https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110642
Bug ID: 110642
Summary: Undefined behavior in same constant expression is
found not always
Product: gcc
Version: 13.1.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: fchelnokov at gmail dot com
Target Milestone: ---
This lambda
auto f = [](int i) {
const auto y = i;
return [&] () {
return y;
};
};
returns another lambda that makes undefined behavior: it accesses a stack
variable (y) after the end of its life.
And it is successfully caught during constant expression evaluation by GCC and
other compilers, if verified like this:
constexpr auto g = f(3)();
static_assert( f(3)() == 3 );
Online demo: https://gcc.godbolt.org/z/3Y4cGMG15
But if one changes the order of lines:
static_assert( f(3)() == 3 );
constexpr auto g = f(3)();
then GCC stops detecting undefined behavior. Online demo:
https://gcc.godbolt.org/z/dojhKasPs
Could you please review why this happens?
