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authorChris Metcalf <cmetcalf@tilera.com>2014-09-25 16:49:38 -0400
committerChris Metcalf <cmetcalf@tilera.com>2014-10-06 11:20:59 -0400
commitd9cd52e64d7b6b0fd56566de87c826cb6fe3677d (patch)
tree2e79c9dae8aaf921b08bd73c3af19d65879545cd
parent4b68ea1162f39f62590e49eb5d4371871e071f32 (diff)
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tile: optimize memcmp
Customize memcmp.c for tile, using similar tricks from memcpy: - replace MERGE macro with dblalign. - replace memcmp_bytes function with revbytes. - use __glibc_likely. - use post-increment addressing. The schedule is still not perfect: the compiler is not hoisting code above the comparison branch, which could save a bundle or two. memcmp speeds up by 30-40% on shorter aligned tests in benchtest, with some tests with unaligned lengths taking a small performance hit.
-rw-r--r--ChangeLog2
-rw-r--r--sysdeps/tile/memcmp.c367
2 files changed, 369 insertions, 0 deletions
diff --git a/ChangeLog b/ChangeLog
index 44a45e209a9..7dd6029d2c3 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,7 @@
2014-10-02 Chris Metcalf <cmetcalf@tilera.com>
+ * sysdeps/tile/memcmp.c: New file.
+
* sysdeps/unix/sysv/linux/tile/sysconf.c: New file.
* sysdeps/tile/tilegx/string-endian.h (STRSHIFT): New macro.
diff --git a/sysdeps/tile/memcmp.c b/sysdeps/tile/memcmp.c
new file mode 100644
index 00000000000..8d399217349
--- /dev/null
+++ b/sysdeps/tile/memcmp.c
@@ -0,0 +1,367 @@
+/* Copyright (C) 1991-2014 Free Software Foundation, Inc.
+ This file is part of the GNU C Library.
+ Contributed by Torbjorn Granlund (tege@sics.se).
+
+ 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/>. */
+
+#ifdef HAVE_CONFIG_H
+# include "config.h"
+#endif
+
+#undef __ptr_t
+#define __ptr_t void *
+
+#if defined HAVE_STRING_H || defined _LIBC
+# include <string.h>
+#endif
+
+#undef memcmp
+
+#ifndef MEMCMP
+# define MEMCMP memcmp
+#endif
+
+#ifdef _LIBC
+
+# include <memcopy.h>
+# include <endian.h>
+
+# if __BYTE_ORDER == __BIG_ENDIAN
+# define WORDS_BIGENDIAN
+# endif
+
+#else /* Not in the GNU C library. */
+
+# include <sys/types.h>
+
+/* Type to use for aligned memory operations.
+ This should normally be the biggest type supported by a single load
+ and store. Must be an unsigned type. */
+# define op_t unsigned long int
+# define OPSIZ (sizeof(op_t))
+
+/* Threshold value for when to enter the unrolled loops. */
+# define OP_T_THRES 16
+
+/* Type to use for unaligned operations. */
+typedef unsigned char byte;
+
+#endif /* In the GNU C library. */
+
+/* Provide the appropriate builtins to shift two registers based on
+ the alignment of a pointer held in a third register, and to reverse
+ the bytes in a word. */
+#ifdef __tilegx__
+#define DBLALIGN __insn_dblalign
+#define REVBYTES __insn_revbytes
+#else
+#define DBLALIGN __insn_dword_align
+#define REVBYTES __insn_bytex
+#endif
+
+#ifdef WORDS_BIGENDIAN
+# define CMP_LT_OR_GT(a, b) ((a) > (b) ? 1 : -1)
+#else
+# define CMP_LT_OR_GT(a, b) (REVBYTES(a) > REVBYTES(b) ? 1 : -1)
+#endif
+
+/* BE VERY CAREFUL IF YOU CHANGE THIS CODE! */
+
+/* The strategy of this memcmp is:
+
+ 1. Compare bytes until one of the block pointers is aligned.
+
+ 2. Compare using memcmp_common_alignment or
+ memcmp_not_common_alignment, regarding the alignment of the other
+ block after the initial byte operations. The maximum number of
+ full words (of type op_t) are compared in this way.
+
+ 3. Compare the few remaining bytes. */
+
+static int memcmp_common_alignment (long, long, size_t) __THROW;
+
+/* memcmp_common_alignment -- Compare blocks at SRCP1 and SRCP2 with LEN `op_t'
+ objects (not LEN bytes!). Both SRCP1 and SRCP2 should be aligned for
+ memory operations on `op_t's. */
+static int
+memcmp_common_alignment (srcp1, srcp2, len)
+ long int srcp1;
+ long int srcp2;
+ size_t len;
+{
+ op_t a0, a1;
+ op_t b0, b1;
+
+ switch (len % 4)
+ {
+ default: /* Avoid warning about uninitialized local variables. */
+ case 2:
+ a0 = ((op_t *) srcp1)[0];
+ b0 = ((op_t *) srcp2)[0];
+ srcp1 += OPSIZ;
+ srcp2 += OPSIZ;
+ len += 2;
+ goto do1;
+ case 3:
+ a1 = ((op_t *) srcp1)[0];
+ b1 = ((op_t *) srcp2)[0];
+ srcp1 += OPSIZ;
+ srcp2 += OPSIZ;
+ len += 1;
+ goto do2;
+ case 0:
+ if (OP_T_THRES <= 3 * OPSIZ && len == 0)
+ return 0;
+ a0 = ((op_t *) srcp1)[0];
+ b0 = ((op_t *) srcp2)[0];
+ srcp1 += OPSIZ;
+ srcp2 += OPSIZ;
+ goto do3;
+ case 1:
+ a1 = ((op_t *) srcp1)[0];
+ b1 = ((op_t *) srcp2)[0];
+ srcp1 += OPSIZ;
+ srcp2 += OPSIZ;
+ len -= 1;
+ if (OP_T_THRES <= 3 * OPSIZ && len == 0)
+ goto do0;
+ /* Fall through. */
+ }
+
+ do
+ {
+ a0 = ((op_t *) srcp1)[0];
+ b0 = ((op_t *) srcp2)[0];
+ srcp1 += OPSIZ;
+ srcp2 += OPSIZ;
+ if (__glibc_likely (a1 != b1))
+ return CMP_LT_OR_GT (a1, b1);
+
+ do3:
+ a1 = ((op_t *) srcp1)[0];
+ b1 = ((op_t *) srcp2)[0];
+ srcp1 += OPSIZ;
+ srcp2 += OPSIZ;
+ if (__glibc_likely (a0 != b0))
+ return CMP_LT_OR_GT (a0, b0);
+
+ do2:
+ a0 = ((op_t *) srcp1)[0];
+ b0 = ((op_t *) srcp2)[0];
+ srcp1 += OPSIZ;
+ srcp2 += OPSIZ;
+ if (__glibc_likely (a1 != b1))
+ return CMP_LT_OR_GT (a1, b1);
+
+ do1:
+ a1 = ((op_t *) srcp1)[0];
+ b1 = ((op_t *) srcp2)[0];
+ srcp1 += OPSIZ;
+ srcp2 += OPSIZ;
+ if (__glibc_likely (a0 != b0))
+ return CMP_LT_OR_GT (a0, b0);
+
+ len -= 4;
+ }
+ while (len != 0);
+
+ /* This is the right position for do0. Please don't move
+ it into the loop. */
+ do0:
+ if (__glibc_likely (a1 != b1))
+ return CMP_LT_OR_GT (a1, b1);
+ return 0;
+}
+
+static int memcmp_not_common_alignment (long, long, size_t) __THROW;
+
+/* memcmp_not_common_alignment -- Compare blocks at SRCP1 and SRCP2 with LEN
+ `op_t' objects (not LEN bytes!). SRCP2 should be aligned for memory
+ operations on `op_t', but SRCP1 *should be unaligned*. */
+static int
+memcmp_not_common_alignment (srcp1, srcp2, len)
+ long int srcp1;
+ long int srcp2;
+ size_t len;
+{
+ void * srcp1i;
+ op_t a0, a1, a2, a3;
+ op_t b0, b1, b2, b3;
+ op_t x;
+
+ /* Calculate how to shift a word read at the memory operation
+ aligned srcp1 to make it aligned for comparison. */
+
+ srcp1i = (void *) srcp1;
+
+ /* Make SRCP1 aligned by rounding it down to the beginning of the `op_t'
+ it points in the middle of. */
+ srcp1 &= -OPSIZ;
+
+ switch (len % 4)
+ {
+ default: /* Avoid warning about uninitialized local variables. */
+ case 2:
+ a1 = ((op_t *) srcp1)[0];
+ a2 = ((op_t *) srcp1)[1];
+ b2 = ((op_t *) srcp2)[0];
+ srcp1 += 2 * OPSIZ;
+ srcp2 += 1 * OPSIZ;
+ len += 2;
+ goto do1;
+ case 3:
+ a0 = ((op_t *) srcp1)[0];
+ a1 = ((op_t *) srcp1)[1];
+ b1 = ((op_t *) srcp2)[0];
+ srcp1 += 2 * OPSIZ;
+ srcp2 += 1 * OPSIZ;
+ len += 1;
+ goto do2;
+ case 0:
+ if (OP_T_THRES <= 3 * OPSIZ && len == 0)
+ return 0;
+ a3 = ((op_t *) srcp1)[0];
+ a0 = ((op_t *) srcp1)[1];
+ b0 = ((op_t *) srcp2)[0];
+ srcp1 += 2 * OPSIZ;
+ srcp2 += 1 * OPSIZ;
+ goto do3;
+ case 1:
+ a2 = ((op_t *) srcp1)[0];
+ a3 = ((op_t *) srcp1)[1];
+ b3 = ((op_t *) srcp2)[0];
+ srcp1 += 2 * OPSIZ;
+ srcp2 += 1 * OPSIZ;
+ len -= 1;
+ if (OP_T_THRES <= 3 * OPSIZ && len == 0)
+ goto do0;
+ /* Fall through. */
+ }
+
+ do
+ {
+ a0 = ((op_t *) srcp1)[0];
+ b0 = ((op_t *) srcp2)[0];
+ x = DBLALIGN (a2, a3, srcp1i);
+ srcp1 += OPSIZ;
+ srcp2 += OPSIZ;
+ if (__glibc_likely (x != b3))
+ return CMP_LT_OR_GT (x, b3);
+
+ do3:
+ a1 = ((op_t *) srcp1)[0];
+ b1 = ((op_t *) srcp2)[0];
+ x = DBLALIGN (a3, a0, srcp1i);
+ srcp1 += OPSIZ;
+ srcp2 += OPSIZ;
+ if (__glibc_likely (x != b0))
+ return CMP_LT_OR_GT (x, b0);
+
+ do2:
+ a2 = ((op_t *) srcp1)[0];
+ b2 = ((op_t *) srcp2)[0];
+ x = DBLALIGN (a0, a1, srcp1i);
+ srcp1 += OPSIZ;
+ srcp2 += OPSIZ;
+ if (__glibc_likely (x != b1))
+ return CMP_LT_OR_GT (x, b1);
+
+ do1:
+ a3 = ((op_t *) srcp1)[0];
+ b3 = ((op_t *) srcp2)[0];
+ x = DBLALIGN (a1, a2, srcp1i);
+ srcp1 += OPSIZ;
+ srcp2 += OPSIZ;
+ if (__glibc_likely (x != b2))
+ return CMP_LT_OR_GT (x, b2);
+
+ len -= 4;
+ }
+ while (len != 0);
+
+ /* This is the right position for do0. Please don't move
+ it into the loop. */
+ do0:
+ x = DBLALIGN (a2, a3, srcp1i);
+ if (__glibc_likely (x != b3))
+ return CMP_LT_OR_GT (x, b3);
+ return 0;
+}
+
+int
+MEMCMP (s1, s2, len)
+ const __ptr_t s1;
+ const __ptr_t s2;
+ size_t len;
+{
+ op_t a0;
+ op_t b0;
+ long int srcp1 = (long int) s1;
+ long int srcp2 = (long int) s2;
+ int res;
+
+ if (len >= OP_T_THRES)
+ {
+ /* There are at least some bytes to compare. No need to test
+ for LEN == 0 in this alignment loop. */
+ while (srcp2 % OPSIZ != 0)
+ {
+ a0 = ((byte *) srcp1)[0];
+ b0 = ((byte *) srcp2)[0];
+ srcp1 += 1;
+ srcp2 += 1;
+ res = a0 - b0;
+ if (__glibc_likely (res != 0))
+ return res;
+ len -= 1;
+ }
+
+ /* SRCP2 is now aligned for memory operations on `op_t'.
+ SRCP1 alignment determines if we can do a simple,
+ aligned compare or need to shuffle bits. */
+
+ if (srcp1 % OPSIZ == 0)
+ res = memcmp_common_alignment (srcp1, srcp2, len / OPSIZ);
+ else
+ res = memcmp_not_common_alignment (srcp1, srcp2, len / OPSIZ);
+ if (res != 0)
+ return res;
+
+ /* Number of bytes remaining in the interval [0..OPSIZ-1]. */
+ srcp1 += len & -OPSIZ;
+ srcp2 += len & -OPSIZ;
+ len %= OPSIZ;
+ }
+
+ /* There are just a few bytes to compare. Use byte memory operations. */
+ while (len != 0)
+ {
+ a0 = ((byte *) srcp1)[0];
+ b0 = ((byte *) srcp2)[0];
+ srcp1 += 1;
+ srcp2 += 1;
+ res = a0 - b0;
+ if (__glibc_likely (res != 0))
+ return res;
+ len -= 1;
+ }
+
+ return 0;
+}
+libc_hidden_builtin_def(memcmp)
+#ifdef weak_alias
+# undef bcmp
+weak_alias (memcmp, bcmp)
+#endif