[Bug middle-end/115597] [15 Regression] vectorizer takes 20+ h compiling 510.parest in SPECCPU2017 since g:46bb4ce4d30ab749d40f6f4cef6f1fb7c7813452

["tnfchris at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115597

--- Comment #4 from Tamar Christina <tnfchris at gcc dot gnu.org> ---
(In reply to Richard Biener from comment #2)
> Ah, I feared this would happen - this case seems to be because of a lot of
> VEC_PERM nodes(?) which are not handled by the CSE process as well as the
> two-operator nodes which lack SLP_TREE_SCALAR_STMTS (we'd need NULL elements
> there, something I need to add anyway).
> 
> The bst_map deals as "visited" map, but nodes not handled there would need
> a "visited" set (but as said above, the plan is to reduce that set to zero).
> 

Ah I see, that makes sense.

> I'll see to reproduce to confirm.  Usually a two-operator node shouldn't
> be too bad since the next non-two-operator one will serve as 'visited' point
> but in this graph we have several adjacent two-operator nodes without any
> intermediate node handled by the bst-map processing code.  I can't reproduce
> with -Ofast -march=znver2 though.
> 

Yeah I forgot to mention I could only reproduce it with LTO and a recent glibc.

Thanks for the fix!