https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107744
Bug ID: 107744
Summary: Error in constant evaluation of dynamic_cast
Product: gcc
Version: 12.2.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: fchelnokov at gmail dot com
Target Milestone: ---
The following program
struct A {
constexpr A();
virtual void f() {}
bool x;
};
struct B : A {};
constexpr A::A() {
x = dynamic_cast<B*>(this);
}
constexpr bool b = B{}.x;
is accepted by Clang and MSVC, but GCC prints vague error:
<source>:12:24: in 'constexpr' expansion of 'B()'
<source>:7:8: in 'constexpr' expansion of '((B*)this)->B::<anonymous>.A::A()'
<source>:12:24: error: '((&<anonymous>.B::<anonymous>) != 0)' is not a constant
expression
12 | constexpr bool b = B{}.x;
Online demo: https://godbolt.org/z/1xdq68aaM
