From: Robin Dapp <rdapp@linux.ibm.com>
To: gcc-patches@gcc.gnu.org, richard.sandiford@arm.com
Subject: [PATCH v3 7/7] ifcvt: Run second pass if it is possible to omit a temporary.
Date: Mon, 6 Dec 2021 19:43:52 +0100 [thread overview]
Message-ID: <20211206184352.42264-8-rdapp@linux.ibm.com> (raw)
In-Reply-To: <20211206184352.42264-1-rdapp@linux.ibm.com>
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.
---
gcc/ifcvt.c | 33 +++++++++++++++++++++++++++++++--
1 file changed, 31 insertions(+), 2 deletions(-)
diff --git a/gcc/ifcvt.c b/gcc/ifcvt.c
index d1e7db1ee27..3be5bb131df 100644
--- a/gcc/ifcvt.c
+++ b/gcc/ifcvt.c
@@ -3262,6 +3262,11 @@ 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. */
@@ -3305,8 +3310,12 @@ 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;
@@ -3389,6 +3398,8 @@ 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)
{
@@ -3412,6 +3423,24 @@ 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 ());
--
2.31.1
next prev parent reply other threads:[~2021-12-06 18:46 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-12-06 18:43 [PATCH v3 0/7] ifcvt: Convert multiple Robin Dapp
2021-12-06 18:43 ` [PATCH v3 1/7] ifcvt: Check if cmovs are needed Robin Dapp
2021-12-09 1:26 ` Jeff Law
2022-01-10 11:17 ` Robin Dapp
2021-12-06 18:43 ` [PATCH v3 2/7] ifcvt: Allow constants for noce_convert_multiple Robin Dapp
2021-12-08 23:51 ` Jeff Law
2022-01-10 11:17 ` Robin Dapp
2021-12-06 18:43 ` [PATCH v3 3/7] ifcvt: Improve costs handling " Robin Dapp
2021-12-08 23:54 ` Jeff Law
2022-01-10 11:17 ` Robin Dapp
2021-12-06 18:43 ` [PATCH v3 4/7] ifcvt/optabs: Allow using a CC comparison for emit_conditional_move Robin Dapp
2021-12-09 0:11 ` Jeff Law
2021-12-09 17:20 ` Robin Dapp
2021-12-09 17:34 ` Jeff Law
2022-01-10 11:18 ` Robin Dapp
2021-12-06 18:43 ` [PATCH v3 5/7] ifcvt: Try re-using CC for conditional moves Robin Dapp
2021-12-09 1:18 ` Jeff Law
2022-01-10 11:18 ` Robin Dapp
2021-12-06 18:43 ` [PATCH v3 6/7] testsuite/s390: Add tests for noce_convert_multiple Robin Dapp
2021-12-08 23:48 ` Jeff Law
2022-01-10 11:18 ` Robin Dapp
2021-12-06 18:43 ` Robin Dapp [this message]
2021-12-09 1:24 ` [PATCH v3 7/7] ifcvt: Run second pass if it is possible to omit a temporary Jeff Law
2021-12-10 15:06 ` Robin Dapp
2021-12-15 20:24 ` Jeff Law
2022-01-10 11:18 ` Robin Dapp
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