[PATCH] C undefined behavior fix

[dewar@gnat.com]

<<Yes, thank you, that part was obvious already.  The question pertained
to the fact that nobody outside compiler-visible code was being handed
an address for b, and so the compiler could (if it wanted to) prove
under pretty broad assumptions that nobody could *find* b to make the
change in the first place.
>>

Suppose that a hardware emulator is used to change the value of b (IT
knows the address) at the point of:

>     >>>>>>>>> here b changes

The reason was precisely to test a different value for b. This should
work if b is volatile. So the compiler's proof is flawed. The whole
point of volatile is that ALL such proofs are forbidden for volatile
objects.