[cfe-commits] Patch: Add a warning for NULL used in arithmetic operations

[Richard Trieu]

On Thu, May 26, 2011 at 3:10 AM, Chandler Carruth <chandlerc at google.com>wrote:

> On Mon, May 2, 2011 at 5:48 PM, Richard Trieu <rtrieu at google.com> wrote:
>
>> Add warning when NULL constant value is used improperly in expressions.
>>
>>
> Some high-level comments:
>
> 1) Why only handle GNUNull null-pointer-constants? I think there is a good
> reason here (making them behave as much like nullptr as possible) but it
> would be good to document that in comments at least.
>
The other kinds of nulls are zero integer and c++0x nullptr.  Integral zero
is valid for these operations.  nullptr is a different type which already
produces an error in these cases.

>
> 2) What drives the set of invalid operations? I assume its those that
> nullptr would be invalid for? If so, can you provide standard citations
> against the draft standard? Also, is there no way to just turn on the C++0x
> errors for nullptr when we see the GNUNull in C++03, but down-grade them to
> warnings?
>
These operations are the ones where the null pointer would be used as an
integer instead of a pointer. I've also copied the test, but using nullptr
instead to show that they error in same places.

It should be possible to change the NULL into a nullptr and then run the
checks, but that would probably involve touching code in all the of
operation checking functions.  I feel that it would be better to keep this
code in one place instead of spread across so many functions.

>
> 3) Because these are warnings, we can't return ExprError; that changes the
> parse result.
>
Removed the early exit with ExprError.
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