[llvm-dev] False positive #2, std::move warning on clang 9.0.1 --analyze

[Jan Engelhardt via llvm-dev]

clang --analyze emits a warning about invoking functions on moved objects
that should not be there.

If you call subfld.reset() directly, the warning goes away. This suggests
"reset" is hardcoded in the analyzer, and that it is only valid for the "first"
nesting level. Having reset inside rezet and calling rezet, and the warning
appears (as shown):


» cat y.cpp 
#include <utility>
template<typename T> struct object_ptr {
        // kind of like shared_ptr but (much)less for sake of testcase
        object_ptr() {}
        object_ptr(T *p) : m_ptr(p) {}
        object_ptr(object_ptr &&o) : m_ptr(o.m_ptr) { o.m_ptr = nullptr; }
        object_ptr &operator=(object_ptr &&o) { return *this; }
        ~object_ptr() { delete m_ptr; }
        T *operator->() const { return m_ptr; }
        void reset() { m_ptr = nullptr; }
        void rezet() { reset(); }

        T *m_ptr = nullptr;
};
struct folder {
        void create_folder(folder **f);
};
void func()
{
        object_ptr<folder> fld{new folder}, subfld;
        fld = std::move(subfld);
        subfld.rezet();
}

» clang++ --analyze /dev/shm/y.cpp -v
clang version 9.0.1 
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /usr/bin
Found candidate GCC installation: /usr/bin/../lib64/gcc/x86_64-suse-linux/10
Found candidate GCC installation: /usr/bin/../lib64/gcc/x86_64-suse-linux/9
Found candidate GCC installation: /usr/lib64/gcc/x86_64-suse-linux/10
Found candidate GCC installation: /usr/lib64/gcc/x86_64-suse-linux/9
Selected GCC installation: /usr/bin/../lib64/gcc/x86_64-suse-linux/10
Candidate multilib: .;@m64
Selected multilib: .;@m64
 "/usr/bin/clang-9.0.1" -cc1 -triple x86_64-unknown-linux-gnu -analyze -disable-free -disable-llvm-verifier -discard-value-names -main-file-name y.cpp -analyzer-store=region -analyzer-opt-analyze-nested-blocks -analyzer-checker=core -analyzer-checker=apiModeling -analyzer-checker=unix -analyzer-checker=deadcode -analyzer-checker=cplusplus -analyzer-checker=security.insecureAPI.UncheckedReturn -analyzer-checker=security.insecureAPI.getpw -analyzer-checker=security.insecureAPI.gets -analyzer-checker=security.insecureAPI.mktemp -analyzer-checker=security.insecureAPI.mkstemp -analyzer-checker=security.insecureAPI.vfork -analyzer-checker=nullability.NullPassedToNonnull -analyzer-checker=nullability.NullReturnedFromNonnull -analyzer-output plist -w -mrelocation-model static -mthread-model posix -mdisable-fp-elim -fmath-errno -masm-verbose -mconstructor-aliases -munwind-tables -fuse-init-array -target-cpu x86-64 -dwarf-column-info -debugger-tuning=gdb -v -resource-dir /usr/lib64/clang/9.0.1
  -internal-isystem /usr/bin/../lib64/gcc/x86_64-suse-linux/10/../../../../include/c++/10 -internal-isystem /usr/bin/../lib64/gcc/x86_64-suse-linux/10/../../../../include/c++/10/x86_64-suse-linux -internal-isystem /usr/bin/../lib64/gcc/x86_64-suse-linux/10/../../../../include/c++/10/backward -internal-isystem /usr/local/include -internal-isystem /usr/lib64/clang/9.0.1/include -internal-externc-isystem /include -internal-externc-isystem /usr/include -fdeprecated-macro -fdebug-compilation-dir /dev/shm -ferror-limit 19 -fmessage-length 0 -fobjc-runtime=gcc -fcxx-exceptions -fexceptions -fdiagnostics-show-option -fcolor-diagnostics -faddrsig -o y.plist -x c++ /dev/shm/y.cpp
clang -cc1 version 9.0.1 based upon LLVM 9.0.1 default target x86_64-unknown-linux-gnu
ignoring nonexistent directory "/include"
#include "..." search starts here:
#include <...> search starts here:
 /usr/bin/../lib64/gcc/x86_64-suse-linux/10/../../../../include/c++/10
 /usr/bin/../lib64/gcc/x86_64-suse-linux/10/../../../../include/c++/10/x86_64-suse-linux
 /usr/bin/../lib64/gcc/x86_64-suse-linux/10/../../../../include/c++/10/backward
 /usr/local/include
 /usr/lib64/clang/9.0.1/include
 /usr/include
End of search list.
y.cpp:22:2: warning: Method called on moved-from object 'subfld'
        subfld.rezet();
        ^~~~~~~~~~~~~~
1 warning generated.