On Fri, Jun 04, 2021 at 10:10:29AM -0700, Linus Torvalds wrote:

The compiler *cannot* just say "oh, I'll do that 'volatile asm
barrier' whether the condition is true or not". That would be a
fundamental compiler bug.

Yes.

Of course, we might want to make sure that the compiler doesn't go
"oh, empty asm, I can ignore it",

It isn't allowed to do that.  GCC has this arguable misfeature where it
doesn't show empty asm in the assembler output, but that has no bearing
on anything but how human-readable the output is.


Segher