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

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

[cfy1990 at gmail dot com]

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;
}

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

[cfy1990 at gmail dot com]

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

--- Comment #1 from cfy1990 at gmail dot com ---
When compile without -O2, g++ will generate "'v3' may be used uninitialized"
warning.
code link: https://godbolt.org/z/r3sY4srx9

[Bug tree-optimization/105646] g++ does not raise "xxx may be used uninitialized" warning on dead code when optimizing

[cvs-commit at gcc dot gnu.org]

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

--- Comment #3 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Richard Biener <rguenth@gcc.gnu.org>:

https://gcc.gnu.org/g:a1cd4d52d6ef90b977fb2d80c1cf17f3efa5b01d

commit r13-2926-ga1cd4d52d6ef90b977fb2d80c1cf17f3efa5b01d
Author: Richard Biener <rguenther@suse.de>
Date:   Fri Aug 19 15:11:14 2022 +0200

    tree-optimization/105646 - re-interpret always executed in uninit diag

    The following fixes PR105646, not diagnosing

    int f1();
    int f3(){
        auto const & a = f1();
        bool v3{v3};
        return a;
    }

    with optimization because the early uninit diagnostic pass only
    diagnoses always executed cases.  The patch does this by
    re-interpreting what always executed means and choosing to
    ignore exceptional and abnormal control flow for this.  At the
    same time it improves things as suggested in a comment - when
    the value-numbering run done without optimizing figures there's
    a fallthru path, consider blocks on it as always executed.

            PR tree-optimization/105646
            * tree-ssa-uninit.cc (warn_uninitialized_vars): Pre-compute
            the set of fallthru reachable blocks from function entry
            and use that to determine wlims.always_executed.

            * g++.dg/uninit-pr105646.C: New testcase.

[Bug tree-optimization/105646] g++ does not raise "xxx may be used uninitialized" warning on dead code when optimizing

[rguenth at gcc dot gnu.org]

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

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
      Known to work|                            |13.0
         Resolution|---                         |FIXED

--- Comment #4 from Richard Biener <rguenth at gcc dot gnu.org> ---
Fixed on trunk.

[Bug tree-optimization/105646] g++ does not raise "xxx may be used uninitialized" warning on dead code when optimizing

[pinskia at gcc dot gnu.org]

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

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |13.0