[Bug tree-optimization/111950] [14 Regression] ICE in compute_live_loop_exits, at tree-ssa-loop-manip.cc:250 since r14-4786-gd118738e71c

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111950

--- Comment #5 from Richard Biener <rguenth at gcc dot gnu.org> ---
t.c:6:10: note:   init: stmt relevant? iftmp.0_9 = _32 ? 1 : iftmp.0_39;
t.c:6:10: note:   vec_stmt_relevant_p: used out of loop.
t.c:6:10: note:   vect_is_simple_use: operand _1 != 0, type of def: external
t.c:6:10: note:   vect_is_simple_use: operand (unsigned int) a.3_23, type of
def: external
t.c:6:10: note:   mark relevant 0, live 1: iftmp.0_9 = _32 ? 1 : iftmp.0_39;
t.c:6:10: note:   last stmt in pattern. don't mark relevant/live.
t.c:6:10: note:   vec_stmt_relevant_p: forcing live pattern stmt relevant.
t.c:6:10: note:   mark relevant 1, live 1: patt_43 = _32 != 0 ? 1 : iftmp.0_39;
t.c:6:10: note:   init: stmt relevant? c_I_lsm.18_38 = _32 ? 1 : a.3_23;
t.c:6:10: note:   vec_stmt_relevant_p: used out of loop.
t.c:6:10: note:   vec_stmt_relevant_p: used out of loop.
t.c:6:10: note:   vect_is_simple_use: operand _1 != 0, type of def: external
t.c:6:10: note:   vect_is_simple_use: operand a, type of def: external
t.c:6:10: note:   mark relevant 0, live 1: c_I_lsm.18_38 = _32 ? 1 : a.3_23;
t.c:6:10: note:   last stmt in pattern. don't mark relevant/live.
t.c:6:10: note:   vec_stmt_relevant_p: forcing live pattern stmt relevant.
t.c:6:10: note:   mark relevant 1, live 1: patt_41 = _32 != 0 ? 1 : a.3_23;
t.c:6:10: note:   init: stmt relevant? _37 = d.12_13 + 1;
t.c:6:10: note:   init: stmt relevant? if (_37 != 0)
t.c:6:10: note:   worklist: examine stmt: patt_41 = _32 != 0 ? 1 : a.3_23;
t.c:6:10: note:   vect_is_simple_use: operand _1 != 0, type of def: external
t.c:6:10: note:   vect_is_simple_use: operand 0, type of def: constant
t.c:6:10: note:   vect_is_simple_use: operand a, type of def: external
t.c:6:10: note:   worklist: examine stmt: patt_43 = _32 != 0 ? 1 : iftmp.0_39;
t.c:6:10: note:   vect_is_simple_use: operand _1 != 0, type of def: external
t.c:6:10: note:   vect_is_simple_use: operand 0, type of def: constant
t.c:6:10: note:   vect_is_simple_use: operand (unsigned int) a.3_23, type of
def: external

now, if-conversion managed to CSE the LC PHI node:

  <bb 19> [local count: 16140304]:
  # prephitmp_40 = PHI <c_I_lsm.18_38(11), prephitmp_34(23)>
  # c_I_lsm.18_24 = PHI <c_I_lsm.18_38(11), c_I_lsm.18_33(23)>
  # iftmp.0_21 = PHI <iftmp.0_9(11), iftmp.0_8(23)>

that triggers "interesting" behavior in vectorizable_live_operation which
inserts a PHI for the vectorized c_I_lsm.18_38.  It will remove the
_first_ PHI node using the old scalar (prephitmp_40) and insert a copy
for that.  It leaves the second around, but will then, running into the
remaining USE, replace all uses of c_I_lsm.18_24 with the vectorized
result:

<bb 32> [local count: 14526274]:
# c_I_lsm.18_59 = PHI <c_I_lsm.18_38(11)>
# d.12_61 = PHI <_37(11)>
# vect_patt_43.28_82 = PHI <vect_patt_43.28_81(11)>
# vect_patt_41.29_91 = PHI <vect_patt_41.29_90(11)>
_92 = BIT_FIELD_REF <vect_patt_41.29_91, 32, 96>;
prephitmp_58 = _92;
_83 = BIT_FIELD_REF <vect_patt_43.28_82, 32, 96>;
iftmp.0_60 = _83;
niters_vector_mult_vf.26_68 = bnd.25_67 << 2;
_70 = (int) niters_vector_mult_vf.26_68;
tmp.27_69 = d.12_5 + _70;
if (niters.24_48 == niters_vector_mult_vf.26_68)

this all doesn't make much sense to me ... doing the "obvious" doesn't fix
this bug.  It seems things are wrong already when the epilog peeling happens
where for the merge PHI after the epilog we somehow failed to update
the PHI node for c_I_lsm.18_73.

Looks like we didn't get rid of 'find_guard_arg' ... and it relies on
get_current_def which in turn relies on "copying" that info from
the scalar copy to the original loop (the magic in
slpeel_duplicate_current_defs_from_edges).  That was all fragile
in the past, I guess it's now simply broken, at least for the special
case we have here.