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From: torek@elf.ee.lbl.gov (Chris Torek)
Newsgroups: comp.lang.c
Subject: Re: Func Protos with K&R Func Defs
Message-ID: <10714@dog.ee.lbl.gov>
Date: 7 Mar 91 03:42:34 GMT
References: <1991Feb28.021715.18153@athena.mit.edu> <15354@smoke.brl.mil> <MLT9QB7@xds13.ferranti.com> <1991Mar2.181953.15401@athena.mit.edu> <BPX9AT9@xds13.ferranti.com>
Reply-To: torek@elf.ee.lbl.gov (Chris Torek)
Organization: Lawrence Berkeley Laboratory, Berkeley
Lines: 34
X-Local-Date: Wed, 6 Mar 91 19:42:35 PST

In article <BPX9AT9@xds13.ferranti.com> peter@ficc.ferranti.com
(Peter da Silva) writes:
>So you're saying that the compiler is not allowed to take advantage of the
>prototype information and use (for example) callee saves or special LINK
>instructions when calling prototyped functions?

This statement is correct (in a strict logical sense), but all the
implications it makes are wrong.  That is, the statement

	[compiler treats prototyped functions specially] implies
		[compiler may not take advantage of...]

is true but only because the clause [compiler treats prototyped
functions specially] is false.  Aside from default promotions,
prototyped functions and non-prototyped functions are treated
identically.  In particular, the compiler make take advantage of
special LINK or RET instructions for non-prototyped functions as
well as for the prototyped versions.

The only special case is varargs functions, which *must* be declared
using the new prototype varargs syntax.  All other functions may be
assumed to take fixed argument lists.  In other words,

	f(fmt, a1, a2, a3, a4, a5) char *fmt; {
		printf(fmt, a1, a2, a3, a4, a5);
	}
	...
		f("%d\n", 3);

is illegal, because the caller did not supply the proper number and
type of arguments.
-- 
In-Real-Life: Chris Torek, Lawrence Berkeley Lab EE div (+1 415 486 5427)
Berkeley, CA		Domain:	torek@ee.lbl.gov