[llvm-bugs] [Bug 49345] New: MemorySanitizer: use-of-uninitialized-value in std::ostream::__put_character_sequence

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=49345

            Bug ID: 49345
           Summary: MemorySanitizer: use-of-uninitialized-value in
                    std::ostream::__put_character_sequence
           Product: libc++
           Version: 11.0
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: All Bugs
          Assignee: unassignedclangbugs at nondot.org
          Reporter: nok.raven at gmail.com
                CC: llvm-bugs at lists.llvm.org, mclow.lists at gmail.com

#include <iostream>

int main() {
   std::cout << "hmm";
}


$ clang++ z.cpp -g -stdlib=libc++ -fsanitize=memory && ./a.out
==3636==WARNING: MemorySanitizer: use-of-uninitialized-value
    #0 0x499fd4 in std::__1::basic_ostream<char, std::__1::char_traits<char> >&
std::__1::__put_character_sequence<char, std::__1::char_traits<char>
>(std::__1::basic_ostream<char, std::__1::char_traits<char> >&, char const*,
unsigned long) /usr/lib/llvm-11/bin/../include/c++/v1/ostream:727:13
    #1 0x499eb6 in std::__1::basic_ostream<char, std::__1::char_traits<char> >&
std::__1::operator<<<std::__1::char_traits<char>
>(std::__1::basic_ostream<char, std::__1::char_traits<char> >&, char const*)
/usr/lib/llvm-11/bin/../include/c++/v1/ostream:869:12
    #2 0x499db6 in main /home/user/z.cpp:4:14
    #3 0x7f3924d89cb1 in __libc_start_main csu/../csu/libc-start.c:314:16
    #4 0x41d32d in _start (/home/user/a.out+0x41d32d)

SUMMARY: MemorySanitizer: use-of-uninitialized-value
/usr/lib/llvm-11/bin/../include/c++/v1/ostream:727:13 in
std::__1::basic_ostream<char, std::__1::char_traits<char> >&
std::__1::__put_character_sequence<char, std::__1::char_traits<char>
>(std::__1::basic_ostream<char, std::__1::char_traits<char> >&, char const*,
unsigned long)
Exiting

>        typename basic_ostream<_CharT, _Traits>::sentry __s(__os);
>        if (__s)
>            ^

https://godbolt.org/z/o3f6z6

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