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From: jim@cs.strath.ac.uk (Jim Reid)
Newsgroups: net.lang.c
Subject: Re: Datalight faster than 4.2, why?
Message-ID: <131@stracs.cs.strath.ac.uk>
Date: Wed, 14-May-86 07:48:57 EDT
Article-I.D.: stracs.131
Posted: Wed May 14 07:48:57 1986
Date-Received: Sat, 17-May-86 04:12:00 EDT
References: <989@dataioDataio.UUCP>
Reply-To: jim@cs.strath.ac.uk (Jim Reid)
Organization: Department of Computer Science at Strathclyde University, UK.
Lines: 35

In article <989@dataioDataio.UUCP> bjorn@dataio.UUCP writes:
>	The state-of-the-art in compilers has progressed on PCs,
>	so why hasn't anyone come up with a better compiler for
>	UNIX, or have I just not heard of it?
>
>For your information I'm running UNIX 4.2bsd with the standard C 
>compiler on a VAX 11/750, and Datalight C 2.04 on an IBM PC/AT under
>MSDOS 3.0.  The PC takes 5 minutes 26 seconds to compile 7605 lines of 
>code in 29 files (plus 735 lines of header in 13 files), whereas the unloaded
>VAX (load average 1.13) takes 8 minutes 30 seconds.  All the outside 
>influences were indentical: debugging, optimization, etc.

Whoopee! I'm glad someone has proved that an AT - floppy disks and all? -
is faster than a VAX. Maybe now I can convince folk it's a good idea to
scrap our VAX for an AT!!! :-) :-) :-) :-) :-)

Comparisons like that are *totally meaningless* - What about the quality of
the generated code? What "optimisations" do the compilers perform? Do both
produce much the same symbolic information for debugging? What's involved in
linking object modules in the two progams? How many passes over the source
code/expanded code/"parse trees" does each compiler do? The 4BSD compiler has
at least 5 - 6 if you count linking. First there's the preprocessor, then
the compiler proper has probably two passes, the assembler has another two
for good measure (depending on how you look at the assembler). Then there's
your configuration - how much memory does each system have? How much core
does each compiler use/need? How much paging or swapping goes on during
compilation? How much disk traffic - intermediate files etc - is done?

Granted, your AT compiler might have faster algorithms for symbol table lookup
and the like, but the only conclusion that can be drawn from the numbers you
gave is that for the conditions you describe, your AT C compiler is faster.
It doesn't follow that both compilers or CPUs are doing the same amount of
work, so making comparisons or drawing conclusions are pointless.

		Jim