[Bug c++/112546] New: -Wmaybe-uninitialized and -Wuninitialized does not detect usage of uninitilazed value in a lambda

[federico at kircheis dot it]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112546

            Bug ID: 112546
           Summary: -Wmaybe-uninitialized and -Wuninitialized does not
                    detect usage of uninitilazed value in a lambda
           Product: gcc
           Version: 13.2.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: federico at kircheis dot it
  Target Milestone: ---

I noticed the issue when comparing this three equivalent bar functions:


----
struct data{
        int i;
};
data foo();
void bar(const data& d);

void bar1(){
    data d = [&]{bar(d); return foo();}();
}

void bar2(){
    data d = (bar(d), void(), foo());
}


void bar3(){
    data d;
    bar(d);
    d = foo();
}
----


example on godbolt: https://godbolt.org/z/Wxj6rbKb9
With "-Wmaybe-uninitialized", GCC detects in bar2 and bar3 that d is possible
used inside bar without being initialized, but it fails to do so when using a
lambda.

In fact, I noticed that it fails to report (with "-Wuninitialized") even when
the value is used directly in the lambda:


----
void bar4(){
    data d = [&]{ ++d.i; bar(d); return foo();}();
}
----