But a division that traps because you divide by zero would prevent previous observable behavior from happening when hoisted above it. So it is not about the division itself but about the indirect effect on other behavior that can be observed.

Compilers already understand this: For example, they would not hoist a potentially trapping operation such as a division above a function call. The issue is that they did not apply this rule also to volatile accesses, but LLVM now does because this was fixed.