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From: "soren.soe at gonsoe dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/99689] New: Initialized local variable becomes
 uninitialized after use
Date: Sat, 20 Mar 2021 20:11:11 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D99689

            Bug ID: 99689
           Summary: Initialized local variable becomes uninitialized after
                    use
           Product: gcc
           Version: 9.3.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: soren.soe at gonsoe dot com
  Target Milestone: ---

Created attachment 50439
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=3D50439&action=3Dedit
preprocessed file (*.i*) that triggers the bug

% g++ -v
Using built-in specs.
COLLECT_GCC=3Dg++
COLLECT_LTO_WRAPPER=3D/usr/lib/gcc/aarch64-linux-gnu/9/lto-wrapper
Target: aarch64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion=3D'Ubuntu
9.3.0-17ubuntu1~20.04' --with-bugurl=3Dfile:///usr/share/doc/gcc-9/README.B=
ugs
--enable-languages=3Dc,ada,c++,go,d,fortran,objc,obj-c++,gm2 --prefix=3D/usr
--with-gcc-major-version-only --program-suffix=3D-9
--program-prefix=3Daarch64-linux-gnu- --enable-shared --enable-linker-build=
-id
--libexecdir=3D/usr/lib --without-included-gettext --enable-threads=3Dposix
--libdir=3D/usr/lib --enable-nls --enable-clocale=3Dgnu --enable-libstdcxx-=
debug
--enable-libstdcxx-time=3Dyes --with-default-libstdcxx-abi=3Dnew
--enable-gnu-unique-object --disable-libquadmath --disable-libquadmath-supp=
ort
--enable-plugin --enable-default-pie --with-system-zlib
--with-target-system-zlib=3Dauto --enable-objc-gc=3Dauto --enable-multiarch
--enable-fix-cortex-a53-843419 --disable-werror --enable-checking=3Drelease
--build=3Daarch64-linux-gnu --host=3Daarch64-linux-gnu --target=3Daarch64-l=
inux-gnu
Thread model: posix
gcc version 9.3.0 (Ubuntu 9.3.0-17ubuntu1~20.04)=20

% cat bug.cpp
#include <cassert>
#include <string>
#include <utility>
#include <vector>

using vec =3D std::vector<std::pair<std::string, std::string>>;

void
bad()
{
  vec v;
  v.emplace_back("abc", "def");
  v.emplace_back("abc", "def");
  v.emplace_back("abc", "def");
  v.emplace_back("abc", "def");
  v.emplace_back("abc", "def");

  unsigned int m =3D 0;
  for (auto& p : v)
    m =3D std::max<unsigned int>(m, p.first.length());

  assert(m =3D=3D 3);
}

int main()
{
  bad();
  return 0;
}


% g++ -Wall -Wextra -O3 -std=3Dc++14 bug.cpp=20
% ./a.out=20
a.out: bug.cpp:79: void bad(): Assertion `m =3D=3D 3' failed.
Aborted (core dumped)=