powerpc: Optimized strncmp for power10

This patch is based on __strcmp_power10.

Improvements from __strncmp_power9:

    1. Uses new POWER10 instructions
       - This code uses lxvp to decrease contention on load
	 by loading 32 bytes per instruction.

    2. Performance implication
       - This version has around 38% better performance on average.
       - Minor performance regression is seen for few small sizes
	 and specific combination of alignments.

Signed-off-by: Amrita H S <amritahs@linux.ibm.com>
Reviewed-by: Peter Bergner <bergner@linux.ibm.com>

sysdeps/powerpc/powerpc64/le/power10/strncmp.S

@@ -0,0 +1,271 @@
+/* Optimized strncmp implementation for PowerPC64/POWER10.
+   Copyright (C) 2024 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+#include <sysdep.h>
+
+/* Implements the function
+
+   int [r3] strncmp (const char *s1 [r3], const char *s2 [r4], size_t [r5] n)
+
+   The implementation uses unaligned doubleword access to avoid specialized
+   code paths depending of data alignment for first 32 bytes and uses
+   vectorised loops after that.  */
+
+#ifndef STRNCMP
+# define STRNCMP strncmp
+#endif
+
+/* TODO: Change this to actual instructions when minimum binutils is upgraded
+   to 2.27.  Macros are defined below for these newer instructions in order
+   to maintain compatibility.  */
+
+#define LXVP(xtp,dq,ra)              \
+	.long(((6)<<(32-6))          \
+	| ((((xtp)-32)>>1)<<(32-10)) \
+	| ((1)<<(32-11))             \
+	| ((ra)<<(32-16))            \
+	| dq)
+
+#define COMPARE_16(vreg1,vreg2,offset) \
+	lxv	  vreg1+32,offset(r3); \
+	lxv	  vreg2+32,offset(r4); \
+	vcmpnezb. v7,vreg1,vreg2;      \
+	bne	  cr6,L(different);    \
+	cmpldi	  cr7,r5,16;           \
+	ble	  cr7,L(ret0);         \
+	addi	  r5,r5,-16;
+
+#define COMPARE_32(vreg1,vreg2,offset,label1,label2) \
+	LXVP(vreg1+32,offset,r3);                    \
+	LXVP(vreg2+32,offset,r4);                    \
+	vcmpnezb. v7,vreg1+1,vreg2+1;                \
+	bne	  cr6,L(label1);                     \
+	vcmpnezb. v7,vreg1,vreg2;                    \
+	bne	  cr6,L(label2);                     \
+	cmpldi	  cr7,r5,32;                         \
+	ble	  cr7,L(ret0);                       \
+	addi	  r5,r5,-32;
+
+#define TAIL_FIRST_16B(vreg1,vreg2) \
+	vctzlsbb r6,v7;             \
+	cmpld	 cr7,r5,r6;         \
+	ble	 cr7,L(ret0);       \
+	vextubrx r5,r6,vreg1;       \
+	vextubrx r4,r6,vreg2;       \
+	subf	 r3,r4,r5;          \
+	blr;
+
+#define TAIL_SECOND_16B(vreg1,vreg2) \
+	vctzlsbb r6,v7;              \
+	addi	 r0,r6,16;           \
+	cmpld	 cr7,r5,r0;          \
+	ble	 cr7,L(ret0);        \
+	vextubrx r5,r6,vreg1;        \
+	vextubrx r4,r6,vreg2;        \
+	subf	 r3,r4,r5;           \
+	blr;
+
+#define CHECK_N_BYTES(reg1,reg2,len_reg) \
+	sldi	  r6,len_reg,56;	 \
+	lxvl	  32+v4,reg1,r6;	 \
+	lxvl	  32+v5,reg2,r6;	 \
+	add	  reg1,reg1,len_reg;	 \
+	add	  reg2,reg2,len_reg;	 \
+	vcmpnezb  v7,v4,v5;		 \
+	vctzlsbb  r6,v7;		 \
+	cmpld	  cr7,r6,len_reg;	 \
+	blt	  cr7,L(different);	 \
+	cmpld	  cr7,r5,len_reg;	 \
+	ble	  cr7,L(ret0);		 \
+	sub	  r5,r5,len_reg;	 \
+
+	/* TODO: change this to .machine power10 when the minimum required
+	 binutils allows it.  */
+	.machine  power9
+ENTRY_TOCLESS (STRNCMP, 4)
+	/* Check if size is 0.  */
+	cmpdi	 cr0,r5,0
+	beq	 cr0,L(ret0)
+	andi.   r7,r3,4095
+	andi.   r8,r4,4095
+	cmpldi  cr0,r7,4096-16
+	cmpldi  cr1,r8,4096-16
+	bgt     cr0,L(crosses)
+	bgt     cr1,L(crosses)
+	COMPARE_16(v4,v5,0)
+	addi	r3,r3,16
+	addi	r4,r4,16
+
+L(crosses):
+	andi.	 r7,r3,15
+	subfic	 r7,r7,16	/* r7(nalign1) = 16 - (str1 & 15).  */
+	andi.	 r9,r4,15
+	subfic	 r8,r9,16	/* r8(nalign2) = 16 - (str2 & 15).  */
+	cmpld	 cr7,r7,r8
+	beq	 cr7,L(same_aligned)
+	blt	 cr7,L(nalign1_min)
+
+	/* nalign2 is minimum and s2 pointer is aligned.  */
+	CHECK_N_BYTES(r3,r4,r8)
+	/* Are we on the 64B hunk which crosses a page?  */
+	andi.   r10,r3,63       /* Determine offset into 64B hunk.  */
+	andi.   r8,r3,15        /* The offset into the 16B hunk.  */
+	neg     r7,r3
+	andi.   r9,r7,15        /* Number of bytes after a 16B cross.  */
+	rlwinm. r7,r7,26,0x3F   /* ((r4-4096))>>6&63.  */
+	beq     L(compare_64_pagecross)
+	mtctr   r7
+	b       L(compare_64B_unaligned)
+
+	/* nalign1 is minimum and s1 pointer is aligned.  */
+L(nalign1_min):
+	CHECK_N_BYTES(r3,r4,r7)
+	/* Are we on the 64B hunk which crosses a page?  */
+	andi.   r10,r4,63       /* Determine offset into 64B hunk.  */
+	andi.   r8,r4,15        /* The offset into the 16B hunk.  */
+	neg     r7,r4
+	andi.   r9,r7,15        /* Number of bytes after a 16B cross.  */
+	rlwinm. r7,r7,26,0x3F   /* ((r4-4096))>>6&63.  */
+	beq     L(compare_64_pagecross)
+	mtctr   r7
+
+	.p2align 5
+L(compare_64B_unaligned):
+	COMPARE_16(v4,v5,0)
+	COMPARE_16(v4,v5,16)
+	COMPARE_16(v4,v5,32)
+	COMPARE_16(v4,v5,48)
+	addi    r3,r3,64
+	addi    r4,r4,64
+	bdnz    L(compare_64B_unaligned)
+
+	/* Cross the page boundary of s2, carefully. Only for first
+	iteration we have to get the count of 64B blocks to be checked.
+	From second iteration and beyond, loop counter is always 63.  */
+L(compare_64_pagecross):
+	li      r11, 63
+	mtctr   r11
+	cmpldi  r10,16
+	ble     L(cross_4)
+	cmpldi  r10,32
+	ble     L(cross_3)
+	cmpldi  r10,48
+	ble     L(cross_2)
+L(cross_1):
+	CHECK_N_BYTES(r3,r4,r9)
+	CHECK_N_BYTES(r3,r4,r8)
+	COMPARE_16(v4,v5,0)
+	COMPARE_16(v4,v5,16)
+	COMPARE_16(v4,v5,32)
+	addi    r3,r3,48
+	addi    r4,r4,48
+	b       L(compare_64B_unaligned)
+L(cross_2):
+	COMPARE_16(v4,v5,0)
+	addi    r3,r3,16
+	addi    r4,r4,16
+	CHECK_N_BYTES(r3,r4,r9)
+	CHECK_N_BYTES(r3,r4,r8)
+	COMPARE_16(v4,v5,0)
+	COMPARE_16(v4,v5,16)
+	addi    r3,r3,32
+	addi    r4,r4,32
+	b       L(compare_64B_unaligned)
+L(cross_3):
+	COMPARE_16(v4,v5,0)
+	COMPARE_16(v4,v5,16)
+	addi    r3,r3,32
+	addi    r4,r4,32
+	CHECK_N_BYTES(r3,r4,r9)
+	CHECK_N_BYTES(r3,r4,r8)
+	COMPARE_16(v4,v5,0)
+	addi    r3,r3,16
+	addi    r4,r4,16
+	b       L(compare_64B_unaligned)
+L(cross_4):
+	COMPARE_16(v4,v5,0)
+	COMPARE_16(v4,v5,16)
+	COMPARE_16(v4,v5,32)
+	addi    r3,r3,48
+	addi    r4,r4,48
+	CHECK_N_BYTES(r3,r4,r9)
+	CHECK_N_BYTES(r3,r4,r8)
+	b       L(compare_64B_unaligned)
+
+L(same_aligned):
+	CHECK_N_BYTES(r3,r4,r7)
+	/* Align s1 to 32B and adjust s2 address.
+	   Use lxvp only if both s1 and s2 are 32B aligned.  */
+	COMPARE_16(v4,v5,0)
+	COMPARE_16(v4,v5,16)
+	COMPARE_16(v4,v5,32)
+	COMPARE_16(v4,v5,48)
+	addi	r3,r3,64
+	addi	r4,r4,64
+	COMPARE_16(v4,v5,0)
+	COMPARE_16(v4,v5,16)
+	addi	r5,r5,32
+
+	clrldi  r6,r3,59
+	subfic	r7,r6,32
+	add	r3,r3,r7
+	add	r4,r4,r7
+	subf	r5,r7,r5
+	andi.	r7,r4,0x1F
+	beq	cr0,L(32B_aligned_loop)
+
+	.p2align 5
+L(16B_aligned_loop):
+	COMPARE_16(v4,v5,0)
+	COMPARE_16(v4,v5,16)
+	COMPARE_16(v4,v5,32)
+	COMPARE_16(v4,v5,48)
+	addi	r3,r3,64
+	addi	r4,r4,64
+	b	L(16B_aligned_loop)
+
+	/* Calculate and return the difference.  */
+L(different):
+	TAIL_FIRST_16B(v4,v5)
+
+	.p2align 5
+L(32B_aligned_loop):
+	COMPARE_32(v14,v16,0,tail1,tail2)
+	COMPARE_32(v18,v20,32,tail3,tail4)
+	COMPARE_32(v22,v24,64,tail5,tail6)
+	COMPARE_32(v26,v28,96,tail7,tail8)
+	addi	r3,r3,128
+	addi	r4,r4,128
+	b	L(32B_aligned_loop)
+
+L(tail1): TAIL_FIRST_16B(v15,v17)
+L(tail2): TAIL_SECOND_16B(v14,v16)
+L(tail3): TAIL_FIRST_16B(v19,v21)
+L(tail4): TAIL_SECOND_16B(v18,v20)
+L(tail5): TAIL_FIRST_16B(v23,v25)
+L(tail6): TAIL_SECOND_16B(v22,v24)
+L(tail7): TAIL_FIRST_16B(v27,v29)
+L(tail8): TAIL_SECOND_16B(v26,v28)
+
+	.p2align 5
+L(ret0):
+	li	r3,0
+	blr
+
+END(STRNCMP)
+libc_hidden_builtin_def(strncmp)

sysdeps/powerpc/powerpc64/multiarch/Makefile

@@ -34,7 +34,7 @@ ifneq (,$(filter %le,$(config-machine)))
 sysdep_routines += memchr-power10 memcmp-power10 memcpy-power10 \
 		   memmove-power10 memset-power10 rawmemchr-power9 \
 		   rawmemchr-power10 strcmp-power9 strcmp-power10 \
-		   strncmp-power9 strcpy-power9 stpcpy-power9 \
+		   strncmp-power9 strncmp-power10 strcpy-power9 stpcpy-power9 \
 		   strlen-power9 strncpy-power9 stpncpy-power9 strlen-power10
 endif
 CFLAGS-strncase-power7.c += -mcpu=power7 -funroll-loops

sysdeps/powerpc/powerpc64/multiarch/ifunc-impl-list.c

@@ -164,6 +164,9 @@ __libc_ifunc_impl_list (const char *name, struct libc_ifunc_impl *array,
   /* Support sysdeps/powerpc/powerpc64/multiarch/strncmp.c.  */
   IFUNC_IMPL (i, name, strncmp,
 #ifdef __LITTLE_ENDIAN__
+	      IFUNC_IMPL_ADD (array, i, strncmp, hwcap2 & PPC_FEATURE2_ARCH_3_1
+			      && hwcap & PPC_FEATURE_HAS_VSX,
+			      __strncmp_power10)
 	      IFUNC_IMPL_ADD (array, i, strncmp, hwcap2 & PPC_FEATURE2_ARCH_3_00
 			      && hwcap & PPC_FEATURE_HAS_ALTIVEC,
 			      __strncmp_power9)

sysdeps/powerpc/powerpc64/multiarch/strncmp-power10.S

@@ -0,0 +1,25 @@
+/* Copyright (C) 2024 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+#if defined __LITTLE_ENDIAN__ && IS_IN (libc)
+#define STRNCMP __strncmp_power10
+
+#undef libc_hidden_builtin_def
+#define libc_hidden_builtin_def(name)
+
+#include <sysdeps/powerpc/powerpc64/le/power10/strncmp.S>
+#endif

sysdeps/powerpc/powerpc64/multiarch/strncmp.c

@@ -29,6 +29,7 @@ extern __typeof (strncmp) __strncmp_ppc attribute_hidden;
 extern __typeof (strncmp) __strncmp_power8 attribute_hidden;
 # ifdef __LITTLE_ENDIAN__
 extern __typeof (strncmp) __strncmp_power9 attribute_hidden;
+extern __typeof (strncmp) __strncmp_power10 attribute_hidden;
 # endif
 # undef strncmp
 
@@ -36,6 +37,9 @@ extern __typeof (strncmp) __strncmp_power9 attribute_hidden;
    ifunc symbol properly.  */
 libc_ifunc_redirected (__redirect_strncmp, strncmp,
 # ifdef __LITTLE_ENDIAN__
+			(hwcap2 & PPC_FEATURE2_ARCH_3_1
+			 && hwcap & PPC_FEATURE_HAS_VSX)
+			? __strncmp_power10 :
 			(hwcap2 & PPC_FEATURE2_ARCH_3_00
 			 && hwcap & PPC_FEATURE_HAS_ALTIVEC)
 			? __strncmp_power9 :