std::wstring::find() broken in g++?

Question

What's wrong with this program:

#include <string>
int main()
{
    std::wstring s = L"12345";
    s.find(L"x");
    return 0;
}

If nothing is wrong, why does Valgrind complain:

$ g++ -g main.cpp 
$ valgrind ./a.out 
==9301== Memcheck, a memory error detector
==9301== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et al.
==9301== Using Valgrind-3.13.0 and LibVEX; rerun with -h for copyright info
==9301== Command: ./a.out
==9301== 
==9301== Conditional jump or move depends on uninitialised value(s)
==9301==    at 0x54AD3C1: __wmemchr_sse2 (memchr.S:254)
==9301==    by 0x4F7667A: std::__cxx11::basic_string<wchar_t, std::char_traits<wchar_t>, std::allocator<wchar_t> >::find(wchar_t const*, unsigned long, unsigned long) const (in /usr/lib/x86_64-linux-gnu/libstdc++.so.6.0.25)
==9301==    by 0x108A28: main (main.cpp:5)
==9301== 
==9301== 
==9301== HEAP SUMMARY:
==9301==     in use at exit: 0 bytes in 0 blocks
==9301==   total heap usage: 2 allocs, 2 frees, 72,728 bytes allocated
==9301== 
==9301== All heap blocks were freed -- no leaks are possible
==9301== 
==9301== For counts of detected and suppressed errors, rerun with: -v
==9301== Use --track-origins=yes to see where uninitialised values come from
==9301== ERROR SUMMARY: 1 errors from 1 contexts (suppressed: 0 from 0)

Note that when I reduce the size of the string by one character:

#include <string>
int main()
{
    std::wstring s = L"1234"; // string is shorter by one character
    s.find(L"x");
    return 0;
}

or when I search for a character that is in the string:

#include <string>
int main()
{
    std::wstring s = L"12345";
    s.find(L"5"); // '5' is in the string
    return 0;
}

or when I use std::string instead of std::wstring:

#include <string>
int main()
{
    std::string s = "12345"; // std::string instead of std::wstring
    s.find("x");
    return 0;
}

then Valgrind does not complain.

My environment:

$ uname -a
Linux dave-VirtualBox 4.15.0-101-generic #102-Ubuntu SMP Mon May 11 10:07:26 UTC 2020 x86_64 x86_64 x86_64 GNU/Linux
$ g++ --version
g++ (Ubuntu 7.5.0-3ubuntu1~18.04) 7.5.0
Copyright (C) 2017 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
$ valgrind --version 
valgrind-3.13.0

Answer 1

Probably a bug on valgrind side. I tested with g++ 10.2 and with valgrind 3.16, it worked without an error.