[libcxx-commits] [libcxx] [libcxx] Align allocation to match `__set_long_cap` and `__get_long_cap` (PR #90292)

[Vitaly Buka via libcxx-commits]

================
@@ -1876,6 +1876,7 @@ private:
   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 void __set_long_cap(size_type __s) _NOEXCEPT {
     __r_.first().__l.__cap_     = __s / __endian_factor;
     __r_.first().__l.__is_long_ = true;
+    _LIBCPP_ASSERT_INTERNAL(__s == __get_long_cap(), "Size must be __endian_factor aligned.");
----------------
vitalybuka wrote:

I see:

https://github.com/llvm/llvm-project/actions/runs/8899718744/job/24441331959?pr=90645

Also my local run if we apply only #90645
```
gdb runtimes/runtimes-bins/test/std/strings/basic.string/string.modifiers/string_replace/Output/size_size_pointer_size.pass.cpp.dir/t.tmp.exe
```

```
#0  __pthread_kill_implementation (threadid=<optimized out>, signo=6, no_tid=no_tid at entry=0) at ./nptl/pthread_kill.c:44
#1  0x00007ffff7b691cf in __pthread_kill_internal (signo=<optimized out>, threadid=<optimized out>) at ./nptl/pthread_kill.c:89
#2  __GI___pthread_kill (threadid=<optimized out>, signo=<optimized out>) at ./nptl/pthread_kill.c:89
#3  0x00007ffff7cb3e90 in ?? () from /lib/x86_64-linux-gnu/libc.so.6
#4  0x00007ffff7b054b2 in __GI_abort () at ./stdlib/abort.c:79
#5  0x00007ffff7f44bce in std::__1::__libcpp_verbose_abort (format=0x7ffff7e9c1f8 "%s")
    at /usr/local/google/home/vitalybuka/src/llvm.git/llvm-project/libcxx/src/verbose_abort.cpp:74
#6  0x00007ffff7f2da14 in std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >::__set_long_cap[abi:de190000](unsigned long) (this=0x7fffffffc7b0, __s=25) at include/c++/v1/string:1879
#7  0x00007ffff7f3ab96 in std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >::__init (this=0x7fffffffc7b0, 
    __s=0x5555555e638d "1234567890123456789bcde", __sz=23) at include/c++/v1/string:2233
#8  0x0000555555584334 in std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >::basic_string[abi:de190000]<0>
    ()
#9  0x0000555555557441 in bool test0<std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > >() ()
#10 0x00005555555552d9 in void test<std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > >() ()
#11 0x00005555555552bb in main ()
```

1. __init(const value_type* __s, size_type __sz = 23)
2. __recommend(23) returns 24, because 23 is `__min_cap`
3. then as in the description we allocate 25, but store  `25 / 2`
4. and next time we delete 24

https://github.com/llvm/llvm-project/pull/90292