From 470c6f6418efb9d720d5a86423c396b58c4b8f07 Mon Sep 17 00:00:00 2001
From: Lynn Boger <laboger@linux.vnet.ibm.com>
Date: Mon, 15 May 2023 14:11:30 -0500
Subject: [PATCH] runtime: improve ppc64x memclr for tail bytes

This improves memclr for the last few bytes when
compiling for power9 or earlier.

Change-Id: I46940ebc7e98e27a2e48d4b319acb7d2106a6f29
Reviewed-on: https://go-review.googlesource.com/c/go/+/495035
Run-TryBot: Lynn Boger <laboger@linux.vnet.ibm.com>
Reviewed-by: Paul Murphy <murp@ibm.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Heschi Kreinick <heschi@google.com>
---
 src/runtime/memclr_ppc64x.s | 20 +++++++++++++++-----
 1 file changed, 15 insertions(+), 5 deletions(-)

diff --git a/src/runtime/memclr_ppc64x.s b/src/runtime/memclr_ppc64x.s
index f0b13b40ae..bc4b3fc283 100644
--- a/src/runtime/memclr_ppc64x.s
+++ b/src/runtime/memclr_ppc64x.s
@@ -111,11 +111,21 @@ nozerolarge:
 	STXVL   V0, R3, R7
 	RET
 #else
-	MOVD R5, CTR // set up to clear tail bytes
-zerotailloop:
-	MOVB R0, 0(R3)           // clear single bytes
-	ADD  $1, R3
-	BDNZ zerotailloop // dec ctr, br zerotailloop if ctr not 0
+	CMP   R5, $4
+	BLT   next2
+	MOVW  R0, 0(R3)
+	ADD   $4, R3
+	ADD   $-4, R5
+next2:
+	CMP   R5, $2
+	BLT   next1
+	MOVH  R0, 0(R3)
+	ADD   $2, R3
+	ADD   $-2, R5
+next1:
+	CMP   R5, $0
+	BC    12, 2, LR      // beqlr
+	MOVB  R0, 0(R3)
 	RET
 #endif
 
-- 
2.50.0