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

[Jason Merrill]

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.

Jason