C: assigning void* to itself when passed in to a function

Question

I'm reading through the LZMA SDK source code and noticed that they assign pointers passed into a method to themselves - example (from the SDK, C/Util/7z/7zAlloc.c):

void *SzAlloc(void *p, size_t size)
{
  p = p;     <-- !
  if (size == 0)
    return 0;
  #ifdef _SZ_ALLOC_DEBUG
  fprintf(stderr, "\nAlloc %10d bytes; count = %10d", size, g_allocCount);
  g_allocCount++;
  #endif
  return malloc(size);
}

Can someone explain why they do this?

Answer 1

To avoid compiler warnings on unused parameters.