https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91083
Bug ID: 91083
Summary: inconsistent -Wsign-compare warnings
Product: gcc
Version: 9.1.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: karol.wozniak at linuxmail dot org
Target Milestone: ---
following code sample
template <typename T>
struct numeric_limits;
template<>
struct numeric_limits<long>
{
static constexpr long
max() noexcept { return 0x7fffffffffffffffL; }
};
int main() {
return 42ul > numeric_limits<long>::max();
}
compiled with: g++-9 prog.cc -Wall -Wextra
raises sign-compare warning (https://wandbox.org/permlink/zW28qdCjM3hHPtMd)
but...
- adding optimization: g++-9 prog.cc -Wall -Wextra -O2 -march=native
removes the warning (https://wandbox.org/permlink/Z0GpP3JvunbpKqwO)
- creating helper value to store numeric_limit turns on warning once again in
optimized code (https://wandbox.org/permlink/94s4PEuJLlhKviye)
int main() {
auto m = numeric_limits<long>::max();
return 42ul > m;
}
- making helper value const... removes warning
(https://wandbox.org/permlink/Z0GpP3JvunbpKqwO)
warning was not raised in gcc-8 (https://wandbox.org/permlink/3yKmF2OVJ3FBIPye)
