. That's the big downside. That said I suppose it's fine.

[thomcc]

Looks harmless, as mentioned.