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: <2820@cernvax.UUCP>
Date: 27 Sep 90 06:19:14 GMT
References: <3537@rwthinf.UUCP>
Organization: CERN, European Laboratory for Particle Physics
Lines: 18

Sorry, I tend to disagree. It is true that allocating two registers for
parameter passing means some overload to the executable code but on the
other hand it is *MUCH* faster to do things this way. I did some tests
with a MC68030 and the same routine called with parameters in registers
was 10-15% faster then the equivalent called with parameters on the
stack. This comes for two main reasons:

1) the stack push/pop/stackPointerRearrangement takes time;
2) bigger is the data area used by the code is and easier is to have a
   cache miss (this in case of processors with data caches).

The Microware convention of "caller saves" reduces the overhead of registers
swapping/saving to the minimum necessary, so...
-- 
|   Roberto Divia`      | Love at  first sight  is one of the greatest |
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|  CERN :  European Laboratory for Particle Physics,  1211  Geneva  23 |
|  Switzerland (CH)                                                    |