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From: "carlosgalvezp at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/106901] False positive -Warray-bounds with -O2 or higher?
Date: Sun, 11 Sep 2022 08:31:37 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D106901

--- Comment #5 from Carlos Galvez <carlosgalvezp at gmail dot com> ---
I also would like to understand why the warning is not triggered if the fir=
st
"if (size < expected_size)" is removed.=20

https://godbolt.org/z/7vqPxhsqo

The possibility of executing the loop and do out-of-bounds still exists, ri=
ght?
So why is the compiler warning in one case and not other?

Similarly, a regular for-loop with "size" known at runtime is equally risky,
yet the compiler is not flagging it:

bool bar(std::array<int, 5> const& vec,
         std::size_t const size)
{
    for (std::size_t i{0}; i < size; ++i)
    {
        if (vec[i] !=3D 0)
        {
            return false;
        }
    }
    return true;
}

https://godbolt.org/z/6c64MEY7d

Personally, I think this warning should only warn about 100% confirmed OOB
cases, and put the "maybe" cases in a separate flag. All respectable projec=
ts
have as minimum "-Wall -Werror" in their compiler flags, to detect problems
that do exist, not that "might" exist. This can lead to quite a few false
positives, leading to people either disabling the warning altogether (which=
 is
pretty bad!) or polluting the code with inline pragmas (disallowed by some
coding guidelines).=