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]`.