https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90852
Bug ID: 90852
Summary: A recurring bug: Constant expressions support
reinterpret_cast
Product: gcc
Version: 10.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: zhonghao at pku dot org.cn
Target Milestone: ---
A previous bug report (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=49171)
contains two samples:
//---
constexpr const char* c = reinterpret_cast<const char*>(0x123);
//---
//----------------
struct X {
X* operator&();
};
X x[2];
const bool p = (reinterpret_cast<X*>(&reinterpret_cast<char&>(x[1]))
- reinterpret_cast<X*>(&reinterpret_cast<char&>(x[0]))) == sizeof(X);
enum E { e = p }; // e should have a value equal to 1
//----------------
After some discussions, programmers agree that the first sample shall be
reject, but the second sample has its value. gcc 7.2 accepts the code. However,
gcc 10.0.0 rejects it:
source>:10:14: error: the value of 'p' is not usable in a constant expression
10 | enum E { e = p }; // e should have a value equal to 1
| ^
<source>:7:12: note: 'p' was not initialized with a constant expression
7 | const bool p = (reinterpret_cast<X*>(&reinterpret_cast<char&>(x[1]))
| ^
<source>:10:14: error: the value of 'p' is not usable in a constant expression
10 | enum E { e = p }; // e should have a value equal to 1
| ^
<source>:7:12: note: 'p' was not initialized with a constant expression
7 | const bool p = (reinterpret_cast<X*>(&reinterpret_cast<char&>(x[1]))
| ^
<source>:10:14: error: enumerator value for 'e' is not an integer constant
10 | enum E { e = p }; // e should have a value equal to 1
| ^
Compiler returned: 1
