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From: "gnu at gonsoe dot com" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug middle-end/99689] Initialized local variable becomes
 uninitialized after use
Date: Mon, 22 Mar 2021 19:42:26 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D99689

Soren Soe <gnu at gonsoe dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |gnu at gonsoe dot com

--- Comment #5 from Soren Soe <gnu at gonsoe dot com> ---
I've tried all options.  Fails only when compiled with -O3.

I looked at assembler code on https://godbolt.org, and it appears that with=
 ARM
gcc9.3 the unsigned int variable is not initialized.  The assembler code is
very different if unsigned int is replaced with size_t, or when using -O2, =
and
appears to show a variable initialized to 0.

void
good()
{
  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");

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

  assert(m=3D=3D3);
}

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=3D3);
}=