rend() creates a pointer with offset -1. This is UB, according to the C++ standard: https://eel.is/c++draft/expr.add#4:
When an expression J that has integral type is added to [...] an
expression P of pointer type, the result has the type of P.
... if P points to a (possibly-hypothetical) array element i of an
array object x with n elements [...] the expressions P + J and J + P
(where J has the value j) point to the (possibly-hypothetical) array
element i+j of x if 0≤i+j≤n [...]
Otherwise, the behavior is undefined.
Also, it is unclear why the functions exist at all, when stdlib utils such as std::reverse_iterator{it} or std::views::reverse can be used out of the box.
So remove them, along with the ubsan suppressions, that are no longer used.
I’ve tagged this a refactor, because the code was always dead (unused outside of tests). And since commit 2925bd537cbd8c70594e23f6c4298b7101f7f73d it was completely dead. Also, I could not find a sanitizer that detects this type of UB.
