Re: gEDA-user: Icarus Verilog building from CVS

[Dave McGuire <mcguire-atMUNGEDneurotica_dot_com>]

On Aug 6, 2004, at 11:44 PM, Al Davis wrote:
>>   Despite its popularity in the x86 world, GCC generates
>> horrid code on most, if not all, modern RISC platforms.  The
>> vendor-supplied compilers represent a tremendous amount of
>> in-the-know optimization and well-funded development that is
>> specific to their processor architectures.
>
> Really????

   Really. :)

> A few years ago, when I had access to a bunch of machines and a
> bunch of compilers I tried ACS (precursor to Gnucap) on all of
> them, with both GCC and the native one if possible.  The only
> one that had any significant difference was Sun's.  The Sun
> compiler was about 20% slower than GCC.  Has Sun's compiler
> improved that much, or has GCC gotten that much worse?  Perhaps
> Sun's compiler is better in some cases, and GCC better in
> others?

   That's certainly possible.  I have enough data points, however, that 
I don't even bother to install GCC on my Solaris systems anymore.

   Now bear in mind, this is coming from a long-time GCC lover.  Back In 
The Day(tm), I remember the very first thing to do on any new VAX 
system (running either VMS or UNIX) was to install GCC because it 
generated code that was much faster.  The same went for M68K-based 
Suns...GCC produced much, much faster executables than the 
vendor-supplied compiler.  That said, however, M68K and VAX are 
*extremely* CISC processors, designed to support compilers from the 
ground up.  GCC's initial development was on processors like 
that...Very CISC architectures, and that's where it really seems to 
shine, even today.

   (except, of course, for all the non-standard crap that it allows that 
many people unknowingly or uncaringly use, resulting in nonportable 
code)

   But try it on a MIPS, SPARC, or other modern RISC or post-RISC 
architecture and things don't look so good.  I've not done extensive 
reading on this, but I'm told that the inclusion of IBM's Haifa 
instruction scheduler in GCC a few years ago helped matters for RISC 
architectures, but the situation still gives me that "not so fresh" 
feeling.

> Having said that...  Looking at the assembly code for C++, I see
> that they are still missing some significant optimizations that
> are not possible in C.

   Hmm.  I'm not much into C++ (I'm a C guy) so I can't speak to that.  
I'd love to see some examples though.

         -Dave

--
Dave McGuire             "...it's a matter of how tightly
Cape Coral, FL             you pull the zip-tie."       -Nadine Miller