Compilers and programming style (was Re: A question of style)

[Scott Amspoker]

In article <279 at dino.cs.iastate.edu> hascall at cs.iastate.edu (John Hascall) writes:
>}Just curious - what kind of code should be generated for the above
>}C fragment?
>
>   (using VAX-11 as an example)
>
>	  MOVL   @P,temp         ; move int pointed to by P into a throwaway
>      or
>          TSTL   @P              ; compare int pointed to by P to zero
>
>   If you've never written a device driver, you may not understand why
>   you would want to do this.

I've written plenty of device drivers and I still wouldn't do it.  I 
suppose that since device drivers are extremely implementation dependant
it probably wouldn't hurt to assume that the C semantics for
 
    *p;

would cause a TSTL instruction - especially if by experimentation you
discover that to be true on your particular compiler.  I just don't
recall reading that anywhere.  If I wanted to merely access a memory
location I would do something like

   dummy = *p;

But even then, some compilers might throw that away if dummy is dead
(which it probably is).


-- 
Scott Amspoker
Basis International, Albuquerque, NM
(505) 345-5232
unmvax.cs.unm.edu!bbx!bbxsda!scott