commit dd5a0f8d7d39447025d36ed5305709d38fe3f16b
Author: Robin Dapp <rdapp@linux.ibm.com>
Date: Fri Sep 17 20:22:10 2021 +0200
ifcvt: Run second pass if it is possible to omit a temporary.
If one of the to-be-converted SETs requires the original comparison
(i.e. in order to generate a min/max insn) but no other insn after it
does, we can omit creating temporaries, thus facilitating costing.
@@ -3261,6 +3261,11 @@ noce_convert_multiple_sets (struct noce_if_info *if_info)
need_cmov_or_rewire (then_bb, &need_no_cmov, &rewired_src);
+ int last_needs_comparison = -1;
+ bool second_try = false;
+
+restart:
+
FOR_BB_INSNS (then_bb, insn)
{
/* Skip over non-insns. */
@@ -3302,8 +3307,12 @@ noce_convert_multiple_sets (struct noce_if_info *if_info)
Therefore we introduce a temporary every time we are about to
overwrite a variable used in the check. Costing of a sequence with
these is going to be inaccurate so only use temporaries when
- needed. */
- if (reg_overlap_mentioned_p (target, cond))
+ needed.
+
+ If performing a second try, we know how many insns require a
+ temporary. For the last of these, we can omit creating one. */
+ if (reg_overlap_mentioned_p (target, cond)
+ && (!second_try || count < last_needs_comparison))
temp = gen_reg_rtx (GET_MODE (target));
else
temp = target;
@@ -3386,6 +3395,8 @@ noce_convert_multiple_sets (struct noce_if_info *if_info)
{
seq = seq1;
temp_dest = temp_dest1;
+ if (!second_try)
+ last_needs_comparison = count;
}
else if (seq2 != NULL_RTX)
{
@@ -3409,6 +3420,24 @@ noce_convert_multiple_sets (struct noce_if_info *if_info)
unmodified_insns.safe_push (insn);
}
+ /* If there are insns that overwrite part of the initial
+ comparison, we can still omit creating temporaries for
+ the last of them.
+ As the second try will always create a less expensive,
+ valid sequence, we do not need to compare and can discard
+ the first one. */
+ if (!second_try && last_needs_comparison >= 0)
+ {
+ end_sequence ();
+ start_sequence ();
+ count = 0;
+ targets.truncate (0);
+ temporaries.truncate (0);
+ unmodified_insns.truncate (0);
+ second_try = true;
+ goto restart;
+ }
+
/* We must have seen some sort of insn to insert, otherwise we were
given an empty BB to convert, and we can't handle that. */
gcc_assert (!unmodified_insns.is_empty ());