[RFC] PR61300 K&R incoming args

[Richard Biener]

On June 2, 2014 11:30:20 PM CEST, "Joseph S. Myers" <joseph@codesourcery.com> wrote:
>On Mon, 2 Jun 2014, Florian Weimer wrote:
>
>> On 05/31/2014 08:56 AM, Alan Modra wrote:
>> 
>> > > It's fine to change ABI when compiling an old-style function
>> > > definition for which a prototype exists (relative to the
>> > > non-prototype case).  It happens on i386, too.
>> > 
>> > That might be so, but when compiling the function body you must
>assume
>> > the worst case, whatever that might be, at the call site.  For K&R
>> > code, our error was to assume the call was unprototyped (which
>> > paradoxically is the best case) when compiling the function body.
>> 
>> Is this really a supported use case?  I think I remember tracking
>down a bug
>> which was related to a lack of float -> double promotion because the
>call was
>> prototyped, and the old-style function definition wasn't.  This would
>have
>> been on, ugh, SPARC.  I think this happened only in certain cases
>(float
>> arguments, probably).
>
>ISO C (right back to C90) requires a prototype in scope if a variadic 
>function, or a function whose definition has prototyped argument types 
>changed by the default argument promotions (such as float and short),
>is 
>called.
>
>It probably makes sense by now to enable
>-Wimplicit-function-declaration 
>by default, though that won't catch cases where the file with the 
>unprototyped call has a non-prototype declaration such as "int foo();".

There is an old patch of mine warning for this case...  Google for -Wunprototyped-calls

Richard.