This patch duplicates the previous noce_emit_cmove logic. First it passes the canonical comparison emits the sequence and costs it. Then, a second, separate sequence is created by passing the cc compare we extracted before. The costs of both sequences are compared and the cheaper one is emitted. --- gcc/ifcvt.c | 106 +++++++++++++++++++++++++++++++++++++++++++++++----- 1 file changed, 97 insertions(+), 9 deletions(-)
diff --git a/gcc/ifcvt.c b/gcc/ifcvt.c index 3db707e1fd1..955f9541f60 100644 --- a/gcc/ifcvt.c +++ b/gcc/ifcvt.c @@ -3208,8 +3208,11 @@ noce_convert_multiple_sets (struct noce_if_info *if_info) hash_map<rtx, bool> need_temps; - if (!cc_cmp) - check_need_temps (then_bb, &need_temps, cond); + /* If we newly set a CC before a cmov, we might need a temporary + even though the compare will be removed by a later pass. Costing + of a sequence with these will be inaccurate. */ + + check_need_temps (then_bb, &need_temps, cond); hash_map<rtx, bool> temps_created; @@ -3298,18 +3301,103 @@ noce_convert_multiple_sets (struct noce_if_info *if_info) old_val = lowpart_subreg (dst_mode, old_val, src_mode); } - /* Actually emit the conditional move. */ - rtx temp_dest = noce_emit_cmove (if_info, temp, cond_code, - x, y, new_val, old_val, cc_cmp); + /* Try emitting a conditional move passing the backend the + canonicalized comparison. This can e.g. be used to recognize + expressions like + + if (a < b) + { + ... + b = a; + } + + A backend can recognize this and emit a min/max insn. + We will still emit a superfluous CC comparison before the + min/max, though, which complicates costing. + */ + + rtx_insn *seq, *seq1 = 0, *seq2 = 0; + rtx temp_dest, temp_dest1, temp_dest2; + unsigned int cost1 = 0, cost2 = 0; + bool speed_p = if_info->speed_p; + push_topmost_sequence (); + + { + start_sequence (); + temp_dest1 = noce_emit_cmove (if_info, temp, cond_code, + x, y, new_val, old_val, NULL_RTX); + + /* If we failed to expand the conditional move, drop out and don't + try to continue. */ + if (temp_dest1 == NULL_RTX) + { + seq1 = NULL; + cost1 = COSTS_N_INSNS (100); + } + else + { + seq1 = get_insns (); + cost1 = seq_cost (seq1, speed_p); + rtx_insn *ii; + for (ii = seq1; ii; ii = NEXT_INSN (ii)) + if (recog_memozied (ii) == -1) + cost1 += 10000; + } + end_sequence (); + } + + /* Now try emitting one passing a non-canonicalized cc comparison. + This allows the backend to emit a cmov directly without additional + compare. */ + { + start_sequence (); + temp_dest2 = noce_emit_cmove (if_info, target, cond_code, + x, y, new_val, old_val, cc_cmp); + + /* If we failed to expand the conditional move, drop out and don't + try to continue. */ + if (temp_dest2 == NULL_RTX) + { + seq2 = NULL; + cost2 = COSTS_N_INSNS (100); + } + else + { + seq2 = get_insns (); + cost2 = seq_cost (seq2, speed_p); + rtx_insn *ii; + for (ii = seq2; ii; ii = NEXT_INSN (ii)) + if (recog_memozied (ii) == -1) + cost2 += 10000; + } + end_sequence (); + } - /* If we failed to expand the conditional move, drop out and don't - try to continue. */ - if (temp_dest == NULL_RTX) + /* Check which version is less expensive. */ + if (cost1 <= cost2 && seq1 != NULL_RTX) + { + temp_dest = temp_dest1; + seq = seq1; + } + else if (seq2 != NULL_RTX) + { + /* We do not require a temp register, so remove it from the list. */ + seq = seq2; + temp_dest = temp_dest2; + temps_created.remove (temp); + } + else { + /* Nothing worked, bail out. */ + pop_topmost_sequence (); end_sequence (); - return FALSE; + return false; } + /* End the sub sequence and emit to the main sequence. */ + pop_topmost_sequence (); + emit_insn (seq); + /* Bookkeeping. */ count++; targets.safe_push (target); -- 2.17.0