tilegx: provide optimized strnlen, strstr, and strcasestr

strnlen() is based on the existing tile strlen() with length
checking added.  It speeds up by up to 5x, but on average across
the benchtest corpus by around 35%.  No regressions are seen.

strstr() does 8-byte aligned loads and compares using a 2-byte
filter on the first two bytes of the needle and then testing
the remaining bytes in needle using memcmp().  It speeds up
about 5x in the best case (for "found" needles), about 2x looking
at benchtest as a whole, with some slowdowns as much as 45%.
on a few cases (including the "fail" case for 128KB search).

strcasestr() is based on strstr() but uses a SIMD tolower
routine to convert 8-bytes to lower case in 5 instructions.
It also uses a 2-byte filter and then strncasecmp() for the
remaining bytes.  strncasecmp() is not optimized for SIMD, so
there is futher room for improvement.  However, it is still up
to 16x faster for "found" needles, averaging 2x faster on the
whole corpus of benchtests.  It does slow down by up to 35%
on a few cases, similarly to strstr().

1 files changed, 17 insertions, 5 deletions

diff --git a/sysdeps/tile/tilegx/string-endian.h b/sysdeps/tile/tilegx/string-endian.h
index 47333891e0..2dbc1e4a4f 100644
--- a/sysdeps/tile/tilegx/string-endian.h
+++ b/sysdeps/tile/tilegx/string-endian.h
@@ -16,24 +16,36 @@
    License along with the GNU C Library.  If not, see
    <http://www.gnu.org/licenses/>.  */
 
-/* Provide a mask based on the pointer alignment that
+#include <endian.h>
+#include <stdint.h>
+
+/* Provide a set of macros to help keep endianness #ifdefs out of
+   the string functions.
+
+   MASK: Provide a mask based on the pointer alignment that
    sets up non-zero bytes before the beginning of the string.
    The MASK expression works because shift counts are taken mod 64.
-   Also, specify how to count "first" and "last" bits
-   when the bits have been read as a word.  */
 
-#include <stdint.h>
+   NULMASK: Clear bytes beyond a given point in the string.
+
+   CFZ: Find the first zero bit in the 8 string bytes in a long.
+
+   REVCZ: Find the last zero bit in the 8 string bytes in a long.
+
+   STRSHIFT: Shift N bits towards the start of the string.  */
 
-#ifndef __BIG_ENDIAN__
+#if __BYTE_ORDER == __LITTLE_ENDIAN
 #define MASK(x) (__insn_shl(1ULL, (x << 3)) - 1)
 #define NULMASK(x) ((2ULL << x) - 1)
 #define CFZ(x) __insn_ctz(x)
 #define REVCZ(x) __insn_clz(x)
+#define STRSHIFT(x,n) ((x) >> n)
 #else
 #define MASK(x) (__insn_shl(-2LL, ((-x << 3) - 1)))
 #define NULMASK(x) (-2LL << (63 - x))
 #define CFZ(x) __insn_clz(x)
 #define REVCZ(x) __insn_ctz(x)
+#define STRSHIFT(x,n) ((x) << n)
 #endif
 
 /* Create eight copies of the byte in a uint64_t.  Byte Shuffle uses