From mboxrd@z Thu Jan  1 00:00:00 1970
From: Jeffrey A Law <law@cygnus.com>
To: jbuck@synopsys.com
Cc: steffend@glitch.physics.colostate.edu (Dave Steffen), egcs@cygnus.com
Subject: Re: EGCS vs GCC performance 
Date: Thu, 15 Jan 1998 16:30:00 -0000
Message-id: <3896.884803180@hurl.cygnus.com>
References: <199801131736.JAA04529@atrus.synopsys.com>
X-SW-Source: 1998-01/msg00475.html

  In message < 199801131736.JAA04529@atrus.synopsys.com >you write:
  > 
  > >    If anybody's interested, I just did a (very) informal performance
  > >    test between EGCS 1.0.1 and GCC 2.7.2. The test involved compiling
  > >    and executing some heavily-templated numerical code on a HP 715
  > >    running HP-UX 9.05.
  > ...
  > >    The result, in a nutshell, is that EGCS outperforms GCC
  > >    significantly in both compile-time and run-time.
  > 
  > HP, if I understand correctly, is the platform that has benefited the
  > most from the Haifa scheduler.
Yes.  If I remember right 8% or so was the average improvement due to
haifa alone (for FP intensive code).  With the alias analysis and other
HP opts that have gone in since gcc-2.7 20-25% improvment isn't unrealistic.

  > The story isn't as great on some other
  > platforms; ix86/Pentium performance seems to have actually gotten worse
  > in some cases according to several reports.  But I'm sure this will be
  > addressed soon.
Right.  Actually for the x86 the first thing we're being nailed by
is the alignment of doubles (at least that's my understanding).

We also need to throttle some of the loop opts to avoid holding too
many computable givs in registers through the life of a loop.  It was
a problem in older versions of gcc, but it's much more pronounced in
egcs because egcs does a much better job at finding GIVs than older
versions of gcc.

And scheduling problems.  The x86 port really needs some work before it'll
be generally profitable to enable instruction scheduling.

jeff