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From: acn@cl.cam.ac.uk (Arthur Norman)
Newsgroups: comp.sys.acorn
Subject: Re: is it possible to port GNU-GCC-Compiler to Archimedes running RISC-OS ?
Message-ID: <1991Feb20.085225.11667@cl.cam.ac.uk>
Date: 20 Feb 91 08:52:25 GMT
References: <1809@tharr.UUCP> <5257@acorn.co.uk>
Reply-To: acn@cl.cam.ac.uk (Arthur Norman)
Distribution: comp
Organization: U of Cambridge Comp Lab, UK
Lines: 27


Owen Smith makes some observations about the speed of code generated
by the Norcroft compiler on an 88000 compared with GCC, and makes
deductions about what one could expect on the ARM.  It may be useful to
note that (a) the 88000 compiler is in a very early pre-release state
(pending sorting out the 88000 most exciting va_args convention!) and I
would expect to speed it up before release, (b) in particular it hardly
had any treatment of instructi0n scheduling, which on the 88000 is fairly
vital but which does not have any relevance on the ARM, (c) the ARM version
of ncc has a fairly large chunk of machine specific tuning and optimisation
that again the 88000 one mentioned did not.  Thus I do NOT believe one can
generalise and expect gcc/ARM to produce significantly better code than
ncc over a wide range of styles and quantities of code.  But I do hope
that if people can spot ways in which ncc could be persuaded to produce
5% smaller or 5% faster code ACROSS LARGE BODIES OF REALISTIC CODE and not
just in one tiny case they will forward the ideas into Acorn/ARM Ltd.
We have just about got ncc going on a mips machine, to the state where I
have only one time measurement, and at present I am uncertain of its
reliability, but that suggests that ncc is winning relative to gcc wrt
speed of compiled code and in this very first working version is only 1.5%
behind on code density - we will fix that up soon.  Furthermore on the
particular releasze of gcc involved the prohgram I most want to run
misbehaves (just slightly) when -O is specified, so until I have chased
that down & found a fixed gcc I am not really going to be able to quote
timings.
Cheers Owen!
     Arthur Norman