[jakobegger]

But what about things like non-aligned memory access (allowed on x86, not allowed on ARM)? Porting code across architectures can't be as easy as just swapping LLVM backends, when not even recompiling the code is sufficient.

[willvarfar]

Modern ARMs are just fine with unaligned access.

There will be ISAs sufficiently different that you cannot make bitcode generated when targetting one not be massaged to fit another, but they are not mainstream. The mainstream are all increasingly similar 64-bit targets.