[Bug c++/105646] New: g++ does not raise xxx is used uninitialized warning under some conditions

[cfy1990 at gmail dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105646

            Bug ID: 105646
           Summary: g++ does not raise xxx is used uninitialized warning
                    under some conditions
           Product: gcc
           Version: 12.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: cfy1990 at gmail dot com
  Target Milestone: ---

g++ version: g++ (Compiler-Explorer-Build-gcc--binutils-2.38) 12.1.0
Code link: https://godbolt.org/z/5MansKa5c
Compile arguments: -std=c++11  -Wextra -Wall -O2

Code:

int f1();
int f2(){
    bool v2{v2}; // used uninitialized warning
    auto const & a = f1();
    return a;
}
int f3(){
    auto const & a = f1();
    bool v3{v3}; // no warning in g++, got uninitialized warning in clang
    return a;
}