POWER9 DD2.1 and earlier has an issue where some cache inhibited
vector load traps to the kernel, causing a performance degradation. To
handle this in memcpy and memmove, lvx/stvx is used for aligned
addresses instead of lxvd2x/stxvd2x.
Reference: https://patchwork.ozlabs.org/patch/814059/
* sysdeps/powerpc/powerpc64/power7/memcpy.S: Replace
lxvd2x/stxvd2x with lvx/stvx.
* sysdeps/powerpc/powerpc64/power7/memmove.S: Likewise.
Reviewed-by: Tulio Magno Quites Machado Filho <tuliom@linux.vnet.ibm.com>
Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
(cherry picked from commit 63da5cd4a0)
<locale.h> is specified to define locale_t in POSIX.1-2008, and so are
all of the headers that define functions that take locale_t arguments.
Under _GNU_SOURCE, the additional headers that define such functions
have also always defined locale_t. Therefore, there is no need to use
__locale_t in public function prototypes, nor in any internal code.
* ctype/ctype-c99_l.c, ctype/ctype.h, ctype/ctype_l.c
* include/monetary.h, include/stdlib.h, include/time.h
* include/wchar.h, locale/duplocale.c, locale/freelocale.c
* locale/global-locale.c, locale/langinfo.h, locale/locale.h
* locale/localeinfo.h, locale/newlocale.c
* locale/nl_langinfo_l.c, locale/uselocale.c
* localedata/bug-usesetlocale.c, localedata/tst-xlocale2.c
* stdio-common/vfscanf.c, stdlib/monetary.h, stdlib/stdlib.h
* stdlib/strfmon_l.c, stdlib/strtod_l.c, stdlib/strtof_l.c
* stdlib/strtol.c, stdlib/strtol_l.c, stdlib/strtold_l.c
* stdlib/strtoll_l.c, stdlib/strtoul_l.c, stdlib/strtoull_l.c
* string/strcasecmp.c, string/strcoll_l.c, string/string.h
* string/strings.h, string/strncase.c, string/strxfrm_l.c
* sysdeps/ieee754/float128/strtof128_l.c
* sysdeps/ieee754/float128/wcstof128.c
* sysdeps/ieee754/float128/wcstof128_l.c
* sysdeps/ieee754/ldbl-128ibm/strtold_l.c
* sysdeps/ieee754/ldbl-64-128/strtold_l.c
* sysdeps/ieee754/ldbl-opt/nldbl-compat.c
* sysdeps/ieee754/ldbl-opt/nldbl-strfmon_l.c
* sysdeps/ieee754/ldbl-opt/nldbl-strtold_l.c
* sysdeps/ieee754/ldbl-opt/nldbl-wcstold_l.c
* sysdeps/powerpc/powerpc32/power7/strcasecmp.S
* sysdeps/powerpc/powerpc64/power7/strcasecmp.S
* sysdeps/x86_64/strcasecmp_l-nonascii.c
* sysdeps/x86_64/strncase_l-nonascii.c, time/strftime_l.c
* time/strptime_l.c, time/time.h, wcsmbs/mbsrtowcs_l.c
* wcsmbs/wchar.h, wcsmbs/wcscasecmp.c, wcsmbs/wcsncase.c
* wcsmbs/wcstod.c, wcsmbs/wcstod_l.c, wcsmbs/wcstof.c
* wcsmbs/wcstof_l.c, wcsmbs/wcstol_l.c, wcsmbs/wcstold.c
* wcsmbs/wcstold_l.c, wcsmbs/wcstoll_l.c, wcsmbs/wcstoul_l.c
* wcsmbs/wcstoull_l.c, wctype/iswctype_l.c
* wctype/towctrans_l.c, wctype/wcfuncs_l.c
* wctype/wctrans_l.c, wctype/wctype.h, wctype/wctype_l.c:
Change all uses of __locale_t to locale_t.
Makes __stpncpy_power8 call __memset_power8 directly rather than via an
IFUNC. Fixes a missing _mcount, and removes some redundant NOPS. The
*_is_local defines are also used in a followup patch.
* sysdeps/powerpc/powerpc64/multiarch/strncpy-power7.S: Define
MEMSET_is_local.
* sysdeps/powerpc/powerpc64/multiarch/strncpy-power8.S: Likewise.
* sysdeps/powerpc/powerpc64/multiarch/stpncpy-power7.S: Likewise.
* sysdeps/powerpc/powerpc64/multiarch/stpncpy-power8.S: Likewise.
Define MEMSET.
* sysdeps/powerpc/powerpc64/multiarch/strstr-power7.S: Define
STRLEN_is_local, STRNLEN_is_local, and STRCHR_is_local.
* sysdeps/powerpc/powerpc64/power7/strstr.S: Likewise. Don't add
nop after local calls.
* sysdeps/powerpc/powerpc64/power7/strncpy.S: Define MEMSET_is_local.
Don't add nop after local call.
* sysdeps/powerpc/powerpc64/power8/strncpy.S: Likewise. Add missing
CALL_MCOUNT.
Clean up the IFUNC implementations for powerpc in order to remove
unneeded macro definitions.
Tested on ppc64le with and without --disable-multi-arch flag.
* sysdeps/powerpc/powerpc64/multiarch/memcmp-power4.S: Define the
implementation-specific function name and remove unneeded
macros definition.
* sysdeps/powerpc/powerpc64/multiarch/memcmp-power7.S: Likewise.
* sysdeps/powerpc/powerpc64/multiarch/memmove-power7.S: Likewise.
* sysdeps/powerpc/powerpc64/power4/memcmp.S: Set a default function
name if not defined and pass as parameter to macros accordingly.
* sysdeps/powerpc/powerpc64/power7/memcmp.S: Likewise.
* sysdeps/powerpc/powerpc64/power7/memmove.S: Likewise.
Clean up the IFUNC implementations for powerpc in order to remove
unneeded macro definitions.
Tested on ppc64le with and without --disable-multi-arch flag.
* sysdeps/powerpc/powerpc64/multiarch/memcpy-a2.S: Define the
implementation-specific function name and remove unneeded
macros definition.
* sysdeps/powerpc/powerpc64/multiarch/memcpy-cell.S: Likewise.
* sysdeps/powerpc/powerpc64/multiarch/memcpy-power4.S: Likewise.
* sysdeps/powerpc/powerpc64/multiarch/memcpy-power6.S: Likewise.
* sysdeps/powerpc/powerpc64/multiarch/memcpy-power7.S: Likewise.
* sysdeps/powerpc/powerpc64/multiarch/memcpy-ppc64.S: Likewise.
* sysdeps/powerpc/powerpc64/multiarch/mempcpy-power7.S: Likewise.
* sysdeps/powerpc/powerpc64/a2/memcpy.S: Set a default function
name if not defined and pass as parameter to macros accordingly.
* sysdeps/powerpc/powerpc64/cell/memcpy.S: Likewise.
* sysdeps/powerpc/powerpc64/memcpy.S: Likewise.
* sysdeps/powerpc/powerpc64/power4/memcpy.S: Likewise.
* sysdeps/powerpc/powerpc64/power6/memcpy.S: Likewise.
* sysdeps/powerpc/powerpc64/power7/memcpy.S: Likewise.
* sysdeps/powerpc/powerpc64/power7/mempcpy.S: Likewise.
Clean up the IFUNC implementations for powerpc in order to remove
unneeded macro definitions.
Tested on ppc64le with and without --disable-multi-arch flag.
* sysdeps/powerpc/powerpc64/multiarch/memchr-power7.S: Define the
implementation-specific function name and remove unneeded macros
definition.
* sysdeps/powerpc/powerpc64/multiarch/memrchr-power7.S: Likewise.
* sysdeps/powerpc/powerpc64/multiarch/rawmemchr-power7.S: Likewise.
* sysdeps/powerpc/powerpc64/power7/memchr.S: Set a default
function name if not defined and pass as parameter to macros
accordingly.
* sysdeps/powerpc/powerpc64/power7/memrchr.S: Likewise.
* sysdeps/powerpc/powerpc64/power7/rawmemchr.S: Likewise.
Clean up the IFUNC implementations for powerpc in order to remove
unneeded macro definitions.
Tested on ppc64le with and without --disable-multi-arch flag.
* sysdeps/powerpc/powerpc64/multiarch/memset-power4.S: Define the
implementation-specific function name and remove unneeded macros
definition.
* sysdeps/powerpc/powerpc64/multiarch/memset-power6.S: Likewise.
* sysdeps/powerpc/powerpc64/multiarch/memset-power7.S: Likewise.
* sysdeps/powerpc/powerpc64/multiarch/memset-power8.S: Likewise.
* sysdeps/powerpc/powerpc64/multiarch/memset-ppc64.S: Likewise.
* sysdeps/powerpc/powerpc64/memset.S: Set a default function name if
not defined and pass as parameter to macros accordingly.
* sysdeps/powerpc/powerpc64/power4/memset.S: Likewise.
* sysdeps/powerpc/powerpc64/power6/memset.S: Likewise.
* sysdeps/powerpc/powerpc64/power7/memset.S: Likewise.
* sysdeps/powerpc/powerpc64/power8/memset.S: Likewise.
Clean up the IFUNC implementations for powerpc in order to remove
unneeded macro definitions.
Tested on ppc64le with and without --disable-multi-arch flag.
* sysdeps/powerpc/powerpc64/multiarch/strcasestr-power8.S: Define the
strcasestr implementation name and remove unneeded macros definition.
* sysdeps/powerpc/powerpc64/multiarch/strstr-power7.S: Define
strstr implementation name and remove unneeded macros definition.
* sysdeps/powerpc/powerpc64/power7/strstr.S: Set a default function
name if not defined and pass as parameter to macros accordingly.
* sysdeps/powerpc/powerpc64/power8/strcasestr.S: Likewise.
Clean up the IFUNC implementations for powerpc in order to remove
unneeded macro definitions.
Tested on ppc64le with and without --disable-multi-arch flag.
* sysdeps/powerpc/powerpc64/multiarch/strchr-power7.S: Define the
implementation-specific function name and remove unneeded macros
definition.
* sysdeps/powerpc/powerpc64/multiarch/strchr-power8.S: Likewise.
* sysdeps/powerpc/powerpc64/multiarch/strchr-ppc64.S: Likewise.
* sysdeps/powerpc/powerpc64/multiarch/strchrnul-power7.S: Likewise.
* sysdeps/powerpc/powerpc64/multiarch/strchrnul-power8.S: Likewise.
* sysdeps/powerpc/powerpc64/multiarch/strrchr-power7.S: Likewise.
* sysdeps/powerpc/powerpc64/power7/strchr.S: Set a default
function name if not defined and pass as parameter to macros
accordingly.
* sysdeps/powerpc/powerpc64/power7/strchrnul.S: Likewise.
* sysdeps/powerpc/powerpc64/power7/strrchr.S: Likewise.
* sysdeps/powerpc/powerpc64/power8/strchr.S: Likewise.
* sysdeps/powerpc/powerpc64/strchr.S: Likewise.
Clean up the IFUNC implementations for powerpc in order to remove
unneeded macro definitions.
Tested on ppc64le with and without --disable-multi-arch flag.
* sysdeps/powerpc/powerpc64/multiarch/strlen-power7.S: Define
the strlen implementation name and remove unneeded macros definition.
* sysdeps/powerpc/powerpc64/multiarch/strlen-power8.S: Likewise.
* sysdeps/powerpc/powerpc64/multiarch/strlen-ppc64.S: Likewise.
* sysdeps/powerpc/powerpc64/multiarch/strnlen-power7.S: Define
the strnlen implementation name and remove unneeded macros definition.
* sysdeps/powerpc/powerpc64/power7/strlen.S: Set a default function
name if not defined and pass as parameter to macros accordingly.
* sysdeps/powerpc/powerpc64/power7/strnlen.S: Likewise.
* sysdeps/powerpc/powerpc64/power8/strlen.S: Likewise.
* sysdeps/powerpc/powerpc64/strlen.S: Likewise.
Clean up the IFUNC implementations for powerpc in order to remove
unneeded macro definitions.
Tested on ppc64le with and without --disable-multi-arch flag.
* sysdeps/powerpc/powerpc64/multiarch/strcasecmp_l-power7.S: Define
the implementation-specific function name and remove unneeded
macros definition.
* sysdeps/powerpc/powerpc64/multiarch/strcmp-power7.S: Likewise.
* sysdeps/powerpc/powerpc64/multiarch/strcmp-power8.S Likewise.
* sysdeps/powerpc/powerpc64/multiarch/strcmp-power9.S: Likewise.
* sysdeps/powerpc/powerpc64/multiarch/strcmp-ppc64.S: Likewise.
* sysdeps/powerpc/powerpc64/multiarch/strncmp-power4.S: Likewise.
* sysdeps/powerpc/powerpc64/multiarch/strncmp-power7.S: Likewise.
* sysdeps/powerpc/powerpc64/multiarch/strncmp-power8.S: Likewise.
* sysdeps/powerpc/powerpc64/multiarch/strncmp-power9.S: Likewise.
* sysdeps/powerpc/powerpc64/multiarch/strncmp-ppc64.S: Likewise.
* sysdeps/powerpc/powerpc64/power4/strncmp.S: Set a default function
name if not defined and pass as parameter to macros accordingly.
* sysdeps/powerpc/powerpc64/power7/strcmp.S: Likewise.
* sysdeps/powerpc/powerpc64/power7/strncmp.S: Likewise.
* sysdeps/powerpc/powerpc64/power8/strcmp.S: Likewise.
* sysdeps/powerpc/powerpc64/power8/strncmp.S: Likewise.
* sysdeps/powerpc/powerpc64/power9/strcmp.S: Likewise.
* sysdeps/powerpc/powerpc64/power9/strncmp.S: Likewise.
* sysdeps/powerpc/powerpc64/strcmp.S: Likewise.
* sysdeps/powerpc/powerpc64/strncmp.S: Likewise.
Clean up the IFUNC implementations for powerpc in order to remove
unneeded macro definitions.
Tested on ppc64le with and without --disable-multi-arch flag.
* sysdeps/powerpc/powerpc64/multiarch/stpcpy-power8.S: Define the
implementation-specific function name and remove unneeded macros
definition.
* sysdeps/powerpc/powerpc64/multiarch/stpncpy-power7.S: Likewise.
* sysdeps/powerpc/powerpc64/multiarch/stpncpy-power8.S: Likewise.
* sysdeps/powerpc/powerpc64/multiarch/strcpy-power8.S: Likewise.
* sysdeps/powerpc/powerpc64/multiarch/strncpy-power7.S: Likewise.
* sysdeps/powerpc/powerpc64/multiarch/strncpy-power8.S: Likewise.
* sysdeps/powerpc/powerpc64/power7/strncpy.S: Set a default
function name if not defined.
* sysdeps/powerpc/powerpc64/power8/strcpy.S: Likewise.
* sysdeps/powerpc/powerpc64/power8/strncpy.S: Likewise.
Current optimized powercp64/power7 memchr uses a strategy to check for
p versus align(p+n) (where 'p' is the input char pointer and n the
maximum size to check for the byte) without taking care for possible
overflow on the pointer addition in case of large 'n'.
It was triggered by 3038145ca2 where default rawmemchr (used to
created ppc64 rawmemchr in ifunc selection) now uses memchr (p, c, (size_t)-1)
on its implementation.
This patch fixes it by implement a satured addition where overflows
sets the maximum pointer size to UINTPTR_MAX.
Checked on powerpc64le-linux-gnu.
[BZ# 20971]
* sysdeps/powerpc/powerpc64/power7/memchr.S (__memchr): Avoid
overflow in pointer addition.
* string/test-memchr.c (do_test): Add an argument to pass as
the size on memchr.
(test_main): Add check for SIZE_MAX.
Instead of checking needle length, constant 'n' number of comparisons
is checked to fall back to default implementation. This patch is tested
on powerpc64 and powerpc64le.
2015-08-25 Rajalakshmi Srinivasaraghavan <raji@linux.vnet.ibm.com>
* sysdeps/powerpc/powerpc64/power7/strstr.S: Handle worst case.
When building with --disable-multi-arch the memmove and strstr POWER7
optimization create and uses symbols that conflict with expect conform
tests.
* sysdeps/powerpc/powerpc64/power7/memmove.S (bcopy): Changing to
__bcopy and add a weak_alias to bcopy.
* sysdeps/powerpc/powerpc64/power7/strstr.S (strstr): Use __strnlen
for static build.
This patches uses the default strcpy/stpcpy implementation for
POWER7/PPC64. This is faster in mostly inputs for benchtests
and for multiarch the implementation uses the POWER7 strlen and
memcpy.
* string/stpcpy.c (__stpcpy): Use STPCPY to redefine symbol name and
cleanup macro usage.
* string/strcpy.c (strcpt): Use STRCPY to redefine symbol name.
* sysdeps/powerpc/powerpc64/multiarch/stpcpy-power7.S: Remove file.
* sysdeps/powerpc/powerpc64/multiarch/stpcpy-ppc64.S: Likewise.
* sysdeps/powerpc/powerpc64/multiarch/strcpy-power7.S: Likewise.
* sysdeps/powerpc/powerpc64/multiarch/strcpy-ppc64.S: Likewise.
* sysdeps/powerpc/powerpc64/power7/stpcpy.S: Likewise.
* sysdeps/powerpc/powerpc64/power7/strcpy.S: Likewise.
* sysdeps/powerpc/powerpc64/power7/strcpy.c: Likewise.
* sysdeps/powerpc/powerpc64/stpcpy.S: Likewise.
* sysdeps/powerpc/powerpc64/strcpy.S: Likewise.
* sysdeps/powerpc/powerpc64/multiarch/stpcpy.c
[SHARED && IS_IN (libc)]: Include <string/strcpy.c>.
* sysdeps/powerpc/powerpc64/multiarch/stpcpy.c
[SHARED && IS_IN (libc)]: Include <string/stpcpy.c>.
* sysdeps/powerpc/powerpc64/multiarch/stpcpy-power7.c: New file.
* sysdeps/powerpc/powerpc64/multiarch/stpcpy-ppc64.c: Likewise.
* sysdeps/powerpc/powerpc64/multiarch/strcpy-power7.c: Likewise.
* sysdeps/powerpc/powerpc64/multiarch/strcpy-ppc64.c: Likewise.
* sysdeps/powerpc/powerpc64/power7/strcpy.c: Likewise.
This patch fixes the strstr build with --disable-multi-arch option.
The optimization calls the __strstr_ppc symbol, which always build
for multiarch config but not if it is disable. This patch fixes it
by adding the default C implementation object with the expected
symbol name.
* sysdeps/powerpc/powerpc64/power7/Makefile [$(subdir) = string]
(sysdep_routines): Add strstr-ppc64.
* sysdeps/powerpc/powerpc64/power7/strstr-ppc64.c: New file.
This patch optimizes strstr function for power >= 7 systems. Performance
gain is obtained using aligned memory access and usage of cmpb
instruction for quicker comparison. The average improvement of this
optimization is ~40%. Tested on ppc64 and ppc64le.
2015-07-16 Rajalakshmi Srinivasaraghavan <raji@linux.vnet.ibm.com>
* sysdeps/powerpc/powerpc64/multiarch/Makefile: Add strstr().
* sysdeps/powerpc/powerpc64/multiarch/ifunc-impl-list.c: Likewise.
* sysdeps/powerpc/powerpc64/power7/strstr.S: New File.
* sysdeps/powerpc/powerpc64/multiarch/strstr-power7.S: New File.
* sysdeps/powerpc/powerpc64/multiarch/strstr-ppc64.c: New File.
* sysdeps/powerpc/powerpc64/multiarch/strstr.c: New File.
This patch optimizes strncpy for power7 for unaligned source or
destination address. The source or destination address is aligned
to doubleword and data is shifted based on the alignment and
added with the previous loaded data to be written as a doubleword.
For each load, cmpb instruction is used for faster null check.
The new optimization shows 10 to 70% of performance improvement
for longer string though it does not show big difference on string
size less than 16 due to additional checks.Hence this new algorithm
is restricted to string greater than 16.
This patch fixes a performance regression on the POWER7/PPC64 memcmp
porting for Little Endian. The LE code uses 'ldbrx' instruction to read
the memory on byte reversed form, however ISA 2.06 just provide the indexed
form which uses a register value as additional index, instead of a fixed value
enconded in the instruction.
And the port strategy for LE uses r0 index value and update the address
value on each compare loop interation. For large compare size values,
it adds 8 more instructions plus some more depending of trailing
size. This patch fixes it by adding pre-calculate indexes to remove the
address update on loops and tailing sizes.
For large sizes it shows a considerable gain, with double performance
pairing with BE.
This patch optimized the POWER7 trailing check by avoiding using byte
read operations and instead use the doubleword already readed with
bitwise operations.
With 3eb38795db (Simplify strncat) the generic algorithms uses
strlen, strnlen, and memcpy. This is faster than POWER7 current
implementation, especially for unaligned strings (where POWER7 code
uses byte-byte operations).
This patch removes the assembly implementation and uses a multiarch
specialization based on default algorithm calling optimized POWER7
symbols.
This patch optimizes strcpy for ppc64/power7 for unaligned source or
destination address. The source or destination address is aligned
to doubleword and data is shifted based on the alignment and
added with the previous loaded data to be written as a doubleword.
For each load, cmpb instruction is used for faster null check.
The word aligned optimization is also removed, since the new unaligned
code path shows better results handling word-aligned strings.
More combination of unaligned inputs is also added in benchtest
to measure the improvement.The new optimization shows 2 to 80% of
performance improvement for longer string though it does not show
big difference on string size less than 16 due to additional checks.
This patch makes the POWER7 optimized strpbrk generic by using
default doubleword stores to zero the hash, instead of VSX
instructions. Performance on POWER7/POWER8 does not change.
This patch makes the POWER7 optimized strcspn generic by using
default doubleword stores to zero the hash, instead of VSX
instructions. Performance on POWER7/POWER8 does not change.
This patch makes the POWER7 optimized strspn generic by using
default doubleword stores to zero the hash, instead of VSX
instructions. Performance on POWER7/POWER8 machines does not changed.
This patch cleanups the multiarch bzero for powerpc64 by remove
the multiarch objects and use instead the the memset embedded
implementation presented in each multiarch optimization. The
code generate is essentially the same, but the TB_TOCLESS (which
is not essential).
This patch changes power7 memcpy to use VSX instructions only when
memory is aligned to quardword. It is to avoid unaligned kernel traps
on non-cacheable memory (for instance, memory-mapped I/O).
This patch adds an optimized memmove optimization for POWER7/powerpc64.
Basically the idea is to use the memcpy for POWER7 on non-overlapped
memory regions and a optimized backward memcpy for memory regions
that overlap (similar to the idea of string/memmove.c).
The backward memcpy algorithm used is similar the one use for memcpy for
POWER7, with adjustments done for alignment. The difference is memory
is always aligned to 16 bytes before using VSX/altivec instructions.
Optimization is achieved on 8 byte aligned strings with double word
comparison using cmpb instruction. On unaligned strings loop unrolling
is applied for Power7 gain.
This patch fixes the optimized ppc64/power7 strncat strlen call for
static build without ifunc enabled. The strlen symbol to call in such
situation is just strlen, instead of __GI_strlen (since the __GI_
alias is just created for shared objects).
The optimization is achieved by following techniques:
> data alignment [gain from aligned memory access on read/write]
> POWER7 gains performance with loop unrolling/unwinding
[gain by reduction of branch penalty].
> zero padding done by calling optimized memset
This patch fixes some powerpc32 and powerpc64 builds with
--disable-multi-arch option along with different --with-cpu=powerN.
It cleanups the Implies directories by removing the multiarch
folder for non multiarch config and also fixing two assembly
implementations: powerpc64/power7/strncat.S that is calling the
wrong strlen; and power8/fpu/s_isnan.S that misses the hidden_def and
weak_alias directives.
This patch add an optimized strpbrk for POWER7 by using a different
algorithm than default implementation: it constructs a table based on
the 'accept' argument and use this table to check for any occurance on
the input string. The idea is similar as x86_64 uses.
For PowerPC some tunings were added, such as unroll loops and memory
clear using VSX instructions.
This patch add a optimized strcspn for POWER7 by using a different
algorithm than default implementation: it constructs a table based on
the 'accept' argument and use this table to check for any occurance
on the input string. The idea is similar as x86_64 uses.
For PowerPC some tunings were added, such as unroll loops and align
stack memory to table to 16 bytes (so VSX clean can ran without
alignment issues).
The optimization is achieved by following techniques:
> hashing of needle.
> hashing avoids scanning of duplicate entries in needle across the string.
> initializing the hash table with Vector instructions (VSX) by quadword access.
> unrolling when scanning for character in string across hash table.
The optimization is achieved by following techniques:
1. Doubleword aligned memory access and compares using
cmpb instruction.
2. Loop unrolling for byte load/store.
3. CPU pre-fetch to avoid cache miss.
This patch optimizes strrchr() for ppc64. It uses aligned memory
access along with cmpb instruction and CPU prefetch to avoid
cache misses for speed improvement.
