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From: "tnfchris at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug target/104529] [12 Regression] inefficient codegen around
 new/delete
Date: Mon, 14 Feb 2022 19:07:00 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D104529

Tamar Christina <tnfchris at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|[missed optimization]       |[12 Regression] inefficient
                   |inefficient codegen around  |codegen around new/delete
                   |new/delete                  |
             Status|RESOLVED                    |UNCONFIRMED
         Resolution|DUPLICATE                   |---

--- Comment #3 from Tamar Christina <tnfchris at gcc dot gnu.org> ---
I'm re-opening because I don't think it has anything to do with #94294

This is a GCC 12 regression.

In GCC 11 we generated in the mid-end

  <bb 2> [local count: 536870913]:
  _32 =3D operator new (6);
  MEM <unsigned int> [(char * {ref-all})_32] =3D 255;
  MEM <unsigned short> [(char * {ref-all})_32 + 4B] =3D 0;
  operator delete (_32, 6);
  return 56;

and in GCC 12 we now generate

  <bb 2> [local count: 536870913]:
  MEM <vector(4) unsigned char> [(unsigned char *)&D.24688] =3D { 255, 0, 0=
, 0 };
  MEM <vector(2) unsigned char> [(unsigned char *)&D.24688 + 4B] =3D { 0, 0=
 };
  _34 =3D operator new (6);
  MEM <unsigned char[6]> [(char * {ref-all})_34] =3D MEM <unsigned char[6]>
[(char * {ref-all})&D.24688];
  D.24688 =3D{v} {CLOBBER(eol)};
  operator delete (_34, 6);
  return 56;

See https://godbolt.org/z/KKfhxTxnd

Forcing it to keep the stores before the call to new.=