[Bug tree-optimization/101120] vn_reference_maybe_forwprop_address can take much compile-time

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101120

--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
Created attachment 51034
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=51034&action=edit
patch

That fixes the attached but we also have loads of dead loads around which
exposes
the IV opts issue at -Ofast where IVOPTs analyzes all the dead loads
with zero-use LHS.  While we have

          PUSH_INSERT_PASSES_WITHIN (pass_vectorize)
              NEXT_PASS (pass_dce);
          POP_INSERT_PASSES ()

there's no such attempt after SLP passes.

But pruning the DR chain after SLP permute is possible as another hack.