[Bug c++/96511] New: Incorrect placement-new warning

[mserdarsanli at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96511

            Bug ID: 96511
           Summary: Incorrect placement-new warning
           Product: gcc
           Version: 10.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: mserdarsanli at gmail dot com
  Target Milestone: ---

Below code causes the warning in the last line, which seems to be incorrect. It
affects all versions starting from GCC 8
Compiler explorer: https://godbolt.org/z/xhf6cr

#include <new>

struct Foo {
    Foo() = default;
    Foo(int _a) : a(_a) {}
    int a = 0;
};

void f()
{
    Foo arr[2];

    new (arr) Foo(10); // ok
    new (arr + 0) Foo(10); // ok
    new (&arr[0]) Foo(10); // ok

    new (&arr[1]) Foo(15); // ok
    new (arr + 1) Foo(15); // warning: placement new constructing an object of
type 'Foo' and size '4' in a region of type 'Foo [2]' and size '0'
[-Wplacement-new=]
}