[PATCHv3] Add a warning for invalid function casts

[Jason Merrill]

On Thu, Dec 7, 2017 at 3:48 PM, Bernd Edlinger
<bernd.edlinger@hotmail.de> wrote:
> On 12/06/17 23:35, Jason Merrill wrote:
>> On Fri, Dec 1, 2017 at 7:42 AM, Bernd Edlinger
>> <bernd.edlinger@hotmail.de> wrote:
>>> this version of the patch improves the heuristic check to take the
>>> target hook into account, to handle cases correctly when both or only
>>> one parameter is _not_ promoted to int.
>>
>> In looking at this, I discovered that the argument to
>> promote_prototypes should be the function type, not the parameter
>> type; the existing uses in the C++ front end were wrong.
>>
>
> Bah, sorry.
>
> Yes, it looks like there are at least two more target hooks that change
> the type promotion rules later-on: targetm.calls.promote_function_mode
> and PROMOTE_MODE.
>
> In the ada FE we pass NULL_TREE to promote_prototypes which seems to
> mean if the target wants type promotion in principle.  So it returns
> true if some function may promote, and false if no function promotes.
> At least this is how the sh-target handles this parameter.
> This is BTW the only target that uses the argument of this callback.
>
> So I would think for the purpose of this warning the following check
> should be sufficient:
>
>    if (INTEGRAL_TYPE_P (t1)
>        && INTEGRAL_TYPE_P (t2)
>        && TYPE_PRECISION (t1) == TYPE_PRECISION (t2)
>        && (TYPE_UNSIGNED (t1) == TYPE_UNSIGNED (t2)
>            || !targetm.calls.promote_prototypes (NULL_TREE)
>            || TYPE_PRECISION (t1) >= TYPE_PRECISION (integer_type_node)))
>
>
> What do you think?
> Is the patch OK with this change?

Yes.

Jason