Auto merge of #96605 - Urgau:string-retain-codegen, r=thomcc

Improve codegen of String::retain method

This pull-request improve the codegen of the `String::retain` method.

Using `unwrap_unchecked` helps the optimizer to not generate a panicking path that will never be taken for valid UTF-8 like string.

Using `encode_utf8` saves us from an expensive call to `memcpy`, as the optimizer is unable to realize that `ch_len <= 4` and so can generate much better assembly code.

https://rust.godbolt.org/z/z73ohenfc

0 files changed, 0 insertions, 0 deletions