Add is_ascii function optimized for LoongArch64 for [u8] #146699
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Similar to x86_64, on LoongArch64 we use the `vmskltz.b` instruction to test the high bit in a lane. For longer input cases, the performance improvement is significant. For unaligned cases close to 32 bytes in length, there's some regression, but it seems acceptable. | core benches (MB/s) | Before | After | % | |--------------------------------------------------------|--------|--------|---------| | ascii::is_ascii::short::case00_libcore | 1000 | 1000 | 0.00 | | ascii::is_ascii::medium::case00_libcore | 8000 | 8000 | 0.00 | | ascii::is_ascii::long::case00_libcore | 183947 | 436875 | +137.50 | | ascii::is_ascii::unaligned_head_medium::case00_libcore | 7750 | 2818 | -63.64 | | ascii::is_ascii::unaligned_head_long::case00_libcore | 317681 | 436812 | +37.50 | | ascii::is_ascii::unaligned_tail_medium::case00_libcore | 7750 | 3444 | -55.56 | | ascii::is_ascii::unaligned_tail_long::case00_libcore | 155311 | 436812 | +181.25 | | ascii::is_ascii::unaligned_both_medium::case00_libcore | 7500 | 3333 | -55.56 | | ascii::is_ascii::unaligned_both_long::case00_libcore | 174700 | 436750 | +150.00 |
rustbot added S-waiting-on-review 
| r? libs |
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Similar to x86_64, on LoongArch64 we use the
vmskltz.binstruction to test the high bit in a lane.For longer input cases, the performance improvement is significant. For unaligned cases close to 32 bytes in length, there's some regression, but it seems acceptable.