hanickadot wrote:
I was also implementing this and run into an issue, so I looked into your
implementation and you have exactly same issue as I do, following code will
fail:
```c++
namespace std {
template <typename T> consteval bool is_within_lifetime(const T * ptr) noexcept
{
return __builtin_is_within_lifetime(ptr);
}
}
constexpr bool test_union(int * i) { // <-- note the constexpr here
return std::is_within_lifetime(i);
}
static_assert([] consteval {
union { int i; char c; } u = {.i = 10};
return test_union(&u.i);
}());
```
with error:
```
./builtin-is-within-lifetime-call.cpp:8:10: error: call to consteval function
'std::is_within_lifetime<int>' is not a constant expression
8 | return std::is_within_lifetime(i);
| ^
./builtin-is-within-lifetime-call.cpp:8:34: note: function parameter 'i' with
unknown value cannot be used in a constant expression
8 | return std::is_within_lifetime(i);
| ^
./builtin-is-within-lifetime-call.cpp:7:33: note: declared here
7 | constexpr bool test_union(int * i) { // <-- note the constexpr here
| ^
1 error generated.
```
https://github.com/llvm/llvm-project/pull/91895
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