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From: "linkw 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: Sun, 22 Mar 2020 08:39:44 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D94043

--- Comment #8 from Kewen Lin <linkw at gcc dot gnu.org> ---
> It's most likely either SCEV or expand_simple_operations looking throuhg
> the single-arg PHI (which we should avoid for LC PHI nodes)

Thanks Richi, I found the loop-closed PHI form was broken after we finished=
 the
vectorization on the loop 2, BB 38 was inserted, the function
gimple_find_edge_insert_loc will get one new BB if the dest has phis, even =
it's
unrelated.

;; basic block 4, loop depth 2
;;  pred:       11
;;              37
...
_15 =3D e2.2_31 + 1;
...
if (ivtmp_59 >=3D 1)
  goto <bb 38>; [100.00%]
else
  goto <bb 11>; [0.00%]
;;  succ:       38
;;              11

;; basic block 38, loop depth 1
;;  pred:       4
_40 =3D BIT_FIELD_REF <vect__15.22_43, 32, 96>;
;;  succ:       33

;; basic block 33, loop depth 1
;;  pred:       38
# _51 =3D PHI <_15(38)>=20
;;  succ:       34

The alternatives seems could be 1) extend the current
gimple_find_edge_insert_loc to handle the phi nodes, if the phis aren't
related, just insert there, otherwise, insert some phis for uses of those s=
tmts
and remove the related phis and create new assignments after those new stmt=
s,
or 2) call rewrite_into_loop_closed_ssa for each successful vectorization.=