* [2.27 COMMITTED][AArch64] Backport strncmp improvements
@ 2019-01-01 0:00 Wilco Dijkstra
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From: Wilco Dijkstra @ 2019-01-01 0:00 UTC (permalink / raw)
To: libc-stable; +Cc: nd
commit 0fc5934ebd13ee4e1c12224d0e9206b76d10c626
Author: Siddhesh Poyarekar <siddhesh@sourceware.org>
Date: Thu Mar 15 08:06:21 2018 +0530
aarch64/strncmp: Use lsr instead of mov+lsr
A lsr can do what the mov and lsr did.
(cherry picked from commit b47c3e7637efb77818cbef55dcd0ed1f0ea0ddf1)
commit e0a0bd3accf5837d8fa6b6907923c13b9ac0e0ff
Author: Siddhesh Poyarekar <siddhesh@sourceware.org>
Date: Wed Mar 14 18:51:05 2018 +0530
aarch64/strncmp: Unbreak builds with old binutils
Binutils 2.26.* and older do not support moves with shifted registers,
so use a separate shift instruction instead.
(cherry picked from commit d46f84de745db8f3f06a37048261f4e5ceacf0a3)
commit 638caf300022aab68f4c464f57e8b8ac879f5735
Author: Siddhesh Poyarekar <siddhesh@sourceware.org>
Date: Tue Mar 13 23:57:03 2018 +0530
aarch64: Improve strncmp for mutually misaligned inputs
The mutually misaligned inputs on aarch64 are compared with a simple
byte copy, which is not very efficient. Enhance the comparison
similar to strcmp by loading a double-word at a time. The peak
performance improvement (i.e. 4k maxlen comparisons) due to this on
the strncmp microbenchmark is as follows:
falkor: 3.5x (up to 72% time reduction)
cortex-a73: 3.5x (up to 71% time reduction)
cortex-a53: 3.5x (up to 71% time reduction)
All mutually misaligned inputs from 16 bytes maxlen onwards show
upwards of 15% improvement and there is no measurable effect on the
performance of aligned/mutually aligned inputs.
* sysdeps/aarch64/strncmp.S (count): New macro.
(strncmp): Store misaligned length in SRC1 in COUNT.
(mutual_align): Adjust.
(misaligned8): Load dword at a time when it is safe.
(cherry picked from commit 7108f1f944792ac68332967015d5e6418c5ccc88)
diff --git a/ChangeLog b/ChangeLog
index 5ddc3e7..99b6180 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,22 @@
2019-09-06 Siddhesh Poyarekar <siddhesh@sourceware.org>
+ * sysdeps/aarch64/strncmp.S (strncmp): Use lsr instead of
+ mov + lsr.
+
+2019-09-06 Siddhesh Poyarekar <siddhesh@sourceware.org>
+
+ * sysdeps/aarch64/strncmp.S (strncmp): Use a separate shift
+ instruction to unbreak builds with binutils 2.26 and older.
+
+2019-09-06 Siddhesh Poyarekar <siddhesh@sourceware.org>
+
+ * sysdeps/aarch64/strncmp.S (count): New macro.
+ (strncmp): Store misaligned length in SRC1 in COUNT.
+ (mutual_align): Adjust.
+ (misaligned8): Load dword at a time when it is safe.
+
+2019-09-06 Siddhesh Poyarekar <siddhesh@sourceware.org>
+
* sysdeps/aarch64/strcmp.S (do_misaligned): Jump back to
do_misaligned, not misaligned8.
diff --git a/sysdeps/aarch64/strncmp.S b/sysdeps/aarch64/strncmp.S
index a08d2c0..759c752 100644
--- a/sysdeps/aarch64/strncmp.S
+++ b/sysdeps/aarch64/strncmp.S
@@ -49,6 +49,7 @@
#define limit_wd x13
#define mask x14
#define endloop x15
+#define count mask
ENTRY_ALIGN_AND_PAD (strncmp, 6, 7)
DELOUSE (0)
@@ -58,9 +59,9 @@ ENTRY_ALIGN_AND_PAD (strncmp, 6, 7)
eor tmp1, src1, src2
mov zeroones, #REP8_01
tst tmp1, #7
+ and count, src1, #7
b.ne L(misaligned8)
- ands tmp1, src1, #7
- b.ne L(mutual_align)
+ cbnz count, L(mutual_align)
/* Calculate the number of full and partial words -1. */
sub limit_wd, limit, #1 /* limit != 0, so no underflow. */
lsr limit_wd, limit_wd, #3 /* Convert to Dwords. */
@@ -165,43 +166,107 @@ L(mutual_align):
bic src1, src1, #7
bic src2, src2, #7
ldr data1, [src1], #8
- neg tmp3, tmp1, lsl #3 /* 64 - bits(bytes beyond align). */
+ neg tmp3, count, lsl #3 /* 64 - bits(bytes beyond align). */
ldr data2, [src2], #8
mov tmp2, #~0
sub limit_wd, limit, #1 /* limit != 0, so no underflow. */
#ifdef __AARCH64EB__
/* Big-endian. Early bytes are at MSB. */
- lsl tmp2, tmp2, tmp3 /* Shift (tmp1 & 63). */
+ lsl tmp2, tmp2, tmp3 /* Shift (count & 63). */
#else
/* Little-endian. Early bytes are at LSB. */
- lsr tmp2, tmp2, tmp3 /* Shift (tmp1 & 63). */
+ lsr tmp2, tmp2, tmp3 /* Shift (count & 63). */
#endif
and tmp3, limit_wd, #7
lsr limit_wd, limit_wd, #3
/* Adjust the limit. Only low 3 bits used, so overflow irrelevant. */
- add limit, limit, tmp1
- add tmp3, tmp3, tmp1
+ add limit, limit, count
+ add tmp3, tmp3, count
orr data1, data1, tmp2
orr data2, data2, tmp2
add limit_wd, limit_wd, tmp3, lsr #3
b L(start_realigned)
-L(ret0):
- mov result, #0
- RET
-
.p2align 6
+ /* Don't bother with dwords for up to 16 bytes. */
L(misaligned8):
- sub limit, limit, #1
-1:
+ cmp limit, #16
+ b.hs L(try_misaligned_words)
+
+L(byte_loop):
/* Perhaps we can do better than this. */
ldrb data1w, [src1], #1
ldrb data2w, [src2], #1
subs limit, limit, #1
- ccmp data1w, #1, #0, cs /* NZCV = 0b0000. */
+ ccmp data1w, #1, #0, hi /* NZCV = 0b0000. */
ccmp data1w, data2w, #0, cs /* NZCV = 0b0000. */
- b.eq 1b
+ b.eq L(byte_loop)
+L(done):
sub result, data1, data2
RET
+
+ /* Align the SRC1 to a dword by doing a bytewise compare and then do
+ the dword loop. */
+L(try_misaligned_words):
+ lsr limit_wd, limit, #3
+ cbz count, L(do_misaligned)
+
+ neg count, count
+ and count, count, #7
+ sub limit, limit, count
+ lsr limit_wd, limit, #3
+
+L(page_end_loop):
+ ldrb data1w, [src1], #1
+ ldrb data2w, [src2], #1
+ cmp data1w, #1
+ ccmp data1w, data2w, #0, cs /* NZCV = 0b0000. */
+ b.ne L(done)
+ subs count, count, #1
+ b.hi L(page_end_loop)
+
+L(do_misaligned):
+ /* Prepare ourselves for the next page crossing. Unlike the aligned
+ loop, we fetch 1 less dword because we risk crossing bounds on
+ SRC2. */
+ mov count, #8
+ subs limit_wd, limit_wd, #1
+ b.lo L(done_loop)
+L(loop_misaligned):
+ and tmp2, src2, #0xff8
+ eor tmp2, tmp2, #0xff8
+ cbz tmp2, L(page_end_loop)
+
+ ldr data1, [src1], #8
+ ldr data2, [src2], #8
+ sub tmp1, data1, zeroones
+ orr tmp2, data1, #REP8_7f
+ eor diff, data1, data2 /* Non-zero if differences found. */
+ bics has_nul, tmp1, tmp2 /* Non-zero if NUL terminator. */
+ ccmp diff, #0, #0, eq
+ b.ne L(not_limit)
+ subs limit_wd, limit_wd, #1
+ b.pl L(loop_misaligned)
+
+L(done_loop):
+ /* We found a difference or a NULL before the limit was reached. */
+ and limit, limit, #7
+ cbz limit, L(not_limit)
+ /* Read the last word. */
+ sub src1, src1, 8
+ sub src2, src2, 8
+ ldr data1, [src1, limit]
+ ldr data2, [src2, limit]
+ sub tmp1, data1, zeroones
+ orr tmp2, data1, #REP8_7f
+ eor diff, data1, data2 /* Non-zero if differences found. */
+ bics has_nul, tmp1, tmp2 /* Non-zero if NUL terminator. */
+ ccmp diff, #0, #0, eq
+ b.ne L(not_limit)
+
+L(ret0):
+ mov result, #0
+ RET
+
END (strncmp)
libc_hidden_builtin_def (strncmp)
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2019-01-01 0:00 [2.27 COMMITTED][AArch64] Backport strncmp improvements Wilco Dijkstra
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