[Bug rtl-optimization/90271] [missed-optimization] failure to keep variables in registers during "faux" memcpy

[eyalroz at technion dot ac.il]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90271

--- Comment #1 from Eyal Rozenberg <eyalroz at technion dot ac.il> ---
Can also reproduce this in C, with slightly different code:

int replace_bytes_3(int v1 ,char v2)
{
   memcpy( (void*) (((char*)&v1)+1) , &v2 , sizeof(v2) );
   return v1;
}

int foo3()
{
  int x = 3;
  char c = 1;
  return replace_bytes_3(x,c);
}


GodBolt: https://godbolt.org/z/1K89xh

Again, clang optimizes this correctly. Note specifically the way it handles the
non-inlined replace_bytes_3.