https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100047
Bug ID: 100047
Summary: False -Wmaybe-uninitialized on one var depending on
type of other var
Product: gcc
Version: 11.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: gccbugbjorn at fahller dot se
Target Milestone: ---
With the following C++17 code, there's a warning that m_size can be used
uninitialized if m_ptr is a std::unique_ptr<>, but not if it is a raw pointer.
This only happens when some optimization is enabled. -Og is enough. The bug
also applies to gcc-10, gcc-9 and gcc-8 (have not checked older versions).
#include <cstdint>
#include <cstdlib>
#include <optional>
#include <memory>
#include <string>
#if EXPOSE_BUG
using buffer_ptr = std::unique_ptr<uint8_t>;
#else
using buffer_ptr = const uint8_t*;
#endif
const uint8_t* get(const std::unique_ptr<uint8_t>& ptr)
{
return ptr.get();
}
const uint8_t* get(const uint8_t* ptr)
{
return ptr;
}
class packet_buffer
{
public:
using const_iterator = const uint8_t*;
packet_buffer() : m_ptr(nullptr), m_size(0) {}
packet_buffer(buffer_ptr ptr, uint16_t size)
: m_ptr(std::move(ptr)), m_size(size)
{
}
size_t size() const { return m_size; } // <- here
const uint8_t* data() const { return get(m_ptr); }
const_iterator begin() const { return data(); }
const_iterator end() const { return data() + size(); }
private:
buffer_ptr m_ptr;
uint16_t m_size = 0;
};
std::string func()
{
auto f =
[](std::optional<packet_buffer> result) {
auto&& b = result.value();
return std::string(b.begin(), b.end());
};
return f(std::nullopt);
}
Godbolt link:
https://godbolt.org/z/63z8qzcxv
