Re: optimizations

[Reza Roboubi <reza at linisoft dot com>]

Andrew Pinski wrote:
> 
> What version of gcc?
> This seems like it was fixed at one point doing the 3.x series because
> it does not happen with 3.3 (prerelease) or 3.4 (experimental).

Ah. I am using gcc version 3.2. It's very good if this has been fixed under 3.3
and 3.4. 

I would still appreciate any comments regarding the status of these
optimizations. Are these new features, or are they old ones that temporarily got
broken during gcc 3.2?

What part of the gcc source tree deals with these optimizations?

Thanks again.

> 
> Thanks,
> Andrew Pinski
> 
> On Tuesday, Jan 14, 2003, at 12:35 US/Pacific, Reza Roboubi wrote:
> 
> > In the following code, it is clear that the return value of mm() can be
> > eliminated.  In fact, many optimizations are possible here.  Yet gcc
> > seems not
> > to be able to do these optimizations.  Below, I posted the assembly
> > code that
> > gcc generated (for the while() loop).
> >
> > I compiled this code with gcc -O2 -Wall.
> >
> > I was wondering if I am doing something wrong.  If not, then please
> > comment on
> > current gcc developments in this regard, and what it takes to add some
> > of these
> > features.
> >
> > Please also comment on how other compilers would compare with gcc in
> > this case.
> >
> > Are there any non-obvious remedies you have for this case?
> >
> > PS: Please tell me if I must report this as a gcc bug.
> >
> > Thanks in advance for any help you provide.
> >
> >
> > inline int mm(int *i)
> > {
> >         if((*i)==0x10){return 0;}
> >         (*i)++;return 1;
> > }
> >
> > int
> > main(){
> >
> >       int k=0;
> >       while (mm(&k)){}
> >       write(1,&k,1);
> >
> >       return 0;
> > }
> >
> >
> > Associated assembly code for the while() loop:
> >
> > 0x80483b0 <main+16>:  mov    0xfffffffc(%ebp),%eax
> > 0x80483b3 <main+19>:  xor    %edx,%edx
> > 0x80483b5 <main+21>:  cmp    $0x10,%eax
> > 0x80483b8 <main+24>:  je     0x80483c3 <main+35>
> > 0x80483ba <main+26>:  inc    %eax
> > 0x80483bb <main+27>:  mov    $0x1,%edx
> > 0x80483c0 <main+32>:  mov    %eax,0xfffffffc(%ebp)
> > 0x80483c3 <main+35>:  test   %edx,%edx
> > 0x80483c5 <main+37>:  jne    0x80483b0 <main+16>
> >

-- 
Reza Roboubi
IT Solution Provider: 
   Software Development; Data Servers; Embedded Devices.
www.linisoft.com