[Patch] Disable -Wtaulological-compare for substituted template types

[David Blaikie]

Cool - perhaps add a test case for the non-type template parameter case as
well? Though it's not really necessary. Up to you.


On Fri, Nov 1, 2013 at 2:54 PM, Richard Trieu <rtrieu at google.com> wrote:

> Committed in r193887 and r193888
>
>
> On Fri, Nov 1, 2013 at 1:02 PM, David Blaikie <dblaikie at gmail.com> wrote:
>
>>
>>
>>
>> On Fri, Nov 1, 2013 at 12:15 PM, Arthur O'Dwyer <
>> arthur.j.odwyer at gmail.com> wrote:
>>
>>> On Thu, Oct 31, 2013 at 5:52 PM, Richard Trieu <rtrieu at google.com>
>>> wrote:
>>> > On Thu, Oct 31, 2013 at 4:25 PM, David Blaikie <dblaikie at gmail.com>
>>> wrote:
>>> >>
>>> >> Could we just restrict these warnings to only be done on template
>>> >> patterns, not template specializations? (I know Ted's had some
>>> concern about
>>> >> doing work on template patterns in the past because he believed that
>>> might
>>> >> create too much work analyzing templates that are never instantiated,
>>> >> though)
>>> >
>>> > I think that would be possible and a cleaner way of approaching this.
>>> > Currently, Clang warns in both template patters and specializations.
>>>  That
>>> > means if you have :
>>> >
>>> > template<int Num>
>>> > bool greater(unsigned Val) {
>>> >   return Val >= 0;
>>> > }
>>> >
>>> > ... greater<0>(42); ...
>>> > ... greater<1>(42); ...
>>> > ... greater<2>(42); ...
>>> >
>>> > There would be four warnings on the return line.  Ignoring the three
>>> > warnings in the specializations and only showing the one from the
>>> template
>>> > pattern would be best on cutting down the noise.
>>>
>>> Only for -Wtautological-compare, though, right?
>>>
>>> I imagine that there are plenty of warnings that would be useful to
>>> produce during template instantiation, but impossible to detect by
>>> just looking at the pattern (without checking dependent
>>> types/expressions). A trivial example would be
>>> -Wuninitialized for this code:
>>>
>>>     template<typename T> T newval() { T t; return t; }
>>>
>>> Here, newval<int>() has undefined behavior, but newval<std::string>()
>>> is perfectly correct.
>>>
>>> So whereas -Wtautological-compare empirically gives almost 100% false
>>> positives on dependent expressions, -Wuninitialized probably gives
>>> 100% *true* positives.
>>
>>
>> Certainly. There are many warnings in each of these buckets, but
>> generally a given warning falls into only one - either it should be done on
>> instantiations or patterns. (there are some similar issues with macros and
>> other things (sizeof/decltype of implementation-provided types, etc))
>>
>
>
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