https://gcc.gnu.org/bugzilla/show_bug.cgi?id=117727
Bug ID: 117727
Summary: __builtin_bit_cast with target type nullptr_t
unimplemented
Product: gcc
Version: 15.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: tbaeder at redhat dot com
Target Milestone: ---
See this example code:
typedef __UINTPTR_TYPE__ uintptr_t;
constexpr uintptr_t A = __builtin_bit_cast(uintptr_t, nullptr);
static_assert(A == 0);
typedef decltype(nullptr) nullptr_t;
constexpr decltype(nullptr) N = __builtin_bit_cast(nullptr_t, (uintptr_t)12);
static_assert(N == nullptr);
The first bitcast works, but the second one doesn't:
array.cpp:30:52: sorry, unimplemented: ‘__builtin_bit_cast’ cannot be constant
evaluated because the argument cannot be interpreted
30 | constexpr decltype(nullptr) N = __builtin_bit_cast(nullptr_t,
(uintptr_t)12);
| ^~~~~~~~~
I think this should work similarly. I checked that using std::nullptr_t from
<cstddef> has the same problem.
