alt Hacker News> AND-masking does not really allow for producing the necessary traps for invalid accesses.
Why does it need to trap? Can't they just make it UB?
Specifying that invalid accesses always trap is going to degrade performance, that's not a 64-bit problem, that's a spec problem. Even if you define it in WASM, it's still UB in the compiler so you aren't saving anyone from UB they didn't already have. Just make the trapping guarantee a debug option only.
It's WASM. WASM runs in a sandbox and you can't have UB on the hardware level. Imagine someone exploiting the behavior of some browser when UB is triggered. Except that the programmer is not having nasal demons [1] but some poor user, like a mom of four children in Abraska running a website on her cell phone.
[1]: http://catb.org/jargon/html/N/nasal-demons.html