https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92367
Bug ID: 92367
Summary: spurious -Wunused-but-set-parameter warning with
constexpr if in a template function
Product: gcc
Version: 9.2.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: 60rntogo at gmail dot com
Target Milestone: ---
Created attachment 47171
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=47171&action=edit
g++ -v output
The code
template <bool b, typename T>
constexpr T example(T i)
{
if constexpr (b)
{
return i;
}
else
{
return 0;
}
}
int main()
{
example<false>(0);
}
compiled with
g++ example.cpp -std=c++17 -Wunused-but-set-parameter
yields
example.cpp: In instantiation of ‘constexpr T example(T) [with bool b = false;
T = int]’:
example.cpp:16:20: required from here
example.cpp:2:23: warning: parameter ‘i’ set but not used
[-Wunused-but-set-parameter]
2 | constexpr T example(T i)
| ~~^
The warning is raised even if example<true> is called in addition to
example<false>. It is not raised if the template parameter T is replaced by
int.
