https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70796
Matthijs van Duin <matthijsvanduin at gmail dot com> changed:
What |Removed |Added
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CC| |matthijsvanduin at gmail dot
com
--- Comment #3 from Matthijs van Duin <matthijsvanduin at gmail dot com> ---
This specifically appears to happen when the constructor has parameters of
trivially copyable non-reference types, e.g. this fails:
#include <assert.h>
struct IntWrap {
int x = 0;
IntWrap &operator ++() { ++x; return *this; }
};
struct Pair {
IntWrap first, second;
Pair( IntWrap x, IntWrap y ) : first{ x }, second{ y } { }
};
int main() {
IntWrap i;
Pair p{ ++i, ++i };
assert( p.first.x == 1 && p.second.x == 2 ); // FAIL (p.first.x is 2)
}
but adding a destructor to IntWrap suffices to make it pass.
Interestingly, when using simple ints there also appear to be very narrow
constraints on the initializer arguments to trigger the bug:
#include <assert.h>
struct IntPair {
int first, second;
IntPair( int x, int y ) : first{ x }, second{ y } { }
};
void testcase_fail() {
int i = 0;
IntPair p{ ++i, ++i };
assert( p.first == 1 && p.second == 2 ); // FAIL (p.first is 2)
}
void testcase_ok_1() {
int i = 0;
IntPair p{ ++i, ++i };
assert( p.first == 1 && p.second == 2 ); // ok
int &j = i;
IntPair q{ ++j, ++j };
assert( q.first == 3 && q.second == 4 ); // ok
}
void testcase_ok_2() {
int i = 0;
IntPair p{ (int &)++i, (int &)++i };
assert( p.first == 1 && p.second == 2 ); // ok
}
int main() {
testcase_ok_1();
testcase_ok_2();
testcase_fail();
}
even though the analogous testcases for IntWrap all fail.
Related:
bug 51253 (was supposed to have fixed this but evidently missed some cases)
bug 65866 (incorrect -Wsequence-point diagnostic still being emitted)
bug 70792 (dup of bug 65866 but discussion in comments covered this case)
