[Bug c++/68052] No printf format warnings in C++ code for macro in system headers

["manu at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68052

--- Comment #5 from Manuel López-Ibáñez <manu at gcc dot gnu.org> ---
(In reply to Olivier Blin from comment #3)
> Quoting Martin Sebor's answer from the gcc-help mailing list:
> https://gcc.gnu.org/ml/gcc-help/2015-10/msg00128.html

What Martin describes there is a different bug that occurs when there is a
whole stack of macro expansions (which is not the case in the original
testcase). My guess is that it is https://gcc.gnu.org/PR52998

Most of the bugs in the macro unwinder are known and triaged, but no one has
stepped up to fix them. See I) at https://gcc.gnu.org/wiki/Better_Diagnostics
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From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug c/68067] Wrong constant folding
Date: Fri, 23 Oct 2015 09:35:00 -0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?idh067

--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
Yep.  Btw, what happens is that we see

 if (tem - 1 != 2147483647)

and that is obviously always true unless tem - 1 wraps from -2147483648 to
2147483647 which would invoke undefined behavior.