powerpc: Add optimized rawmemchr for POWER10

Reuse code for optimized strlen to implement a faster version of rawmemchr.
This takes advantage of the same benefits provided by the strlen implementation,
but needs some extra steps. __strlen_power10 code should be unchanged after this
change.

rawmemchr returns a pointer to the char found, while strlen returns only the
length, so we have to take that into account when preparing the return value.

To quickly check 64B, the loop on __strlen_power10 merges the whole block into
16B by using unsigned minimum vector operations (vminub) and checks if there are
any \0 on the resulting vector. The same code is used by rawmemchr if the char c
is 0. However, this approach does not work when c != 0.  We first need to
subtract each byte by c, so that the value we are looking for is converted to a
0, then taking the minimum and checking for nulls works again.

The new code branches after it has compared ~256 bytes and chooses which of the
two strategies above will be used in the main loop, based on the char c. This
extra branch adds some overhead (~5%) for length ~256, but is quickly amortized
by the faster loop for larger sizes.

Compared to __rawmemchr_power9, this version is ~20% faster for length < 256.
Because of the optimized main loop, the improvement becomes ~35% for c != 0
and ~50% for c = 0 for strings longer than 256.

Reviewed-by: Lucas A. M. Magalhaes <lamm@linux.ibm.com>
Reviewed-by: Raphael M Zinsly <rzinsly@linux.ibm.com>

2 files changed, 157 insertions, 25 deletions

diff --git a/sysdeps/powerpc/powerpc64/le/power10/rawmemchr.S b/sysdeps/powerpc/powerpc64/le/power10/rawmemchr.S
new file mode 100644
index 0000000000..5351c2634f
--- /dev/null
+++ b/sysdeps/powerpc/powerpc64/le/power10/rawmemchr.S
@@ -0,0 +1,22 @@
+/* Optimized rawmemchr 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>
+
+#define USE_AS_RAWMEMCHR 1
+#include <sysdeps/powerpc/powerpc64/le/power10/strlen.S>
diff --git a/sysdeps/powerpc/powerpc64/le/power10/strlen.S b/sysdeps/powerpc/powerpc64/le/power10/strlen.S
index ca7e9eb3d8..dda5282f1b 100644
--- a/sysdeps/powerpc/powerpc64/le/power10/strlen.S
+++ b/sysdeps/powerpc/powerpc64/le/power10/strlen.S
@@ -18,10 +18,50 @@
 
 #include <sysdep.h>
 
-#ifndef STRLEN
-# define STRLEN __strlen
-# define DEFINE_STRLEN_HIDDEN_DEF 1
-#endif
+/* To reuse the code for rawmemchr, we have some extra steps compared to the
+   strlen implementation:
+      - Sum the initial value of r3 with the position at which the char was
+        found, to guarantee we return a pointer and not the length.
+      - In the main loop, subtract each byte by the char we are looking for,
+        so we can keep using vminub to quickly check 64B at once.  */
+#ifdef USE_AS_RAWMEMCHR
+# ifndef RAWMEMCHR
+#  define FUNCNAME __rawmemchr
+# else
+#  define FUNCNAME RAWMEMCHR
+# endif
+# define MCOUNT_NARGS 2
+# define VREG_ZERO v20
+# define OFF_START_LOOP 256
+# define RAWMEMCHR_SUBTRACT_VECTORS \
+	vsububm   v4,v4,v18;	    \
+	vsububm   v5,v5,v18;	    \
+	vsububm   v6,v6,v18;	    \
+	vsububm   v7,v7,v18;
+# define TAIL(vreg,increment)	   \
+	vctzlsbb  r4,vreg;	   \
+	addi	  r4,r4,increment; \
+	add	  r3,r5,r4;	   \
+	blr
+
+#else /* strlen */
+
+# ifndef STRLEN
+#  define FUNCNAME __strlen
+#  define DEFINE_STRLEN_HIDDEN_DEF 1
+# else
+#  define FUNCNAME STRLEN
+# endif
+# define MCOUNT_NARGS 1
+# define VREG_ZERO v18
+# define OFF_START_LOOP 192
+# define TAIL(vreg,increment)	   \
+	vctzlsbb  r4,vreg;	   \
+	subf	  r3,r3,r5;	   \
+	addi	  r4,r4,increment; \
+	add	  r3,r3,r4;	   \
+	blr
+#endif /* USE_AS_RAWMEMCHR */
 
 /* TODO: Replace macros by the actual instructions when minimum binutils becomes
    >= 2.35.  This is used to keep compatibility with older versions.  */
@@ -50,33 +90,41 @@
 	li	  r6,offset;		    \
 	LXVP(v4+32,offset,addr);	    \
 	LXVP(v6+32,offset+32,addr);	    \
+	RAWMEMCHR_SUBTRACT_VECTORS;	    \
 	vminub	  v14,v4,v5;		    \
 	vminub	  v15,v6,v7;		    \
 	vminub	  v16,v14,v15;		    \
-	vcmpequb. v0,v16,v18;		    \
+	vcmpequb. v0,v16,VREG_ZERO;	    \
 	bne	  cr6,L(label)
 
-#define TAIL(vreg,increment)	   \
-	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])
 
+   but when USE_AS_RAWMEMCHR is set, implements the function
+
+   void* [r3] rawmemchr (const void *s [r3], int c [r4])
+
    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
+ENTRY_TOCLESS (FUNCNAME, 4)
+	CALL_MCOUNT MCOUNT_NARGS
 
-	vspltisb  v18,0
+#ifdef USE_AS_RAWMEMCHR
+	xori	r5,r4,0xff
+
+	mtvsrd	v18+32,r4	/* matching char in v18  */
+	mtvsrd	v19+32,r5	/* non matching char in v19  */
+
+	vspltb	v18,v18,7	/* replicate  */
+	vspltb	v19,v19,7	/* replicate  */
+#else
 	vspltisb  v19,-1
+#endif
+	vspltisb  VREG_ZERO,0
 
 	/* Next 16B-aligned address. Prepare address for L(aligned).  */
 	addi	  r5,r3,16
@@ -90,16 +138,25 @@ ENTRY_TOCLESS (STRLEN, 4)
 	vcmpequb. v6,v0,v18
 	beq	  cr6,L(aligned)
 
+#ifdef USE_AS_RAWMEMCHR
+	vctzlsbb  r6,v6
+	add	  r3,r3,r6
+#else
 	vctzlsbb  r3,v6
+#endif
 	blr
 
-	/* Test next 176B, 16B at a time.  The main loop is optimized for longer
-	   strings, so checking the first bytes in 16B chunks benefits a lot
-	   small strings.  */
+	/* Test up to OFF_START_LOOP-16 bytes in 16B chunks.  The main loop is
+	   optimized for longer strings, so checking the first bytes in 16B
+	   chunks benefits a lot small strings.  */
 	.p2align 5
 L(aligned):
+#ifdef USE_AS_RAWMEMCHR
+	cmpdi	cr5,r4,0	/* Check if c == 0.  This will be useful to
+				  choose how we will perform the main loop.  */
+#endif
 	/* Prepare address for the loop.  */
-	addi	  r4,r3,192
+	addi	  r4,r3,OFF_START_LOOP
 	clrrdi	  r4,r4,6
 
 	CHECK16(v0,0,r5,tail1)
@@ -113,15 +170,43 @@ L(aligned):
 	CHECK16(v8,128,r5,tail9)
 	CHECK16(v9,144,r5,tail10)
 	CHECK16(v10,160,r5,tail11)
+#ifdef USE_AS_RAWMEMCHR
+	CHECK16(v0,176,r5,tail12)
+	CHECK16(v1,192,r5,tail13)
+	CHECK16(v2,208,r5,tail14)
+	CHECK16(v3,224,r5,tail15)
+#endif
 
 	addi	  r5,r4,128
 
+#ifdef USE_AS_RAWMEMCHR
+	/* If c == 0, use the same loop as strlen, without the vsububm.  */
+	beq	cr5,L(loop)
+
+	/* This is very similar to the block after L(loop), the difference is
+	   that here RAWMEMCHR_SUBTRACT_VECTORS is not empty, and we subtract
+	   each byte loaded by the char we are looking for, this way we can keep
+	   using vminub to merge the results and checking for nulls.  */
+	.p2align 5
+L(rawmemchr_loop):
+	CHECK64(0,r4,pre_tail_64b)
+	CHECK64(64,r4,pre_tail_64b)
+	addi	  r4,r4,256
+
+	CHECK64(0,r5,tail_64b)
+	CHECK64(64,r5,tail_64b)
+	addi	  r5,r5,256
+
+	b	  L(rawmemchr_loop)
+#endif
 	/* Switch to a more aggressive approach checking 64B each time.  Use 2
 	   pointers 128B apart and unroll the loop once to make the pointer
 	   updates and usages separated enough to avoid stalls waiting for
 	   address calculation.  */
 	.p2align 5
 L(loop):
+#undef RAWMEMCHR_SUBTRACT_VECTORS
+#define RAWMEMCHR_SUBTRACT_VECTORS /* nothing */
 	CHECK64(0,r4,pre_tail_64b)
 	CHECK64(64,r4,pre_tail_64b)
 	addi	  r4,r4,256
@@ -140,10 +225,10 @@ L(tail_64b):
 	   block and mark it in its corresponding VR.  lxvp vx,0(ry) puts the
 	   low 16B bytes into vx+1, and the high into vx, so the order here is
 	   v5, v4, v7, v6.  */
-	vcmpequb  v1,v5,v18
-	vcmpequb  v2,v4,v18
-	vcmpequb  v3,v7,v18
-	vcmpequb  v4,v6,v18
+	vcmpequb  v1,v5,VREG_ZERO
+	vcmpequb  v2,v4,VREG_ZERO
+	vcmpequb  v3,v7,VREG_ZERO
+	vcmpequb  v4,v6,VREG_ZERO
 
 	/* Take into account the other 64B blocks we had already checked.  */
 	add	r5,r5,r6
@@ -165,7 +250,9 @@ L(tail_64b):
 	or	  r10,r8,r7
 
 	cnttzd	  r0,r10	  /* Count trailing zeros before the match.  */
+#ifndef USE_AS_RAWMEMCHR
 	subf	  r5,r3,r5
+#endif
 	add	  r3,r5,r0	  /* Compute final length.  */
 	blr
 
@@ -213,9 +300,32 @@ L(tail10):
 L(tail11):
 	TAIL(v10,160)
 
-END (STRLEN)
+#ifdef USE_AS_RAWMEMCHR
+	.p2align  5
+L(tail12):
+	TAIL(v0,176)
+
+	.p2align  5
+L(tail13):
+	TAIL(v1,192)
+
+	.p2align  5
+L(tail14):
+	TAIL(v2,208)
+
+	.p2align  5
+L(tail15):
+	TAIL(v3,224)
+#endif
+
+END (FUNCNAME)
 
-#ifdef DEFINE_STRLEN_HIDDEN_DEF
+#ifdef USE_AS_RAWMEMCHR
+weak_alias (__rawmemchr,rawmemchr)
+libc_hidden_builtin_def (__rawmemchr)
+#else
+# ifdef DEFINE_STRLEN_HIDDEN_DEF
 weak_alias (__strlen, strlen)
 libc_hidden_builtin_def (strlen)
+# endif
 #endif