[Bug tree-optimization/50417] regression: memcpy with known alignment

[olegendo at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=50417

--- Comment #11 from Oleg Endo <olegendo at gcc dot gnu.org> ---
(In reply to rguenther@suse.de from comment #10)
> 
> What makes the parameter type special?  Would
> 
> void test (const int *a, int *b)
> {
>   std::memcpy ((char *)b, (char *)a, t);
> }
> 
> be invalid to optimize to an aligned copy in your eyes?

I think it's perfectly valid to optimize this case.  It could as well be
something like:

void test (const int *a, int *b)
{
  a[100] = 1;
  b[200] = 2;

  std::memcpy ((char *)b, (char *)a, t);
}

where a[100] and b[200] both would result in 32 bit accesses, not 4x1 byte or
something, because the base pointer is assumed to be int aligned.  Why should
memcpy be any different?