Re: [PATCH v2] powerpc: Add optimized strlen for POWER10

[Raphael M Zinsly <rzinsly@linux.ibm.com>]

Hi Matheus, the patch LGTM with some trivial changes.

On 22/04/2021 09:29, Matheus Castanho via Libc-alpha wrote:
> diff --git a/sysdeps/powerpc/powerpc64/le/power10/strlen.S b/sysdeps/powerpc/powerpc64/le/power10/strlen.S
> new file mode 100644
> index 0000000000..7eb37a8f54
> --- /dev/null
> +++ b/sysdeps/powerpc/powerpc64/le/power10/strlen.S
> @@ -0,0 +1,221 @@
> +/* Optimized strlen implementation for POWER10 LE.
> +   Copyright (C) 2021 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>
> +
> +#ifndef STRLEN
> +# define STRLEN __strlen
> +# define DEFINE_STRLEN_HIDDEN_DEF 1
> +#endif
> +
> +/* TODO: Replace macros by the actual instructions when minimum binutils becomes
> +   >= 2.35.  This is used to keep compatibility with older versions.  */
> +#define VEXTRACTBM(rt,vrb)	 \
> +	.long(((4)<<(32-6))	 \
> +	      | ((rt)<<(32-11))	 \
> +	      | ((8)<<(32-16))	 \
> +	      | ((vrb)<<(32-21)) \
> +	      | 1602)
> +
> +#define LXVP(xtp,dq,ra)		   \
> +	.long(((6)<<(32-6))		   \
> +	      | ((((xtp)-32)>>1)<<(32-10)) \
> +	      | ((1)<<(32-11))		   \
> +	      | ((ra)<<(32-16))		   \
> +	      | dq)
> +
> +#define CHECK16(vreg,offset,addr,label) \
> +	lxv	  vreg+32,offset(addr);	\
> +	vcmpequb. vreg,vreg,v18;	\
> +	bne	  cr6,L(label);
> +
> +/* Load 4 quadwords, merge into one VR for speed and check for NULLs.  r6 has #
> +   of bytes already checked.  */
> +#define CHECK64(offset,addr,label)	    \
> +	li	  r6,offset;		    \
> +	LXVP(v4+32,offset,addr);	    \
> +	LXVP(v6+32,offset+32,addr);	    \
> +	vminub	  v14,v4,v5;		    \
> +	vminub	  v15,v6,v7;		    \
> +	vminub	  v16,v14,v15;		    \
> +	vcmpequb. v0,v16,v18;		    \
> +	bne	  cr6,L(label)
> +
> +# define TAIL(vreg,increment)	   \

nit: the space before define is not needed.

> +	vctzlsbb  r4,vreg;	   \
> +	subf	  r3,r3,r5;	   \
> +	addi	  r4,r4,increment; \
> +	add	  r3,r3,r4;	   \
> +	blr
> +
> +/* Implements the function
> +
> +   int [r3] strlen (const void *s [r3])
> +
> +   The implementation can load bytes past a matching byte, but only
> +   up to the next 64B boundary, so it never crosses a page.  */
> +
> +.machine power9
> +
> +ENTRY_TOCLESS (STRLEN, 4)
> +	CALL_MCOUNT 1
> +
> +	vspltisb  v18,0
> +	vspltisb  v19,-1
> +
> +	/* Next 16B-aligned address. Prepare address for L(aligned).  */
> +	addi	  r5,r3,16
> +	clrrdi	  r5,r5,4
> +
> +	/* Align data and fill bytes not loaded with non matching char.	 */
> +	lvx	  v0,0,r3
> +	lvsr	  v1,0,r3
> +	vperm	  v0,v19,v0,v1
> +
> +	vcmpequb. v6,v0,v18
> +	beq	  cr6,L(aligned)
> +
> +	vctzlsbb  r3,v6
> +	blr
> +
> +	/* Test more 112B, 16B at a time.  The main loop is optimized for longer

s/112B/176B/

> +	   strings, so checking the first bytes in 16B chunks benefits a lot
> +	   small strings.  */
> +	.p2align 5
> +L(aligned):

-- 
Raphael Moreira Zinsly