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From: "pinskia at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug c++/102937] Miscompilation with -O3 and aliasing of char* and
 size_t
Date: Mon, 25 Oct 2021 21:17:05 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D102937

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |INVALID
             Status|UNCONFIRMED                 |RESOLVED

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
The code is undefined according to the C++ aliasing rules.  Access pointer
types as size_t is undefined.

Here is a simple fix to the code itself:
  template <size_t alignment =3D GPUCA_BUFFER_ALIGNMENT, class S>
  static inline S* getPointerWithAlignment(char*& basePtr, size_t nEntries =
=3D 1)
  {
    auto t =3D reinterpret_cast<size_t>(basePtr);
    auto t1=3D getPointerWithAlignment<alignment,
S>(reinterpret_cast<size_t&>(basePtr), nEntries);
    basePtr =3D reinterpret_cast<decltype(basePtr)>(t);
    return t1;
  }

  template <size_t alignment =3D GPUCA_BUFFER_ALIGNMENT, class T, class S>
  static inline void computePointerWithAlignment(T*& basePtr, S*& objPtr,
size_t nEntries =3D 1)
  {
    size_t t =3D reinterpret_cast<size_t>(basePtr);
    objPtr =3D getPointerWithAlignment<alignment, S>(t, nEntries);
    basePtr =3D reinterpret_cast<T*>(t);
  }=