[Bug c++/84587] New: [8 Regression] Local variable initializer goes out of scope since r247793

[marxin at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84587

            Bug ID: 84587
           Summary: [8 Regression] Local variable initializer goes out of
                    scope since r247793
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: marxin at gcc dot gnu.org
                CC: jakub at gcc dot gnu.org, jason at gcc dot gnu.org,
                    mpolacek at gcc dot gnu.org
  Target Milestone: ---

Starting from the mentioned revision:

$ cat /tmp/snippet.cc
#include <cstdlib>
#include <initializer_list>

template<typename T>
class ArrayView
{
public:
    using size_t = std::size_t;

    constexpr ArrayView(const std::initializer_list<T>& v)
        : m_pointer(v.begin()), m_size(v.size()) {}


    [[gnu::always_inline]]
    constexpr T& operator[](size_t n) const { return *(m_pointer + n); }

private:
    T* m_pointer;
    size_t m_size;
};

int main()
{
  ArrayView<const char> a = {'a', 'b', 'c'};

  return a[0];
}

$ g++ -g /tmp/snippet.cc -fsanitize=address -std=c++11 && ./a.out 
=================================================================
==3792==ERROR: AddressSanitizer: stack-use-after-scope on address
0x7fffffffda70 at pc 0x000000400af9 bp 0x7fffffffda30 sp 0x7fffffffda28
READ of size 1 at 0x7fffffffda70 thread T0
    #0 0x400af8 in main /tmp/snippet.cc:26
    #1 0x7ffff6186f49 in __libc_start_main (/lib64/libc.so.6+0x20f49)
    #2 0x4007d9 in _start (/home/marxin/Programming/testcases/a.out+0x4007d9)

Address 0x7fffffffda70 is located in stack of thread T0 at offset 32 in frame
    #0 0x400895 in main /tmp/snippet.cc:23

  This frame has 3 object(s):
    [32, 35) '<unknown>' <== Memory access at offset 32 is inside this variable
    [96, 112) 'a'
    [160, 176) '<unknown>'
HINT: this may be a false positive if your program uses some custom stack
unwind mechanism or swapcontext
      (longjmp and C++ exceptions *are* supported)
SUMMARY: AddressSanitizer: stack-use-after-scope /tmp/snippet.cc:26 in main
Shadow bytes around the buggy address:
  0x10007fff7af0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x10007fff7b00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x10007fff7b10: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x10007fff7b20: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x10007fff7b30: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
=>0x10007fff7b40: 00 00 00 00 00 00 00 00 00 00 f1 f1 f1 f1[f8]f2
  0x10007fff7b50: f2 f2 f2 f2 f2 f2 00 00 f2 f2 f2 f2 f2 f2 f8 f8
  0x10007fff7b60: f2 f2 f3 f3 f3 f3 00 00 00 00 00 00 00 00 00 00
  0x10007fff7b70: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x10007fff7b80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x10007fff7b90: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
Shadow byte legend (one shadow byte represents 8 application bytes):
  Addressable:           00
  Partially addressable: 01 02 03 04 05 06 07 
  Heap left redzone:       fa
  Freed heap region:       fd
  Stack left redzone:      f1
  Stack mid redzone:       f2
  Stack right redzone:     f3
  Stack after return:      f5
  Stack use after scope:   f8
  Global redzone:          f9
  Global init order:       f6
  Poisoned by user:        f7
  Container overflow:      fc
  Array cookie:            ac
  Intra object redzone:    bb
  ASan internal:           fe
  Left alloca redzone:     ca
  Right alloca redzone:    cb
==3792==ABORTING

-fdump-tree-gimple:
GCC 7:

g++-7  /tmp/snippet.cc -fdump-tree-gimple=/dev/stdout
int main() ()
{
  int D.3323;

  {
    struct ArrayView a;

    try
      {
        a.m_pointer = &._18;
        a.m_size = 3;
        _1 = ArrayView<const char>::operator[] (&a, 0);
        _2 = *_1;
        D.3323 = (int) _2;
        return D.3323;
      }
    finally
      {
        a = {CLOBBER};
      }
  }
  D.3323 = 0;
  return D.3323;
}

GCC 8:

g++  /tmp/snippet.cc -fdump-tree-gimple=/dev/stdout
main ()
{
  const struct initializer_list D.3377;
  const char D.3376[3];
  int D.3403;

  {
    struct ArrayView a;

    try
      {
        D.3376[0] = 97;
        D.3376[1] = 98;
        D.3376[2] = 99;
        try
          {
            D.3377._M_array = &D.3376;
            D.3377._M_len = 3;
            try
              {
                ArrayView<const char>::ArrayView (&a, &D.3377);
              }
            finally
              {
                D.3377 = {CLOBBER};
              }
          }
        finally
          {
            D.3376 = {CLOBBER};
          }
        _1 = ArrayView<const char>::operator[] (&a, 0);
        _2 = *_1;
        D.3403 = (int) _2;
        return D.3403;
      }
    finally
      {
        a = {CLOBBER};
      }
  }
  D.3403 = 0;
  return D.3403;
}