| Issue |
135508
|
| Summary |
[clang-tidy] Check request: bugprone-union-inactive-member-access
|
| Labels |
clang-tidy
|
| Assignees |
|
| Reporter |
denzor200
|
Needs a check that will find a reading of a union's field which was executed after another field has been written which remains active.
EXAMPLE:
```
union SimpleUnion {
int x;
double y;
};
void process() {
SimpleUnion u;
u.x = 10;
std::cout << "x = " << u.x << std::endl; // OK
u.y = 3.14;
std::cout << "y = " << u.x << std::endl; // BAD - looks like a typo, are you meaning `std::cout << "y = " << u.y`??
}
```
In the case when the union's trick used for obtaining a value of another type by reinterpreting the representation of an object, the check will suggest to use `std::memcpy` or even `std::bit_cast` if it's available. The efficiency would remain the same - compilers know how to optimize both of them.
BEFORE:
```
template<typename T>
T perform_type_punning(std::ptrdiff_t offset)
{
union {
T memptr;
std::ptrdiff_t offset_;
};
offset_ = offset;
return memptr;
}
```
AFTER:
```
template<typename T>
T perform_type_punning(std::ptrdiff_t offset)
{
T memptr;
std::memcpy(&memptr, &offset, sizeof(offset));
return memptr;
}
```
AFTER(C++20):
```
template<typename T>
T perform_type_punning(std::ptrdiff_t offset)
{
return std::bit_cast<T>(offset);
}
```
![]()
_______________________________________________
llvm-bugs mailing list
llvm-bugs@lists.llvm.org
https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-bugs
