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<p class="MsoNormal"><span style="font-size:11.0pt">Hi all (CC some people who have been involved in this discussion already and Hans for clang 6 release discussion),<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">-Wtautological-constant-compare was introduced in r315614 to diagnose tautological comparisons against a type's maximum and minimum bounds. However, this warning can fire spuriously when a type's size is platform-dependent.
For example, libc++ has some generic code for which the warning fires on platforms where int and long have the same size; see
<a href="https://reviews.llvm.org/D39149">https://reviews.llvm.org/D39149</a> for my initial attempt to work around the warning, and then
<a href="https://reviews.llvm.org/D41368">https://reviews.llvm.org/D41368</a>, which just silences the warning where it's problematic.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">Unfortunately, this appears to be a pretty widespread problem. For example, Petr Hosek reported in
<a href="https://reviews.llvm.org/D39462">https://reviews.llvm.org/D39462</a> that he had to globally disable the warning when they rolled out a newer clang. Roman attempted to address this problem by having the warning take type size differences into account
in <a href="https://reviews.llvm.org/D39462">https://reviews.llvm.org/D39462</a>, but that's tricky to implement and hit some implementation roadblocks.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">I think shipping the warning in its current state in clang 6 is going to be problematic, because there are going to be many instances of generic code running into spurious warnings. At the very least, I think
the warning as-is shouldn't be part of -Wall. What are other people's thoughts on this issue?<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">Thanks,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">Shoaib<o:p></o:p></span></p>
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