https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110491
Richard Biener <rguenth at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- Ever confirmed|0 |1 Assignee|unassigned at gcc dot gnu.org |rguenth at gcc dot gnu.org Status|RESOLVED |ASSIGNED Resolution|DUPLICATE |--- Last reconfirmed| |2023-07-04 --- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> --- So the issue here is phiopt4 doing <bb 6> [local count: 1073741824]: - if (c_lsm_flag.14_16 != 0) - goto <bb 8>; [66.67%] - else - goto <bb 7>; [33.33%] - - <bb 7> [local count: 357913944]: - - <bb 8> [local count: 1073741824]: + _26 = ~c_lsm_flag.14_16; + _14 = (int) _26; # RANGE [irange] int [0, 1] NONZERO 0x1 - # prephitmp_27 = PHI <1(7), c_lsm.13_3(6)> - c = prephitmp_27; + _4 = c_lsm.13_3 | _14; + c = _4; return; via phiopt match-simplify trying: c_lsm_flag.14_16 != 0 ? c_lsm.13_3 : 1 Matching expression match.pd:1991, gimple-match-5.cc:23 Matching expression match.pd:1991, gimple-match-5.cc:23 Matching expression match.pd:1991, gimple-match-5.cc:23 Matching expression match.pd:1948, gimple-match-7.cc:20 Matching expression match.pd:2480, gimple-match-4.cc:35 Matching expression match.pd:2483, gimple-match-3.cc:66 Matching expression match.pd:2490, gimple-match-2.cc:58 Applying pattern match.pd:6459, gimple-match-10.cc:12767 Applying pattern match.pd:1378, gimple-match-5.cc:7352 Applying pattern match.pd:1886, gimple-match-1.cc:1232 Applying pattern match.pd:4748, gimple-match-4.cc:15651 Folded into the sequence: _13 = (int) c_lsm_flag.14_16; _26 = ~c_lsm_flag.14_16; _14 = (int) _26; _4 = c_lsm.13_3 | _14; Removing basic block 7 but <bb 3> [local count: 9761289309]: # RANGE [irange] int [0, 1] NONZERO 0x1 # c_lsm.13_3 = PHI <_17(D)(2), _11(5)> so we have an uninitialized use here. The following fixes this. diff --git a/gcc/tree-ssa-phiopt.cc b/gcc/tree-ssa-phiopt.cc index 31a7c39e405..467c9fd108a 100644 --- a/gcc/tree-ssa-phiopt.cc +++ b/gcc/tree-ssa-phiopt.cc @@ -785,6 +785,13 @@ match_simplify_replacement (basic_block cond_bb, basic_block middle_bb, arg_false = arg0; } + /* Do not make conditional undefs unconditional. */ + if ((TREE_CODE (arg_true) == SSA_NAME + && ssa_name_maybe_undef_p (arg_true)) + || (TREE_CODE (arg_false) == SSA_NAME + && ssa_name_maybe_undef_p (arg_false))) + return false; + tree type = TREE_TYPE (gimple_phi_result (phi)); result = gimple_simplify_phiopt (early_p, type, stmt, arg_true, arg_false,