https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77876
Bug ID: 77876
Summary: -Wbool-operation rejects useful code involving '~'
Product: gcc
Version: 7.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: eggert at gnu dot org
Target Milestone: ---
GCC's recently-added -Wbool-operation flag rejects useful code like this:
#include <time.h>
enum { BILLION = 1000 * 1000 * 1000 };
time_t foo (time_t s, int res) { return s & ~ (res == 2 * BILLION); }
This is a simplified version of Gnulib code using '~' that runs afoul of
-Wbool-operation; see the bug report here:
http://lists.gnu.org/archive/html/bug-gnulib/2016-10/txtbxk_mHAW_p.txt
Rather than contort user code to pacify this misguided warning, I suggest
making the warning more useful. The fundamental bug here is not applying ~ to a
boolean; it's storing ~x into a boolean. More generally, the problem occurs
when converting an expression that GCC can't prove to be 0 or 1 to bool. GCC
should check for that instead. This would catch not only thinkos with ~ and ++
and --, but also similar thinkos involving other integer and floating-point
operations. And it would correctly accept the Gnulib code.
