https://gcc.gnu.org/bugzilla/show_bug.cgi?id=117382
Bug ID: 117382
Summary: Conversion of integral to enumeration outside of range
is UB but works in consteval context
Product: gcc
Version: 14.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: konstantin.vladimirov at gmail dot com
Target Milestone: ---
Consider this code:
---
enum class MyPrettyEnum {
Value = 0,
};
consteval int process(int n) {
MyPrettyEnum E = static_cast<MyPrettyEnum>(n);
return static_cast<int>(E);
}
constexpr int x = process(10);
---
in C++23
[expr.static.cast] / 10
If the enumeration type does not have a fixed underlying type, the value is
unchanged if the original value is within the range of the enumeration values
(9.7.1), and otherwise, the behavior is undefined.
[expr.const] / 5
An expression E is a core constant expression unless the evaluation of E,
following the rules of the abstract machine (6.9.1), would evaluate one of the
following:
[...]
— an operation that would have undefined behavior
So this shall be prohibited.
