Re: [RFC PATCH] -Wmemset-transposed-args (PR middle-end/61294)

[Richard Biener <richard.guenther@gmail.com>]

On Wed, Jul 9, 2014 at 12:33 AM, Jason Merrill <jason@redhat.com> wrote:
> On 07/08/2014 12:38 PM, Carlos O'Donell wrote:
>>
>> What rationale would you give for not warning on 1-1?
>
>
> Because it's not likely to be a case of argument transposition; it's more
> likely to be an expression that just happens to evaluate to 0, which is fine
> as a length argument to memset.
>
>
> On 07/08/2014 01:31 PM, Jakub Jelinek wrote:
>>
>> On Tue, Jul 08, 2014 at 03:24:52PM -0400, Jason Merrill wrote:
>>>
>>> I don't think we want to warn about e.g. 1-1, only about literal 0.
>>
>>
>> Well, at least literal 0 and '\0'.
>
>
> Right, I consider '\0' to be a literal 0.
>
>
>> But in the C++ FE there isn't something like that.  Do you think we
>> shouldn't warn even if e.g. the last argument is a template parameter
>> that turns out to be 0, so warn only during parsing and check for literal
>> 0 and not warn again during instantiation?
>
>
> Yes, that's what I think.
>
>
>> Any suggestions how to find out
>> if it was literal 0 or something that folded to 0 in the C++ FE?
>
>
> I suppose we could use an INTEGER_CST distinct from the one in
> TYPE_CACHED_VALUES for raw 0, with a TREE_LANG_FLAG set.

Ick.  (please no - at least make sure it doesn't survive anywhere to the
middle-end, like fold or gimple).

Richard.

> Jason
>