Path: utzoo!utgpu!jarvis.csri.toronto.edu!clyde.concordia.ca!uunet!tut.cis.ohio-state.edu!unmvax!bbx!bbxsda!scott
From: scott@bbxsda.UUCP (Scott Amspoker)
Newsgroups: comp.lang.c
Subject: Re: Compilers and programming style (was Re: A question of style)
Message-ID: <539@bbxsda.UUCP>
Date: 10 Jan 90 16:01:02 GMT
References: <1989Dec22.100135.2903@gdt.bath.ac.uk> <4367@rtech.rtech.com> <1989Dec31.153241.16479@gdt.bath.ac.uk> <649@codonics.COM> <1990Jan5.100042.26760@gdt.bath.ac.uk> <2283@dataio.Data-IO.COM> <534@bbxsda.UUCP> <279@dino.cs.iastate.edu>
Reply-To: scott@bbxsda.UUCP (Scott Amspoker)
Organization: Basis International,  Albuquerque, NM
Lines: 35

In article <279@dino.cs.iastate.edu> hascall@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