From: Daniel Phillips <phillips@arcor.de>
To: Andrew Morton <akpm@digeo.com>,
       Arnaldo Carvalho de Melo <acme@conectiva.com.br>
Subject: GCC speed (was [PATCH] Isapnp warning)
Date: Sun, 22 Jun 2003 15:22:29 +0200
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Cc: cw@f00f.org, torvalds@transmeta.com, geert@linux-m68k.org,
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Hi Andrew,

On Sunday 22 June 2003 04:17, you wrote:
> Compared to 2.95.3, gcc-3.3 takes 1.5x as long to compile, and produces a
> kernel which is 200k larger.
>
> It is simply worthless.

Recently, we did an unscientific but nonetheless informative tour through 
various optimization and compiler version questions here:

   http://marc.theaimsgroup.com/?t=105167074500002&r=3&w=2
   [RFC][PATCH] Faster generic_fls

As a result, my general impression is GCC 3.2 (and, I presume, GCC 3.3 as 
well) comes out better than 2.95.3 in terms of binary performance on x86.  I 
seem to recall there was one case in one algorithm variation on one procesor 
type where 2.95.3 won marginally, and otherwise GCC 3.2 took the trophy every 
time, sometimes by a significant margin.  I was able to get satisfactory 
performance in terms of size as well, by tweaking compile options.  (In 
general, just mindlessly setting O3 seems to work well.)

So I like GCC 3.2 in terms of code quality, at least for the limited set of 
things I've tested, but that's not the only consideration.  Current GCC is a 
whole lot better in terms of C99 compliance and produces better warnings.

As for compilation speed, yes, that sucks.  I doubt there's any rational 
reason for it, but I also agree with the idea that correctness and binary 
code performance should come first, then the compilation speed issue should 
be addressed.  I hope the gcc team does make it a priority at some point.  
For my own part, I'm putting together a cluster to address the compilation 
speed issue, i.e., I don't really care about it.  Even a dual PIII turns in 
satisfactory results in that regard, or a single K7.

Regards,

Daniel

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