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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/94043] [9/10 Regression] ICE in
 superloop_at_depth, at cfgloop.c:78
Date: Mon, 23 Mar 2020 13:21:48 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D94043

--- Comment #9 from Richard Biener <rguenth at gcc dot gnu.org> ---
OK, so it's indeed vectorizable_live_operation not paying attention to
loop-closed SSA form.

What it should do before building the lane extract is create a _new_
loop-closed PHI node for the vectorized def (vec_lhs), and then
demote the loop-closed PHI node for the scalar def (lhs) which should
_always_ exist to a copy.  So from


 loop;

# lhs' =3D PHI <lhs>


go to

  loop;

# vec_lhs' =3D PHI <vec_lhs>
new_tree =3D BIT_FIELD_REF <vec_lhs', ...>;
lhs' =3D new_tree;

I think you can assert that the block of the loop-closed PHI
(single_exit()->dest) always has a single predecessor, otherwise
things will be more complicated.

Can you try rework the code in this way?  If that's too much just tell
me and I'll take care of this.=