[PATCH] riscv:lib: optimize memcmp with ld insn

[Yipeng Zou]

Currently memcmp was implemented in c code(lib/string.c), which compare
memory per byte.

This patch use ld insn compare memory per word to improve. From the test
Results, this will take several times optimized.

Signed-off-by: Yipeng Zou <zouyipeng at huawei.com>
---
 arch/riscv/include/asm/string.h |  3 ++
 arch/riscv/lib/Makefile         |  1 +
 arch/riscv/lib/memcmp.S         | 59 +++++++++++++++++++++++++++++++++
 3 files changed, 63 insertions(+)
 create mode 100644 arch/riscv/lib/memcmp.S

diff --git a/arch/riscv/include/asm/string.h b/arch/riscv/include/asm/string.h
index 909049366555..3337b43d3803 100644
--- a/arch/riscv/include/asm/string.h
+++ b/arch/riscv/include/asm/string.h
@@ -18,6 +18,9 @@ extern asmlinkage void *__memcpy(void *, const void *, size_t);
 #define __HAVE_ARCH_MEMMOVE
 extern asmlinkage void *memmove(void *, const void *, size_t);
 extern asmlinkage void *__memmove(void *, const void *, size_t);
+#define __HAVE_ARCH_MEMCMP
+extern int memcmp(const void *, const void *, size_t);
+
 /* For those files which don't want to check by kasan. */
 #if defined(CONFIG_KASAN) && !defined(__SANITIZE_ADDRESS__)
 #define memcpy(dst, src, len) __memcpy(dst, src, len)
diff --git a/arch/riscv/lib/Makefile b/arch/riscv/lib/Makefile
index 25d5c9664e57..70773bf0c471 100644
--- a/arch/riscv/lib/Makefile
+++ b/arch/riscv/lib/Makefile
@@ -3,6 +3,7 @@ lib-y			+= delay.o
 lib-y			+= memcpy.o
 lib-y			+= memset.o
 lib-y			+= memmove.o
+lib-y			+= memcmp.o
 lib-$(CONFIG_MMU)	+= uaccess.o
 lib-$(CONFIG_64BIT)	+= tishift.o
 
diff --git a/arch/riscv/lib/memcmp.S b/arch/riscv/lib/memcmp.S
new file mode 100644
index 000000000000..83af1c433e6f
--- /dev/null
+++ b/arch/riscv/lib/memcmp.S
@@ -0,0 +1,59 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright (C) 2022 zouyipeng at huawei.com
+ */
+#include <linux/linkage.h>
+#include <asm-generic/export.h>
+#include <asm/asm.h>
+
+/* argrments:
+* a0: addr0
+* a1: addr1
+* a2: size
+*/
+#define addr0	a0
+#define addr1	a1
+#define limit	a2
+
+#define data0	a3
+#define data1	a4
+#define tmp	t3
+#define aaddr	t4
+#define return	a0
+
+/* load and compare */
+.macro LD_CMP op d0 d1 a0 a1 offset
+	\op \d0, 0(\a0)
+	\op \d1, 0(\a1)
+	addi \a0, \a0, \offset
+	addi \a1, \a1, \offset
+	sub tmp, \d0, \d1
+.endm
+
+ENTRY(memcmp)
+	/* test limit aligend with SZREG */
+	andi tmp, limit, SZREG - 1
+	/* load tail */
+	add aaddr, addr0, limit
+	sub aaddr, aaddr, tmp
+	add limit, addr0, limit
+
+.LloopWord:
+	sltu tmp, addr0, aaddr
+	beqz tmp, .LloopByte
+
+	LD_CMP REG_L data0 data1 addr0 addr1 SZREG
+	beqz tmp, .LloopWord
+	j .Lreturn
+
+.LloopByte:
+	sltu tmp, addr0, limit
+	beqz tmp, .Lreturn
+
+	LD_CMP lbu data0 data1 addr0 addr1 1
+	beqz tmp, .LloopByte
+.Lreturn:
+	mv return, tmp
+	ret
+END(memcmp)
+EXPORT_SYMBOL(memcmp);
-- 
2.17.1