[Bug c++/105424] New: Bogus -Wstringop-overread with non-overread condition

["byteslice at airmail dot cc" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105424

            Bug ID: 105424
           Summary: Bogus -Wstringop-overread with non-overread condition
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: byteslice at airmail dot cc
  Target Milestone: ---

Created attachment 52897
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=52897&action=edit
Cvised example

On gcc 12.0.1 20220413 (Fedora 36 Beta), with c++ -std=c++20 -O1
-Werror=stringop-overread, the attachment fails to compile, with the following
message:

In function 'void boost::memmove(I, F) [with I = move_iterator<int*>; F =
int]',
    inlined from 'F boost::uninitialized_copy_alloc(Allocator, I, F) [with
Allocator = vector_alloc_holder; I = move_iterator<int*>; F = int]' at
<source>:67:10,
    inlined from 'void
boost::vector::priv_uninitialized_construct_at_end(InpIt, InpIt) [with InpIt =
boost::move_iterator<int*>]' at <source>:91:45,
    inlined from 'void boost::vector::assign(FwdIt, FwdIt) [with FwdIt =
boost::move_iterator<int*>]' at <source>:87:42,
    inlined from 'boost::small_vector::small_vector(boost::small_vector&&)' at
<source>:106:11,
    inlined from 'Stack::Stack(Stack&&)' at <source>:113:8,
    inlined from 'pair<_T2>::pair(_U1, _U2) [with _U1 = int; _U2 = Stack; _T2 =
Stack]' at <source>:5:24,
    inlined from 'pair<Stack> Stack::Pop() const' at <source>:118:67:
<source>:63:14: error: 'void* memmove(void*, const void*, long unsigned int)'
reading 9 or more bytes from a region of size 4 [-Werror=stringop-overread]
   63 |     ::memmove(dest_raw, beg_raw, n);
      |     ~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~
<source>: In member function 'pair<Stack> Stack::Pop() const':
<source>:103:9: note: source object '__trans_tmp_4' of size 4
  103 |     int __trans_tmp_4;
      |         ^~~~~~~~~~~~~
cc1plus: some warnings being treated as errors
Compiler returned: 1

This warning is bogus because the memmove is guarded by a condition that
prevents the size from being more than 4. The bogus warning does not appear in
older versions of GCC.

Adding -fno-inline to options allows compilation to succeed.