On Sat, 12 Dec 2015, Matthew Fortune wrote:
> > > * config/mips/mips.c (mips_promote_function_mode): New function.
> > > (TARGET_PROMOTE_FUNCTION_MODE): Define as above function.
> > > (TARGET_PROMOTE_PROTOTYPES): Remove.
>
> I'm OK with this change on the basis that MIPS has been providing stronger
> guarantees than required by the various standards. I.e. after this change
> MIPS will have undefined behaviour for a mismatch in types between a
> call to an un-prototyped function and its definition:
Indeed this is exactly what the current ISO C language standard mandates
-- if an unprototyped call is made to a function whose definition has been
prototyped and the types of the arguments after promotion are incompatible
with the types of the respective parameters, then behaviour is undefined.
> extern void foo();
>
> void caller(int a)
> {
> foo(a);
> }
>
> --
>
> void foo(short a)
> {
> // the value of 'a' can be out of range of a short because the caller
> // did not get the right type for the argument.
> }
Which is exactly the case with the piece of code you quoted. Behaviour
of this code would be defined if the `a' parameter of `foo' was of the
`int' type. See Section 6.5.2.2 "Function calls", clause 6, for details.
Maciej
