> I code with SIMD as the target, and have special containers that pad memory to SIMD width...

I think this may be domain-specific. I help maintain several open-source audio libraries, and wind up being the one to review the patches when people contribute SIMD for some specific ISA, and I think without exception they always get the tail handling wrong. Due to other interactions it cannot always be avoided by padding. It can roughly double the complexity of the code [0], and requires a disproportionate amount of thinking time vs. the time the code spends running, but if you don't spend that thinking time you can get OOB reads or writes, and thus CVEs. Masked loads/stores are an improvement, but not universally available. I don't have a lot of concrete suggestions.

I also work with a lot of image/video SIMD, and this is just not a problem, because most operations happen on fixed block sizes, and padding buffers is easy and routine.

I agree I would have picked other things for the other two in my own top-3 list.

[0] Here is a fun one, which actually performs worst when len is a multiple of 8 (which it almost always is), and has 59 lines of code for tail handling vs. 33 lines for the main loop: https://gitlab.xiph.org/xiph/opus/-/blob/main/celt/arm/celt_...