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From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/94261] [10 Regression] ICE in
 vect_get_vec_def_for_operand_1 for 3-element condition reduction
Date: Mon, 23 Mar 2020 11:26:01 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D94261

--- Comment #6 from Richard Biener <rguenth at gcc dot gnu.org> ---
(In reply to rsandifo@gcc.gnu.org from comment #5)
> (In reply to Richard Biener from comment #3)
> > (In reply to Richard Biener from comment #2)
> > > when placing gcc_unreachable () at the swapping place and most testca=
ses
> > > still pass when removing the IL operand swapping, only vect-cselim-1.c
> > > runfails (investigating).
> >=20
> > Ah, SLP ultimately fails here so the scalar IL is broken by the operati=
on
> > code adjustment.  In the end we should be able to avoid doing tree code
> > adjustments as well since we're swapping to make the code the same
> > as the first stmts code and we only ever look at the first scalar stmt
> > during SLP code-gen/analysis.=20
>=20
> Yeah, started wondering about that later too...

So there's probably a single path where this is not true which is when we
go through vect_attempt_slp_rearrange_stmts thus when we have a SLPed
set of cond-reductions.  I'm trying to come up with a testcase ...

But I think the cure here should be to punt on vect_slp_rearrange_stmts,
do you agree?=