[PATCH] D38101: [Sema] Diagnose tautological comparison with type's min/max values

[Roman Lebedev via cfe-commits]

On Fri, Oct 13, 2017 at 1:22 AM, Richard Smith <richard at metafoo.co.uk> wrote:
> On 12 October 2017 at 15:11, Roman Lebedev via Phabricator via cfe-commits
> <cfe-commits at lists.llvm.org> wrote:
>>
>> lebedev.ri reopened this revision.
>> lebedev.ri added a comment.
>> This revision is now accepted and ready to land.
>>
>> Reverted due to http://bb9.pgr.jp/#/builders/20/builds/59 that i don't
>> currently know how to deal with.
>> It is really sad that i failed to encounter it during testing.
>
>
> I see three issues there:

> 1) A warning in this code due to missing parentheses around a ^ operator.

> 2) This code generating correct warnings in the libc++ test suite.
Yes, this one is the problem.

I'm honestly not sure about these comparisons with
std::numeric_limits<...>::{min,max}()
They is similar to what Nico Weber (CC'd, just in case) is raising in
post-review mail in
https://lists.llvm.org/pipermail/cfe-commits/Week-of-Mon-20171009/206427.html
I personally would very much prefer to have the warning, as explained
in the follow-up mail.

> You could ask EricWF (cc'd) to look at those and either fix them or turn the warning
> flag off for libc++'s tests.
Eric: could you *please* look into that? :)
That is way too deep to change without prior knowledge about the code i think.

> 3) A stage2 / stage3 comparison failure in CGAtomic.cpp. That's pre-existing
> and nothing to do with your change.

Roman.