https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95148
Bug ID: 95148
Summary: -Wtype-limits always-false warning triggered despite
comparison being avoided
Product: gcc
Version: 10.1.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: eyalroz at technion dot ac.il
Target Milestone: ---
Consider the following program:
#include <type_traits>
int main() {
unsigned x { 5 };
return (std::is_signed<decltype(x)>::value and (x < 0)) ? 1 : 0;
}
when compiling it with GCC versions 11.0 20200511, 10.1, 9.2.1, 8.3.0, I get
the warning:
a.cpp:5:52: warning: comparison of unsigned expression < 0 is always false
[-Wtype-limits]
I should not be getting this warning, because when x is unsigned, the
comparison is never performed, due to the short-circuit semantics of `and`.
This can be easily determined by the compiler - and probably is. No less
importantly, the author of such a line in a program clearly specified his/her
intent here with this check.
clang doesn't seem to issue a warn inf does come to pass.
