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From: "glisse at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/94314] New: [10 Regression] Optimizing mismatched
 new/delete pairs
Date: Tue, 24 Mar 2020 21:59:51 +0000
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X-Bugzilla-Version: 10.0
X-Bugzilla-Keywords: wrong-code
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D94314

            Bug ID: 94314
           Summary: [10 Regression] Optimizing mismatched new/delete pairs
           Product: gcc
           Version: 10.0
            Status: UNCONFIRMED
          Keywords: wrong-code
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: glisse at gcc dot gnu.org
  Target Milestone: ---

(originally posted at
https://gcc.gnu.org/legacy-ml/gcc-patches/2019-08/msg00276.html , I don't k=
now
if we will do something about it, but it seems worth documenting it in
bugzilla)

Now that we optimize class-specific operator new/delete pairs (but you coul=
d do
the same with the global replacable ones as well):

#include <stdio.h>
int count =3D 0;
struct A {
  __attribute__((malloc,noinline))
  static void* operator new(unsigned long sz){++count;return ::operator
new(sz);}
  static void operator delete(void* ptr){--count;::operator delete(ptr);}
};
int main(){
  delete new A;
  printf("%d\n",count); // Should print 0.
}

If we do not inline anything, we can remove the pair and nothing touches co=
unt.
If we inline both new and delete, we can then remove the inner pair instead,
count increases and decreases, fine. If we inline only one of them, and DCE=
 the
mismatched pair new/delete, we get something inconsistent (count is -1).

This seems to indicate we should check that the new and delete match someho=
w...=