[Bug target/99912] Unnecessary / inefficient spilling of AVX2 ymm registers

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99912

--- Comment #10 from Richard Biener <rguenth at gcc dot gnu.org> ---
So with the latest patches I now see real spilling dominating (oops).  I also
see, on the GIMPLE level

  _64425 = (unsigned long) SR.3210_122492;
  _64416 = _64425 + ivtmp.5307_121062;
  _62971 = (double &) _64416;
  __builtin_ia32_maskloadpd256 (_62971, _61513);

that is, dead masked loads (that's odd).

There's also still some dead / redundant code from the abstraction to remove.