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c24c9067ee
Optimize unnecessary check in Vec::retain The function `vec::Vec::retain` only have two stages: 1. Nothing was deleted. 2. Some elements were deleted. Here is an unnecessary check `if g.deleted_cnt > 0` in the loop, and it's difficult for compiler to optimize it. I split the loop into two stages manully and keep the code clean using const generics. I write a special but common bench case for this optimization. I call retain on vec but keep all elements. Before and after this optimization: ``` test vec::bench_retain_whole_100000 ... bench: 84,803 ns/iter (+/- 17,314) ``` ``` test vec::bench_retain_whole_100000 ... bench: 42,638 ns/iter (+/- 16,910) ``` The result is expected, there are two `if`s before the optimization and one `if` after. |
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| .. | ||
| alloc | ||
| backtrace@cc89bb66f9 | ||
| core | ||
| panic_abort | ||
| panic_unwind | ||
| proc_macro | ||
| profiler_builtins | ||
| rtstartup | ||
| rustc-std-workspace-alloc | ||
| rustc-std-workspace-core | ||
| rustc-std-workspace-std | ||
| std | ||
| stdarch@5fdbc476af | ||
| test | ||
| unwind | ||