Incrementing volatiles?

["Matthias Urlichs" <smurf at noris dot de>]

Hi,

The following code, using egcs-current -O2 -fomit-frame-pointer

         unsigned int foo;    afoo() { foo++; }
volatile unsigned int bar;    abar() { bar++; }

  compiles, on ix86, to

afoo:   incl foo
        ret
abar:   movl bar,%eax
        incl %eax
        movl %eax,bar
        ret

But actually, it should be perfectly valid to compile both to code using
"incr". After all, both versions read the variable, do something with it,
and then write it out.

Is there a way to convince the optimizer to do this?

(The obvious solution, i.e. "(*(unsigned int *)&bar)++", doesn't count. ;-)

-- 
Matthias Urlichs
noris network GmbH