Robin Dapp writes:
> 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 need_temps;
>
> - if (!cc_cmp)
> -check_need_temps (then_bb, _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, _temps, cond);
>
>hash_map 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 ();
Why do we need the push_topmost_sequence/pop_topmost_sequence?
start_sequence/end_sequence ought to be enough.
> +
> + {
> + start_sequence ();
> + temp_dest1 = noce_emit_cmove (if_info, temp, cond_code,
> + x, y, new_val, old_val, NULL_RTX);
Nit: arguments should be indented below "if_info, ".
> +
> + /* 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 += 1;
> + }
> + end_sequence ();
Don't think we should use fake costs for failure. Just setting seq1 to
null should be enough, and should be OK for the recog_memoized case too.
Can break the loop as soon as we find a failure.
> + }
> +
> + /* 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 += 1;
> + }
> + end_sequence ();
> + }
Same comments here. Would be nice to split this out into a subroutine
rather than duplicate it.
Thanks,
Richard
>
> - /* 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 ();
> +
