> we can validate if an inline assembly expression is safe by ... Ensuring that the assembly's effects are fully captured by the constraints. For example, if an assembly instruction modifies a register, then the constraints must capture that register mutation...

I mean, I'm not sure if LLVM parses the assembly (I strongly suspect it does, I remember inline GCC assembly allowed stuff like referencing variables in asm), shouldn't LLVM figure out that the asm modifies things its not supposed to?

If you clobber a register in asm the compiler stores something into, your code certainly won't work right.