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From: darin@nova.laic.uucp (Darin Johnson)
Newsgroups: comp.sys.amiga
Subject: Re: C versus Assembly, which one?
Message-ID: <264@laic.UUCP>
Date: 20 Jun 88 18:34:22 GMT
References: <1968@uhccux.uhcc.hawaii.edu> <4508@killer.UUCP>
Sender: news@laic.UUCP
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In article <4508@killer.UUCP>, elg@killer.UUCP (Eric Green) writes:
> In particular, some of the RISC
> compilers generate code that keep calculated addresses around, and all of the
> RISC compilers seem to make every attempt to keep most-common-used variables
> in registers (in fact, the Pyramid 90x compiler totally ignores the "register"
> declarators, as far as I can tell -- at least, when you have fewer than 16
> local variables and 16 parameters).

This should be a feature of any compiler that optimizes.  I have been a
teaching assistant for C and compiler classes, and am amazed at the number
of people who swear that 'register' is a direct order to the compiler
("Gee, no wonder it doesn't work, you have 17 register variables...").
I was absolutely flabbergasted when I looked at the output of one of the
early Lattice compilers (I can't verify since I no longer have it).  It would
NEVER place automatic variables into registers UNLESS it was declared as 
'register' (it would use registers for temporaries, thank heavens).  I would
also get error messages if I used an excessive amount of register declarations.
For the money I paid, I would have expected the compiler to figure out on its
own that something could be put into a register without a 'hint'.

(Actually, when I wrote a compiler for the Pyramid, I thoroughly tested out
the existing C and Pascal assembly outputs.  You have to go to a lot of work
just to get a variable that isn't in a register!!  If the 16 local registers
were allocated, it would use any unused parameter registers, etc. etc.)

Darin Johnson (...pyramid.arpa!leadsv!laic!darin)
              (...ucbvax!sun!sunncal!leadsv!laic!darin)
	"All aboard the DOOMED express!"