Re: [rtl] Optimization question.

[wade <wade@xwin.net>]

On Sun, 12 Jul 1998, Oleg Subbotin wrote:

> Hello, everybody.
> I have this tiny example :
> 
> #define ONE 0x01
> 
> int fun ()
> {
>         volatile register temp=0;
> 
>         while ( temp&ONE ) {
>         /* Do something */
>         }
> }
> 
This does exactly what you told it to.  temp&ONE means you wanted to AND
them binary bit by bit,  What I think you may have wanted to do is a 
temp&&ONE which is a logical AND.
Randal
 
> And when I compile it with gcc -O2 -S I get this assembly code:
> 
> fun:
>         pushl %ebp
>         movl %esp,%ebp
>         subl $4,%esp
>         movl $0,-4(%ebp)
>         .align 4
> .L2:
>         movl -4(%ebp),%eax
>         testb $1,%al               <--Instead of logical AND gcc generate testb
>         jne .L2			   <--But for test==3,5,7... it will not work
>         leave			   <--as I expect it to
>         ret 
> 
> Does anybody knows how to avoid this?
> I absolutely have to compile the program with -O2 flag, but with this 
> "optimization" my program does not work. I am also very surprized by my
> discovery - this type of code is all over the Linux code, but it still
> works.
> 
> Thanks for any help.
> 
> Oleg.
> 
> --- [rtl] ---
> For more information on Real-Time Linux see:
> http://www.rtlinux.org/
> 

--- [rtl] ---
For more information on Real-Time Linux see:
http://www.rtlinux.org/