[Bug c++/102937] Miscompilation with -O3 and aliasing of char* and size_t

[pinskia at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102937

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 = GPUCA_BUFFER_ALIGNMENT, class S>
  static inline S* getPointerWithAlignment(char*& basePtr, size_t nEntries = 1)
  {
    auto t = reinterpret_cast<size_t>(basePtr);
    auto t1= getPointerWithAlignment<alignment,
S>(reinterpret_cast<size_t&>(basePtr), nEntries);
    basePtr = reinterpret_cast<decltype(basePtr)>(t);
    return t1;
  }

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