Func Protos with K&R Func Defs

[Peter da Silva]

In article <1991Mar2.181953.15401 at athena.mit.edu> scs at adam.mit.edu writes:
> Doug's statement is true, without exception, and reflects clear
> language in X3.159 (which I have quoted from in two previous
> articles on this subject), which defines exactly what is required
> for two function types to be compatible.

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 conflicts with...

> Secondly, there is no reason to use
> the less efficient calling sequence for old functions; the
> "newer," presumably more efficient (though not admitting of
> variable numbers of arguments) calling sequence can and should be
> used.

I don't believe this statement is true. If there is no prototype is
in scope, the compiler cannot make any assumption about the calling
sequence: it may be dealing with older code that uses a pre-ANSI method
of handling variadic functions, for example. For that matter the customer
might be working with older, pre-ansi libraries without source code
available.

> Efficiency is, after all, the most important
> consideration, and the main reason prototypes were adopted.
> (Don't buy this line that they're for checking function call
> consistency across source files, "for your convenience."  If
> they're for your convenience, then why do you have to work to
> supply them?)

It's not just a matter of "convenience". You need to have function
prototypes to generate correct code in the general case, due to (among
other things) the common use of uncast null pointer constants in
function calls and other vaxisms that depend on sizeof(int) ==
sizeof(char *).

Every other algol-type language I know of, even the execrable PL/M, does
require full prototypes for all functions. The compromise in ANSI C is
a reasonable compromise with current usage, and a long-needed enhancement
to the language.

In an environemnt where things like X-windows are accepted as the best
that we can do, efficiency arguments for prototypes must be taken with
a grain of salt.
-- 
Peter da Silva.  `-_-'  peter at ferranti.com
+1 713 274 5180.  'U`  "Have you hugged your wolf today?"