[Bug tree-optimization/103332] New: Spurious -Wstringop-overflow warnings in libstdc++ tests

[Bug tree-optimization/103332] New: Spurious -Wstringop-overflow warnings in libstdc++ tests

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103332

            Bug ID: 103332
           Summary: Spurious -Wstringop-overflow warnings in libstdc++
                    tests
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Keywords: diagnostic
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: redi at gcc dot gnu.org
            Blocks: 88443
  Target Milestone: ---

In the $objdir/$target/libstdc++-v3/testsuite dir, running:

make check
RUNTESTFLAGS="conformance.exp=21_strings/basic_string/operators/char/1.cc
--target_board=unix/-D_GLIBCXX_DEBUG"

Results in:

In file included from
/home/jwakely/build/powerpc64le-unknown-linux-gnu/libstdc++-v3/include/string:40,^M
                 from
/home/jwakely/src/gcc/libstdc++-v3/testsuite/21_strings/basic_string/operators/char/1.cc:22:^M
In static member function 'static std::char_traits<char>::char_type*
std::char_traits<char>::copy(std::char_traits<char>::char_type*, const
std::char_traits<char>::char_type*, std::size_t)',^M
    inlined from 'std::__cxx11::basic_string<_CharT, _Traits,
_Alloc>::basic_string(std::__cxx11::basic_string<_CharT, _Traits, _Alloc>&&)
[with _CharT = char; _Traits = std::char_traits<char>; _Alloc =
std::allocator<char>]' at
/home/jwakely/build/powerpc64le-unknown-linux-gnu/libstdc++-v3/include/bits/basic_string.h:675,^M
    inlined from 'std::__cxx11::basic_string<_CharT, _Traits, _Allocator>
std::operator+(std::__cxx11::basic_string<_CharT, _Traits, _Allocator>&&, const
_CharT*) [with _CharT = char; _Traits = std::char_traits<char>; _Alloc =
std::allocator<char>]' at
/home/jwakely/build/powerpc64le-unknown-linux-gnu/libstdc++-v3/include/bits/basic_string.h:3552,^M
    inlined from 'int test01()' at
/home/jwakely/src/gcc/libstdc++-v3/testsuite/21_strings/basic_string/operators/char/1.cc:34:^M
/home/jwakely/build/powerpc64le-unknown-linux-gnu/libstdc++-v3/include/bits/char_traits.h:423:
warning: 'void* __builtin_memcpy(void*, const void*, long unsigned int)'
writing 17 bytes into a region of size 16 overflows the destination
[-Wstringop-overflow=]^M
/home/jwakely/src/gcc/libstdc++-v3/testsuite/21_strings/basic_string/operators/char/1.cc:
In function 'int test01()':^M
/home/jwakely/src/gcc/libstdc++-v3/testsuite/21_strings/basic_string/operators/char/1.cc:34:
note: at offset 16 into destination object '<anonymous>' of size 32^M
FAIL: 21_strings/basic_string/operators/char/1.cc (test for excess errors)
Excess errors:
/home/jwakely/build/powerpc64le-unknown-linux-gnu/libstdc++-v3/include/bits/char_traits.h:423:
warning: 'void* __builtin_memcpy(void*, const void*, long unsigned int)'
writing 17 bytes into a region of size 16 overflows the destination
[-Wstringop-overflow=]


And:

make check
RUNTESTFLAGS="conformance.exp=21_strings/basic_string/capacity/char/1.cc
--target_board=unix/-std=gnu++20"

results in:

In file included from
/home/jwakely/build/powerpc64le-unknown-linux-gnu/libstdc++-v3/include/string:40,^M
                 from
/home/jwakely/src/gcc/libstdc++-v3/testsuite/21_strings/basic_string/capacity/char/1.cc:22:^M
In static member function 'static constexpr std::char_traits<char>::char_type*
std::char_traits<char>::copy(std::char_traits<char>::char_type*, const
std::char_traits<char>::char_type*, std::size_t)',^M
    inlined from 'static constexpr void std::__cxx11::basic_string<_CharT,
_Traits, _Alloc>::_S_copy(_CharT*, const _CharT*,
std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::size_type) [with _CharT =
char; _Traits = std::char_traits<char>; _Alloc = std::allocator<char>]' at
/home/jwakely/build/powerpc64le-unknown-linux-gnu/libstdc++-v3/include/bits/basic_string.h:423,^M
    inlined from 'static constexpr void std::__cxx11::basic_string<_CharT,
_Traits, _Alloc>::_S_copy(_CharT*, const _CharT*,
std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::size_type) [with _CharT =
char; _Traits = std::char_traits<char>; _Alloc = std::allocator<char>]' at
/home/jwakely/build/powerpc64le-unknown-linux-gnu/libstdc++-v3/include/bits/basic_string.h:418,^M
    inlined from 'constexpr std::__cxx11::basic_string<_CharT, _Traits,
_Allocator>& std::__cxx11::basic_string<_CharT, _Traits,
_Alloc>::_M_append(const _CharT*, std::__cxx11::basic_string<_CharT, _Traits,
_Alloc>::size_type) [with _CharT = char; _Traits = std::char_traits<char>;
_Alloc = std::allocator<char>]' at
/home/jwakely/build/powerpc64le-unknown-linux-gnu/libstdc++-v3/include/bits/basic_string.tcc:417,^M
    inlined from 'constexpr std::__cxx11::basic_string<_CharT, _Traits,
_Alloc>& std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::append(const
std::__cxx11::basic_string<_CharT, _Traits, _Alloc>&) [with _CharT = char;
_Traits = std::char_traits<char>; _Alloc = std::allocator<char>]' at
/home/jwakely/build/powerpc64le-unknown-linux-gnu/libstdc++-v3/include/bits/basic_string.h:1385,^M
    inlined from 'constexpr std::__cxx11::basic_string<_CharT, _Traits,
_Allocator> std::operator+(const std::__cxx11::basic_string<_CharT, _Traits,
_Allocator>&, const std::__cxx11::basic_string<_CharT, _Traits, _Allocator>&)
[with _CharT = char; _Traits = std::char_traits<char>; _Alloc =
std::allocator<char>]' at
/home/jwakely/build/powerpc64le-unknown-linux-gnu/libstdc++-v3/include/bits/basic_string.h:3433,^M
    inlined from 'void test01()' at
/home/jwakely/src/gcc/libstdc++-v3/testsuite/21_strings/basic_string/capacity/char/1.cc:102:^M
/home/jwakely/build/powerpc64le-unknown-linux-gnu/libstdc++-v3/include/bits/char_traits.h:423:
warning: 'void* __builtin_memcpy(void*, const void*, long unsigned int)'
specified bound between 18446744073709551586 and 18446744073709551615 exceeds
maximum object size 9223372036854775807 [-Wstringop-overflow=]^M
FAIL: 21_strings/basic_string/capacity/char/1.cc (test for excess errors)
Excess errors:
/home/jwakely/build/powerpc64le-unknown-linux-gnu/libstdc++-v3/include/bits/char_traits.h:423:
warning: 'void* __builtin_memcpy(void*, const void*, long unsigned int)'
specified bound between 18446744073709551586 and 18446744073709551615 exceeds
maximum object size 9223372036854775807 [-Wstringop-overflow=]



And:

make check 
RUNTESTFLAGS"=conformance.exp=experimental/filesystem/path/factory/u8path-char8_t.cc
--target_board=unix/-std=gnu++20"


results in:

[...]
FAIL: experimental/filesystem/path/factory/u8path-char8_t.cc (test for excess
errors)
Excess errors:
/home/jwakely/build/powerpc64le-unknown-linux-gnu/libstdc++-v3/include/bits/char_traits.h:423:
warning: 'void* __builtin_memcpy(void*, const void*, long unsigned int)'
reading between 16 and 9223372036854775806 bytes from a region of size 10
[-Wstringop-overread]
/home/jwakely/build/powerpc64le-unknown-linux-gnu/libstdc++-v3/include/bits/char_traits.h:423:
warning: 'void* __builtin_memcpy(void*, const void*, long unsigned int)'
reading between 16 and 9223372036854775806 bytes from a region of size 10
[-Wstringop-overread]



These are all bogus, as far as I can tell. e.g. for the last one, we read 9
bytes from a string literal that is 10 bytes long (including the null) and
memcpy it into a buffer that is 16 bytes in size. That doesn't overflow.


Referenced Bugs:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88443
[Bug 88443] [meta-bug] bogus/missing -Wstringop-overflow warnings

[Bug tree-optimization/103332] Spurious -Wstringop-overflow warnings in libstdc++ tests

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103332

Martin Sebor <msebor at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |msebor at gcc dot gnu.org
           See Also|                            |https://gcc.gnu.org/bugzill
                   |                            |a/show_bug.cgi?id=102958

--- Comment #1 from Martin Sebor <msebor at gcc dot gnu.org> ---
Suspect at least some of these might be due to the same underlying problem as
pr102958.  I suppressed a subset of these warnings in
g:sy9a27acc30a34b7854db32eac562306cebac6fa1e.

[Bug tree-optimization/103332] Spurious -Wstringop-overflow warnings in libstdc++ tests

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103332

--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to Martin Sebor from comment #1)
> I suppressed a subset of these warnings in
> g:9a27acc30a34b7854db32eac562306cebac6fa1e.

Ah yes, I'll add the same again then, thanks.

[Bug tree-optimization/103332] Spurious -Wstringop-overflow warnings in libstdc++ tests

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103332

--- Comment #3 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Jonathan Wakely <redi@gcc.gnu.org>:

https://gcc.gnu.org/g:b8f2efaed02e8b03d215d74e42d3707761772f64

commit r12-5414-gb8f2efaed02e8b03d215d74e42d3707761772f64
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Fri Nov 19 18:13:10 2021 +0000

    libstdc++: Suppress -Wstringop warnings [PR103332]

    libstdc++-v3/ChangeLog:

            PR libstdc++/103332
            PR libstdc++/102958
            * testsuite/21_strings/basic_string/capacity/char/1.cc: Add
            -Wno-stringop-overflow.
            * testsuite/21_strings/basic_string/operators/char/1.cc:
            Likewise.
            * testsuite/experimental/filesystem/path/factory/u8path-char8_t.cc:
            Add -Wno-stringop-overread.

[Bug tree-optimization/103332] Spurious -Wstringop-overflow warnings in libstdc++ tests

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103332

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
     Ever confirmed|0                           |1
   Last reconfirmed|                            |2021-11-25
             Status|UNCONFIRMED                 |NEW

--- Comment #4 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
.

[Bug tree-optimization/103332] [12 Regression] Spurious -Wstringop-overflow on string concatenation in libstdc++ tests

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103332

Martin Sebor <msebor at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           See Also|                            |https://gcc.gnu.org/bugzill
                   |                            |a/show_bug.cgi?id=103534
            Summary|Spurious                    |[12 Regression] Spurious
                   |-Wstringop-overflow         |-Wstringop-overflow on
                   |warnings in libstdc++ tests |string concatenation in
                   |                            |libstdc++ tests
      Known to fail|                            |12.0

--- Comment #5 from Martin Sebor <msebor at gcc dot gnu.org> ---
The first warning is for the invalid memcpy() call below:

  struct string D.35215;
  ...
  <bb 3> [local count: 1073312331]:
  D.35215._M_string_length = 16;
  _62 = D.35215._M_dataplus._M_p;
  MEM[(char_type &)_62 + 16] = 0;
  D.35222 ={v} {CLOBBER};
  MEM[(struct _Alloc_hider *)&D.35222] ={v} {CLOBBER};
  MEM[(struct _Alloc_hider *)&D.35222]._M_p = &D.35222.D.28102._M_local_buf;
  if (&MEM <const char[16]> [(void *)&D.35215 + 16B] == _62)
    goto <bb 4>; [30.00%]
  else
    goto <bb 5>; [70.00%]

  <bb 4> [local count: 157390518]:
  __builtin_memcpy (&D.35222.D.28102._M_local_buf, &MEM <const char[16]> [(void
*)&D.35215 + 16B], 17);
  goto <bb 6>; [100.00%]

sizeof std::string::_M_local_buf is 16 but the call writes 17 bytes into it, so
the call is invalid.

I only see the warning at -O1 (and with -D_GLIBCXX_DEBUG).  It also goes away
if I force std::string::_M_mutate to be inlined.  _M_mutate allocates the
dynamic string so with it inlined GCC can determine that the local buffer is no
longer used and eliminate the invalid call.  So as in the other cases we have
seen recently, this false positive is due to some optimizer limitations caused
by the combination of -O1 and a decision to throttle inlining.  The second
warning is due to the same issue.  It too goes away with more aggressive
inlining (on x86_64 setting -finline-limit=200 avoids it).

[Bug tree-optimization/103332] [12 Regression] Spurious -Wstringop-overflow on string concatenation in libstdc++ tests

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103332

--- Comment #6 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Jonathan Wakely <redi@gcc.gnu.org>:

https://gcc.gnu.org/g:f8463b0e3ec2438b4cfb8c9a468d59761db2c8a0

commit r12-5874-gf8463b0e3ec2438b4cfb8c9a468d59761db2c8a0
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Thu Dec 2 13:19:41 2021 +0000

    libstdc++: Disable over-zealous warnings about std::string copies
[PR103332]

    These warnings are triggered by perfectly valid code using std::string.
    They're particularly bad when --enable-fully-dynamic-string is used,
    because even std::string().begin() will give a warning.

    Use pragmas to stop the troublesome warnings for copies done by
    std::char_traits.

    libstdc++-v3/ChangeLog:

            PR libstdc++/103332
            PR libstdc++/102958
            PR libstdc++/103483
            * include/bits/char_traits.h: Suppress stringop and array-bounds
            warnings.

[Bug tree-optimization/103332] [12 Regression] Spurious -Wstringop-overflow on string concatenation in libstdc++ tests

[jason at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103332

Jason Merrill <jason at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|---                         |DUPLICATE
                 CC|                            |jason at gcc dot gnu.org

--- Comment #7 from Jason Merrill <jason at gcc dot gnu.org> ---
Same append issue.

*** This bug has been marked as a duplicate of bug 103534 ***