https://gcc.gnu.org/bugzilla/show_bug.cgi?id=120121
Bug ID: 120121
Summary: Comparison of integer expressions of different
signedness not detected
Product: gcc
Version: 15.1.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: stefano.d at posteo dot de
Target Milestone: ---
Created attachment 61326
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=61326&action=edit
Not detected comparison of different signedness
There is a not detected integer promotion when two variables are multiplied and
the result is not stored into a variable.
This compiles with -Wall -O1 -Wextra -Wshadow -Weffc++ -Wno-long-long -pedantic
-pedantic-errors -std=c++14
```
#include <cstdint>
bool square_less_than_method_A(uint16_t a, uint64_t b) {
// a * a does integer promotion
return (a * a < b);
}
int main(int, char**) {
return 0;
}
```
See also: https://godbolt.org/z/jz8Ka8asn
When the result is assigned into a variable, GCC detects the comparison of
integer expressions of different signedness:
```
#include <cstdint>
bool square_less_than_method_B(uint16_t a, uint64_t b) {
const auto a_squared = a * a;
return a_squared < b;
}
int main(int, char**) {
return 0;
}
```
The error is correctly reported:
```
<source>: In function 'bool square_less_than_method_B(uint16_t, uint64_t)':
<source>:5:22: warning: comparison of integer expressions of different
signedness: 'const int' and 'uint64_t' {aka 'long unsigned int'}
[-Wsign-compare]
5 | return a_squared < b;
| ~~~~~~~~~~^~~
```
See also: https://godbolt.org/z/dfY749vdd
