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From: "amker at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/97627] [9/10/11 Regression] loop end condition missing -
 endless loop with -fPIC
Date: Mon, 25 Jan 2021 11:29:53 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D97627

--- Comment #11 from bin cheng <amker at gcc dot gnu.org> ---
(In reply to bin cheng from comment #10)
> hmm,
> For below basic block:
> 128 ;;   basic block 4, loop depth 2, maybe hot
> 129 ;;    prev block 3, next block 9, flags: (NEW, VISITED)
> 130 ;;    pred:       3 (FALLTHRU,EXECUTABLE)
> 131 ;;                7 (FALLTHRU,DFS_BACK,EXECUTABLE)
> 132   # RANGE [0, 2147483647] NONZERO 2147483647
> 133   # c_5 =3D PHI <0(3), c_17(7)>
> 134   # .MEM_8 =3D PHI <.MEM_7(3), .MEM_9(7)>
> 135   if (_2 < c_5)
> 136     goto <bb 8>; [INV]
> 137   else
> 138     goto <bb 9>; [INV]
> 139 ;;    succ:       8 (TRUE_VALUE,EXECUTABLE)
> 140 ;;                9 (FALSE_VALUE,EXECUTABLE)
>=20
> Code in :
> 4276=20
> 4277   basic_block *body =3D get_loop_body (loop);
> 4278   exits =3D get_loop_exit_edges (loop, body);
> 4279   likely_exit =3D single_likely_exit (loop, exits);
> 4280   FOR_EACH_VEC_ELT (exits, i, ex)
> 4281     {
> 4282       if (ex =3D=3D likely_exit)
> 4283         {
> 4284           gimple *stmt =3D last_stmt (ex->src);
> 4285           if (stmt !=3D NULL)
> 4286             {
>=20
> gets three exit edges, one of which is <bb4 -> bb1>, as a result, 0 niter=
 is
> computed for this exit in function number_of_iterations_exit_assumptions.=
=20
> This seems strange, is it a fake edge added for some reason?
>=20
> Thanks

Right, it's added by connect_infinite_loops_to_exit.=