https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113852
Bug ID: 113852
Summary: -Wsign-compare doesn't warn on unsigned result types
Product: gcc
Version: 14.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: admin at computerquip dot com
Target Milestone: ---
I haven't quite figured out the pattern here so the title may not be great.
Some code may help explain better: https://godbolt.org/z/d8cqd1WqP
```
#include <iostream>
#include <limits>
#include <cinttypes>
int main()
{
uint16_t a1 = std::numeric_limits<unsigned short>::max();
uint16_t a2 = std::numeric_limits<unsigned short>::max();
/* a1 * a2 should be 4294836225 in math terms */
uint64_t a3 = 4294836225;
/*
* The result of (a1 * a2) is of type int and the result is negative.
* (a1 * a2) ends up as some bogus high number because the common
* type here ends up as uint64_t and sign-extension occurs.
*/
if ((a1 * a2) > a3) {
std::cout << "this will print\n";
}
}
```
Some observations I've noticed:
* If either a1 or a2 are constexpr, the warning will occur.
* This used to warn up until 8.1.
* Clang also doesn't warn here but MSVC will with /W3 or higher.
* This seems like a slight variation of
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101645
