This is the mail archive of the libc-alpha@sourceware.org mailing list for the glibc project.


Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]
Other format: [Raw text]

[PATCH] powerpc: Optimized strcmp for POWER8/PPC64


This patch adds an optimized POWER8 strcmp using unaligned accesses.
The algorithm first check the initial 16 bytes, then align the first
function source and uses unaligned loads on second argument only.
Aditional checks for page boundaries are done for unaligned cases
(where sources alignment are different).

For unaligned cases I also tried a different approach by align
the second source argument to double and issuing aligned loads
plus internal shift/mask to isolate the bytes to compare with.
However due the additional controls and compares (one for each
splits doubleword read), I didn't see improvements over the
strategy uses on this patch.  Also, the alignment check is 
simples, resulting in a shorter code.

Tested on powerpc64 and powerpc64le.

--

 	* sysdeps/powerpc/powerpc64/multiarch/Makefile [sysdep_routines]:
	Add strcmp-power8 object.
	* sysdeps/powerpc/powerpc64/multiarch/ifunc-impl-list.c
	(__libc_ifunc_impl_list): Add __strcmp_power8 implementation.
	* sysdeps/powerpc/powerpc64/multiarch/strcmp-power8.S: New file.
	* sysdeps/powerpc/powerpc64/multiarch/strcmp.c (strcmp): Add
	__strcmp_power8 implementation.
	* sysdeps/powerpc/powerpc64/power8/strcmp.S: New file.
	* NEWS: Update.

--

diff --git a/ChangeLog b/ChangeLog
index 5f0b4ea..e71bba3 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,6 +1,16 @@
 2015-01-07  Adhemerval Zanella  <azanella@linux.vnet.ibm.com>
 
 	* sysdeps/powerpc/powerpc64/multiarch/Makefile [sysdep_routines]:
+	Add strcmp-power8 object.
+	* sysdeps/powerpc/powerpc64/multiarch/ifunc-impl-list.c
+	(__libc_ifunc_impl_list): Add __strcmp_power8 implementation.
+	* sysdeps/powerpc/powerpc64/multiarch/strcmp-power8.S: New file.
+	* sysdeps/powerpc/powerpc64/multiarch/strcmp.c (strcmp): Add
+	__strcmp_power8 implementation.
+	* sysdeps/powerpc/powerpc64/power8/strcmp.S: New file.
+	* NEWS: Update.
+
+	* sysdeps/powerpc/powerpc64/multiarch/Makefile [sysdep_routines]:
 	Add strncpy-power8 and stpncpy-power8 objects.
 	* sysdeps/powerpc/powerpc64/multiarch/ifunc-impl-list.c
 	(__libc_ifunc_impl_list): Add __strncpy_power8 and stpncpy_power8
diff --git a/NEWS b/NEWS
index 975b675..ebcdb3a 100644
--- a/NEWS
+++ b/NEWS
@@ -19,6 +19,9 @@ Version 2.21
   17744, 17745, 17746, 17747, 17775, 17777, 17780, 17781, 17782, 17793,
   17796, 17797, 17806
 
+* Optimized strcmp implementation for powerpc64/powerpc64le.
+  Implemented by Adhemerval Zanella..
+
 * Optimized strcpy, stpcpy, strchrnul and strrchr implementations for
   AArch64.  Contributed by ARM Ltd.
 
diff --git a/sysdeps/powerpc/powerpc64/multiarch/Makefile b/sysdeps/powerpc/powerpc64/multiarch/Makefile
index 18d3378..ec4fca7 100644
--- a/sysdeps/powerpc/powerpc64/multiarch/Makefile
+++ b/sysdeps/powerpc/powerpc64/multiarch/Makefile
@@ -18,7 +18,7 @@ sysdep_routines += memcpy-power7 memcpy-a2 memcpy-power6 memcpy-cell \
 		   strrchr-power7 strrchr-ppc64 strncat-power7 strncat-ppc64 \
 		   strncpy-power7 strncpy-ppc64 \
 		   stpncpy-power8 stpncpy-power7 stpncpy-ppc64 \
-		   strcmp-power7 strcmp-ppc64 \
+		   strcmp-power8 strcmp-power7 strcmp-ppc64 \
 		   strcat-power8 strcat-power7 strcat-ppc64 memmove-power7 \
 		   memmove-ppc64 bcopy-ppc64 strncpy-power8
 
diff --git a/sysdeps/powerpc/powerpc64/multiarch/ifunc-impl-list.c b/sysdeps/powerpc/powerpc64/multiarch/ifunc-impl-list.c
index 132cb13..2c03060 100644
--- a/sysdeps/powerpc/powerpc64/multiarch/ifunc-impl-list.c
+++ b/sysdeps/powerpc/powerpc64/multiarch/ifunc-impl-list.c
@@ -301,6 +301,9 @@ __libc_ifunc_impl_list (const char *name, struct libc_ifunc_impl *array,
   /* Support sysdeps/powerpc/powerpc64/multiarch/strcmp.c.  */
   IFUNC_IMPL (i, name, strcmp,
 	      IFUNC_IMPL_ADD (array, i, strcmp,
+			      hwcap2 & PPC_FEATURE2_ARCH_2_07,
+			      __strcmp_power8)
+	      IFUNC_IMPL_ADD (array, i, strcmp,
 			      hwcap & PPC_FEATURE_HAS_VSX,
 			      __strcmp_power7)
 	      IFUNC_IMPL_ADD (array, i, strcmp, 1,
diff --git a/sysdeps/powerpc/powerpc64/multiarch/strcmp-power8.S b/sysdeps/powerpc/powerpc64/multiarch/strcmp-power8.S
new file mode 100644
index 0000000..899692b
--- /dev/null
+++ b/sysdeps/powerpc/powerpc64/multiarch/strcmp-power8.S
@@ -0,0 +1,40 @@
+/* Optimized strcmp implementation for POWER8/PPC64.
+   Copyright (C) 2014-2015 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
+   <http://www.gnu.org/licenses/>.  */
+
+#include <sysdep.h>
+
+#undef EALIGN
+#define EALIGN(name, alignt, words)				\
+  .section ".text";						\
+  ENTRY_2(__strcmp_power8)					\
+  .align ALIGNARG(alignt);					\
+  EALIGN_W_##words;						\
+  BODY_LABEL(__strcmp_power8):					\
+  cfi_startproc;						\
+  LOCALENTRY(__strcmp_power8)
+
+#undef END
+#define END(name)						\
+  cfi_endproc;							\
+  TRACEBACK(__strcmp_power8)					\
+  END_2(__strcmp_power8)
+
+#undef libc_hidden_builtin_def
+#define libc_hidden_builtin_def(name)
+
+#include <sysdeps/powerpc/powerpc64/power8/strcmp.S>
diff --git a/sysdeps/powerpc/powerpc64/multiarch/strcmp.c b/sysdeps/powerpc/powerpc64/multiarch/strcmp.c
index 9b2922f..b45ba1f 100644
--- a/sysdeps/powerpc/powerpc64/multiarch/strcmp.c
+++ b/sysdeps/powerpc/powerpc64/multiarch/strcmp.c
@@ -23,9 +23,12 @@
 
 extern __typeof (strcmp) __strcmp_ppc attribute_hidden;
 extern __typeof (strcmp) __strcmp_power7 attribute_hidden;
+extern __typeof (strcmp) __strcmp_power8 attribute_hidden;
 
 libc_ifunc (strcmp,
-            (hwcap & PPC_FEATURE_HAS_VSX)
-            ? __strcmp_power7
+            (hwcap2 & PPC_FEATURE2_ARCH_2_07)
+              ? __strcmp_power8 :
+              (hwcap & PPC_FEATURE_HAS_VSX)
+              ? __strcmp_power7
             : __strcmp_ppc);
 #endif
diff --git a/sysdeps/powerpc/powerpc64/power8/strcmp.S b/sysdeps/powerpc/powerpc64/power8/strcmp.S
new file mode 100644
index 0000000..cdad1eb
--- /dev/null
+++ b/sysdeps/powerpc/powerpc64/power8/strcmp.S
@@ -0,0 +1,263 @@
+/* Optimized strcmp implementation for PowerPC64/POWER8.
+   Copyright (C) 2015 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
+   <http://www.gnu.org/licenses/>.  */
+
+#include <sysdep.h>
+
+/* Implements the function
+
+   size_t [r3] strcmp (const char *s1 [r3], const char *s2 [r4])
+
+   The implementation uses unaligned doubleword access to avoid specialized
+   code paths depending of data alignment.  Although recent powerpc64 uses
+   64K as default, the page cross handling assumes minimum page size of
+   4k.  */
+
+EALIGN (strcmp, 4, 0)
+	/* Check if [s1]+15 or [s2]+15 will cross a 4K page boundary using
+	   the code:
+
+	    (((size_t) s1) % PAGE_SIZE > (PAGE_SIZE - ITER_SIZE))
+
+	   with PAGE_SIZE being 4096 and ITER_SIZE begin 16.  */
+
+	rldicl	r7,r3,0,52
+	rldicl	r9,r4,0,52
+	cmpldi	cr7,r7,4080
+	bgt	cr7,L(pagecross_check)
+	cmpldi	cr7,r9,4080
+	bgt	cr7,L(pagecross_check)
+
+	/* For short string up to 16 bytes, load both s1 and s2 using
+	   unaligned dwords and compare.  */
+	ld	r8,0(r3)
+	ld	r10,0(r4)
+	li	r9,0
+	cmpb	r7,r8,r9
+	cmpdi	cr7,r7,0
+	mr	r9,r7
+	bne 	cr7,L(null_found)
+	cmpld	cr7,r8,r10
+	bne	cr7,L(different)
+	ld	r8,8(r3)
+	ld	r10,8(r4)
+	cmpb	r9,r8,r7
+	cmpdi	cr7,r9,r0
+	bne	cr7,L(null_found)
+	cmpld	cr7,r8,r10
+	bne	cr7,L(different)
+	addi	r7,r3,16
+	addi	r4,r4,16
+	b	L(align_16b)
+
+	/* A zero byte was found in r8 (s1 dword), r9 contains the cmpb
+	   result and r10 the dword from s2.  To code isolate the byte
+	   up to end (including the '\0'), masking with 0xFF the remaining
+	   ones:
+
+           #if __LITTLE_ENDIAN__
+	     (__builtin_ffsl (x) - 1) = counting trailing zero bits
+	     r9 = (__builtin_ffsl (r9) - 1) + 8;
+	     r9 = -1UL << r9
+	   #else
+	     r9  = __builtin_clzl (r9) + 8;
+	     r9  = -1UL >> r9
+	   #endif
+	     r8  = r8  | r9
+	     r10 = r10 | r9  */
+L(null_found):
+#ifdef __LITTLE_ENDIAN__
+	neg	r7,r9
+	and	r9,r9,r7
+	li	r7,-1
+	cntlzd	r9,r9
+	subfic	r9,r9,71
+	sld	r9,r7,r9
+#else
+	cntlzd	r9,r9
+	li	r7,-1
+	addi	r9,r9,8
+	srd	r9,r7,r9
+#endif
+	or	r8,r8,r9
+	or	r10,r10,r9
+
+	/* The code now check if r8 and r10 are different by issuing a
+	   cmpb and shift the result based on its output:
+
+	     r9  = ~ (cmpb (r8, r10));
+	   #ifdef __LITTLE_ENDIAN__
+	     r9 = (__builtin_ffsl (r9) - 1);
+	   #else
+	     r9  = __builtin_clzl (r9);
+	   #endif
+	     r10 = (r10 >> (56 - r9)) & 0xFF;
+	     r3  = ( r8 >> (56 - r9)) & 0xFF;
+	     return r3 - r10  */
+L(different):
+	cmpb	r9,r8,r10
+#ifdef __LITTLE_ENDIAN__
+	addi	r7,r9,1
+	andc	r9,r7,r9
+	cntlzd	r9,r9
+	subfic	r9,r9,63
+#else
+	not	r9,r9
+	cntlzd	r9,r9
+	subfic	r9,r9,56
+#endif
+	srd	r3,r8,r9
+	srd	r10,r10,r9
+	rldicl	r10,r10,0,56
+	rldicl	r3,r3,0,56
+	subf	r3,r10,r3
+	blr
+
+	.align	4
+L(align_16b):
+	/* Now it has checked for first 16 bytes, align source1 to doubleword
+	   and adjust source2 address.  */
+	rldicl	r9,r7,0,61	/* source1 alignment to doubleword  */
+	li	r6,0
+	subf	r4,r9,r4	/* Adjust source2 address based on source1
+				   alignment.  */
+	rldicr	r7,r7,0,60	/* Align source1 to doubleword.  */
+
+	/* At this point, source1 alignment is 0 and source2 alignment is
+	   between 0 and 7.  Check is source2 alignment is 0, meaning both
+	   sources have the same alignment.  */
+	andi.	r9,r4,0x7
+	bne	cr0,L(loop_diff_align)
+
+	/* If both source1 and source2 are doubleword aligned, there is no
+	   need for page boundary cross checks.  */
+	ld	r8,0(r7)
+	ld	r10,0(r4)
+	cmpb	r9,r8,r9
+	cmpdi	cr7,r9,0
+	bne	cr7,L(null_found)
+	cmpld	cr7,r10,r8
+	bne	cr7,L(different)
+	li	r6,0
+	b	L(loop_equal_align)
+
+	.align	4
+L(loop_equal_align_0):
+	bne	cr5,L(different)
+L(loop_equal_align):
+	ldu	r8,8(7)
+	ldu	r10,8(4)
+	cmpb	r9,r8,r6
+	cmpdi	cr7,r9,0
+	cmpld	cr5,r8,r10
+	beq	cr7,L(loop_equal_align_0)
+	b	L(null_found)
+
+	.align	4
+L(pagecross_check):
+	subfic	r9,r9,4096
+	subfic	r7,r7,4096
+	cmpld	cr7,r7,r9
+	bge	cr7,L(pagecross)
+	mr	r7,r9
+
+	/* If unaligned 16 bytes reads across a 4K page boundary, it uses
+	   a simple byte a byte comparison until the page alignment for s1
+	   is reached.  */
+L(pagecross):
+	add	r7,r3,r7
+	subf	r9,r3,r7
+	mtctr	r9
+
+	.align	4
+L(pagecross_loop):
+	/* Loads a byte from s1 and s2, compare if *s1 is equal to *s2
+	   and if *s1 is '\0'.  */
+	lbz	r9,0(r3)
+	lbz	r10,0(r4)
+	addi	r3,r3,1
+	addi	r4,r4,1
+	cmplw	cr7,r9,r10
+	cmpdi	cr5,r9,r0
+	bne	cr7,L(pagecross_ne)
+	beq	cr5,L(pagecross_nullfound)
+	bdnz	L(pagecross_loop)
+	b	L(align_16b)
+
+	.align	4
+	/* The unaligned read of source2 will cross a 4K page boundary,
+	   and the different byte or NULL maybe be in the remaining page
+	   bytes.  In this since, since it can not use the unaligned
+	   load the algorithm reads and compares 8 bytes to keep source1
+	   doubleword aligned.  */
+L(check_source2_byte):
+	li	r9,8
+	mtctr	r9
+
+	.align	4
+L(check_source2_byte_loop):
+	lbz	r9,0(r7)
+	lbz	r10,0(r4)
+	addi	r7,r7,1
+	addi	r4,r4,1
+	cmplw	cr7,r9,10
+	cmpdi	r5,r9,0
+	bne	cr7,L(pagecross_ne)
+	beq	cr5,L(pagecross_nullfound)
+	bdnz	L(check_source2_byte_loop)
+
+	/* If source2 is unaligned to doubleword, the code needs to check
+	   on each interation if the unaligned doubleword access will cross
+	   a 4k page boundary.  */
+	.align	4
+L(loop_unaligned):
+	ld	r8,0(r7)
+	ld	r10,0(r4)
+	cmpb	r9,r8,r6
+	cmpdi	cr7,r9,0
+	bne	cr7,L(null_found)
+	cmpld	cr7,r8,r10
+	bne	cr7,L(different)
+	addi	r7,r7,8
+	addi	r4,r4,8
+
+L(loop_diff_align):
+	/* Check if [src2]+8 cross a 4k page boundary:
+
+	     srcin2 % PAGE_SIZE > (PAGE_SIZE - 8)
+
+	     with PAGE_SIZE being 4096.  */
+	rldicl	r9,r4,0,52
+	cmpldi	cr7,r9,4088
+	ble	cr7,L(loop_unaligned)
+	b	L(check_source2_byte)
+
+	.align	4
+L(pagecross_ne):
+	extsw	r3,r9
+	mr	r9,r10
+L(pagecross_retdiff):
+	subf	r9,r9,r3
+	extsw	r3,r9
+	blr
+
+	.align	4
+L(pagecross_nullfound):
+	li	r3,0
+	b	L(pagecross_retdiff)
+END (strcmp)
+libc_hidden_builtin_def (strcmp)


Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]