Path: utzoo!attcan!uunet!mcsun!cernvax!rbt
From: rbt@cernvax.UUCP (roberto divia)
Newsgroups: comp.os.os9
Subject: Re: Passing parameters by registers is bad use?!?!?
Keywords: C compiler, parameter passing
Message-ID: <2855@cernvax.UUCP>
Date: 11 Oct 90 07:23:24 GMT
References: <2823@cernvax.UUCP> <3555@rwthinf.UUCP> <3574@rwthinf.UUCP>
Organization: CERN, European Laboratory for Particle Physics
Lines: 17

This might go on forever... I have looked at some of my code (mostly written
for real time applications) and noticed how often I have used routines with
one or two input parameters and the output value. I also did some tests where
the same routine was called with parameters on stack and parameters in
registers and found that the second case is MUCH faster. My tests where
executed on a MC68030 (program and data caches). The simple fact of passing
one or two of 6 parameters (or more) into registers reduced the execution time
of 10 to 20 %. To see why, I tried different combinations. In particular, when
I turned OFF the data cache, the speed gain was much less (2, 3%). This
because the data region used by the program was somehow "extended" by the use
(or better - the abuse) of the data stack made during subroutine calls. Try
to believe...
-- 
|   Roberto Divia`      | Love at  first sight  is one of the greatest |
|   =============       | labor-saving devices the world has ever seen |
|  CERN :  European Laboratory for Particle Physics,  1211  Geneva  23 |
|  Switzerland (CH)                                                    |