Optimize std::str::Chars::next and std::str::Chars::next_back
#142038
+145
−75
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There are only 0x10FFFF possible codepoints, so we can exhaustively test all of them.
By inlining the helper functions, we can expose some opportunites for CSE. Also convert the series of nested `if` branches to early return, which IMO makes the code clearer. Comparison of assembly before and after for `next_code_point`: https://godbolt.org/z/bqcvaYxz1 Comparison of assembly before and after for `next_code_point_reverse`: https://godbolt.org/z/n9WM7hPxv
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ping @scottmcm ? |
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Before/after for
next: https://godbolt.org/z/bqcvaYxz1Before/after for
next_back: https://godbolt.org/z/MvTeeWKsPstd::sys_common::wtf8::Wtf8CodePointswill also benefit from this, since it uses the samenext_code_pointandnext_code_point_reversefunctions internally.I also added tests for all codepoints in the range
0..=char::MAX(including surrogats that can only appear in WTF-8), so the new implementations have been exhaustively tested