Re: Performace problems with gcc 3.0.4

["Paulo Pinto" <paulo dot pinto at altitude dot com>]

My friend has an Athlon 1400 Mhz

Paulo Pinto

----- Original Message -----
From: "Dan Nicolaescu" <dann@godzilla.ICS.UCI.EDU>
To: "gcc" <gcc@gcc.gnu.org>
Cc: "Joe Buck" <Joe.Buck@synopsys.com>; "Paulo Pinto"
<paulo.pinto@altitude.com>
Sent: Tuesday, March 19, 2002 5:57 PM
Subject: Re: Performace problems with gcc 3.0.4


> Joe Buck wrote:
>
> >  > According to [a friend], the following code is about
> >  > 50% slower than the version without structs.
> >  >
> >  > He was tried the ICC (Intel compiler) and it
> >  > generates the same code for the two cases but
> >  > gcc does not. He played with all optimization
> >  > flags that affect numeric code but to no avail.
> >  >
> >  > Does anyone know what might be the problem ?
> >
> >  Yes, it's a well-known problem with gcc.  Structs get committed to
memory
> >  too early.  Some compilers are able to split apart structs and treat
their
> >  members as independent scalar variables; gcc can only do this for
structs
> >  or classes with a single member.
>
> That is true, but it might not be the problem in this case.
> On SPARC both the assembly generated by gcc-3.0.4 -O2 is identical.
> So you might hit an x86 specific problem...