| Issue |
139227
|
| Summary |
[Clang] Linker error at -O0 due to missing static const int definition, hidden at -O2
|
| Labels |
|
| Assignees |
|
| Reporter |
shzaiz
|
In `Clang 20.1.0`, a class with static const int members that are declared but not defined results in a linker error at `-O0`, but compiles successfully at `-O2`.
This seems to be due to constant propagation at higher optimization levels, which removes the need for symbol resolution, masking the fact that a required definition is missing.
This behavior differs from `MSVC`, which compiles successfully in both optimization levels.
Code:
```cpp
#include <map>
#include <vector>
using namespace std;
const pair<int, int> START = make_pair(0, 0);
class GridWorld {
public:
// change `const' to `constexpr', it will successfully execute
// or change compiler option with -O2
static const int NORTH = 123456, SOUTH = 1, EAST = 2, WEST = 3;
typedef pair<int, int> State;
GridWorld(int x = 0, int y = 0) {}
State state() { return make_pair(x, y); }
map<State, double> benefit_matrix;
void learn_benefit() {
GridWorld temp(0, 0);
for (auto action_state : temp.available_actions())
;
}
private:
int x, y;
vector<pair<int, State>> available_actions() {
vector<pair<int, State>> actions;
if (y != 0)
actions.push_back(make_pair(NORTH, make_pair(x, y - 1)));
if (y != 4)
actions.push_back(make_pair(SOUTH, make_pair(x, y + 1)));
if (x != 4)
actions.push_back(make_pair(EAST, make_pair(x + 1, y)));
if (x != 0)
actions.push_back(make_pair(WEST, make_pair(x - 1, y)));
return actions;
}
};
int main() {
GridWorld env = GridWorld(START.first, START.second);
env.learn_benefit();
return 0;
}
```
Reproduction Link: https://godbolt.org/z/dTdxWzMjP
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