From: Ralf Jung Date: Tue, 29 Sep 2020 07:49:50 +0000 (+0200) Subject: better wording X-Git-Url: https://git.ralfj.de/web.git/commitdiff_plain/ec451ba49f3dd7cb3b9afd890f381d63308be40a?ds=inline;hp=5c18998b2223a8a086984b75cf6aa02738531c2a better wording --- diff --git a/personal/_posts/2018-07-24-pointers-and-bytes.md b/personal/_posts/2018-07-24-pointers-and-bytes.md index f3c9133..636fa40 100644 --- a/personal/_posts/2018-07-24-pointers-and-bytes.md +++ b/personal/_posts/2018-07-24-pointers-and-bytes.md @@ -35,7 +35,7 @@ It would be beneficial to be able to optimize the final read of `y[0]` to just r C++ compilers regularly perform such optimizations as they are crucial for generating high-quality assembly.[^perf] The justification for this optimization is that writing to `x_ptr`, which points into `x`, cannot change `y`. -[^perf]: To be fair, the are *claimed* to be crucial for generating high-quality assembly. The claim sounds plausible to me, but unfortunately, I do not know of a systematic study exploring the performance benefits of undefined behavior such as this. +[^perf]: To be fair, the are *claimed* to be crucial for generating high-quality assembly. The claim sounds plausible to me, but unfortunately, I do not know of a systematic study exploring the performance benefits of such optimizations. However, given how low-level a language C++ is, we can actually break this assumption by setting `i` to `y-x`. Since `&x[i]` is the same as `x+i`, this means we are actually writing `23` to `&y[0]`.