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
