alpha: rewrite memchr.

[BZ #12019]
The new implementation does not read too much data.
This commit is contained in:
Richard Henderson 2010-09-15 10:41:43 -07:00
parent 7ffd2bd725
commit 926cf114f7
4 changed files with 183 additions and 370 deletions

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2010-05-05 Richard Henderson <rth@redhat.com>
2010-09-23 Richard Henderson <rth@redhat.com>
[BZ #12019]
* sysdeps/alpha/alphaev6/memchr.S: Remove.
* sysdeps/alpha/memchr.S: Remove.
* sysdeps/alpha/memchr.c: New.
2010-09-23 Richard Henderson <rth@redhat.com>
[BZ #1864]
* sysdeps/unix/sysv/linux/alpha/fstatfs64.c: New.

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/* Copyright (C) 2000, 2003 Free Software Foundation, Inc.
This file is part of the GNU C Library.
Contributed by David Mosberger (davidm@cs.arizona.edu).
EV6 optimized by Rick Gorton <rick.gorton@alpha-processor.com>.
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, write to the Free
Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
02111-1307 USA. */
#include <sysdep.h>
.arch ev6
.set noreorder
.set noat
ENTRY(__memchr)
#ifdef PROF
ldgp gp, 0(pv)
lda AT, _mcount
jsr AT, (AT), _mcount
.prologue 1
#else
.prologue 0
#endif
# Hack -- if someone passes in (size_t)-1, hoping to just
# search til the end of the address space, we will overflow
# below when we find the address of the last byte. Given
# that we will never have a 56-bit address space, cropping
# the length is the easiest way to avoid trouble.
zap $18, 0x80, $5 # U : Bound length
beq $18, $not_found # U :
ldq_u $1, 0($16) # L : load first quadword Latency=3
and $17, 0xff, $17 # E : L L U U : 00000000000000ch
insbl $17, 1, $2 # U : 000000000000ch00
cmpult $18, 9, $4 # E : small (< 1 quad) string?
or $2, $17, $17 # E : 000000000000chch
lda $3, -1($31) # E : U L L U
sll $17, 16, $2 # U : 00000000chch0000
addq $16, $5, $5 # E : Max search address
or $2, $17, $17 # E : 00000000chchchch
sll $17, 32, $2 # U : U L L U : chchchch00000000
or $2, $17, $17 # E : chchchchchchchch
extql $1, $16, $7 # U : $7 is upper bits
beq $4, $first_quad # U :
ldq_u $6, -1($5) # L : L U U L : eight or less bytes to search Latency=3
extqh $6, $16, $6 # U : 2 cycle stall for $6
mov $16, $0 # E :
nop # E :
or $7, $6, $1 # E : L U L U $1 = quadword starting at $16
# Deal with the case where at most 8 bytes remain to be searched
# in $1. E.g.:
# $18 = 6
# $1 = ????c6c5c4c3c2c1
$last_quad:
negq $18, $6 # E :
xor $17, $1, $1 # E :
srl $3, $6, $6 # U : $6 = mask of $18 bits set
cmpbge $31, $1, $2 # E : L U L U
nop
nop
and $2, $6, $2 # E :
beq $2, $not_found # U : U L U L
$found_it:
#if defined(__alpha_fix__) && defined(__alpha_cix__)
/*
* Since we are guaranteed to have set one of the bits, we don't
* have to worry about coming back with a 0x40 out of cttz...
*/
cttz $2, $3 # U0 :
addq $0, $3, $0 # E : All done
nop # E :
ret # L0 : L U L U
#else
/*
* Slow and clunky. It can probably be improved.
* An exercise left for others.
*/
negq $2, $3 # E :
and $2, $3, $2 # E :
and $2, 0x0f, $1 # E :
addq $0, 4, $3 # E :
cmoveq $1, $3, $0 # E : Latency 2, extra map cycle
nop # E : keep with cmov
and $2, 0x33, $1 # E :
addq $0, 2, $3 # E : U L U L : 2 cycle stall on $0
cmoveq $1, $3, $0 # E : Latency 2, extra map cycle
nop # E : keep with cmov
and $2, 0x55, $1 # E :
addq $0, 1, $3 # E : U L U L : 2 cycle stall on $0
cmoveq $1, $3, $0 # E : Latency 2, extra map cycle
nop
nop
ret # L0 : L U L U
#endif
# Deal with the case where $18 > 8 bytes remain to be
# searched. $16 may not be aligned.
.align 4
$first_quad:
andnot $16, 0x7, $0 # E :
insqh $3, $16, $2 # U : $2 = 0000ffffffffffff ($16<0:2> ff)
xor $1, $17, $1 # E :
or $1, $2, $1 # E : U L U L $1 = ====ffffffffffff
cmpbge $31, $1, $2 # E :
bne $2, $found_it # U :
# At least one byte left to process.
ldq $31, 8($0) # L :
subq $5, 1, $18 # E : U L U L
addq $0, 8, $0 # E :
# Make $18 point to last quad to be accessed (the
# last quad may or may not be partial).
andnot $18, 0x7, $18 # E :
cmpult $0, $18, $2 # E :
beq $2, $final # U : U L U L
# At least two quads remain to be accessed.
subq $18, $0, $4 # E : $4 <- nr quads to be processed
and $4, 8, $4 # E : odd number of quads?
bne $4, $odd_quad_count # U :
# At least three quads remain to be accessed
nop # E : L U L U : move prefetched value to correct reg
.align 4
$unrolled_loop:
ldq $1, 0($0) # L : load quad
xor $17, $1, $2 # E :
ldq $31, 8($0) # L : prefetch next quad
cmpbge $31, $2, $2 # E : U L U L
bne $2, $found_it # U :
addq $0, 8, $0 # E :
nop # E :
nop # E :
$odd_quad_count:
ldq $1, 0($0) # L : load quad
xor $17, $1, $2 # E :
ldq $31, 8($0) # L : prefetch $4
cmpbge $31, $2, $2 # E :
addq $0, 8, $6 # E :
bne $2, $found_it # U :
cmpult $6, $18, $6 # E :
addq $0, 8, $0 # E :
bne $6, $unrolled_loop # U :
nop # E :
nop # E :
nop # E :
$final: ldq $1, 0($0) # L : load last quad
subq $5, $0, $18 # E : $18 <- number of bytes left to do
nop # E :
bne $18, $last_quad # U :
$not_found:
mov $31, $0 # E :
nop # E :
nop # E :
ret # L0 :
END(__memchr)
weak_alias (__memchr, memchr)
#if !__BOUNDED_POINTERS__
weak_alias (__memchr, __ubp_memchr)
#endif
libc_hidden_builtin_def (memchr)

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/* Copyright (C) 1996, 2000, 2003 Free Software Foundation, Inc.
This file is part of the GNU C Library.
Contributed by David Mosberger (davidm@cs.arizona.edu).
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, write to the Free
Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
02111-1307 USA. */
/* Finds characters in a memory area. Optimized for the Alpha:
- memory accessed as aligned quadwords only
- uses cmpbge to compare 8 bytes in parallel
- does binary search to find 0 byte in last
quadword (HAKMEM needed 12 instructions to
do this instead of the 9 instructions that
binary search needs).
For correctness consider that:
- only minimum number of quadwords may be accessed
- the third argument is an unsigned long
*/
#include <sysdep.h>
.set noreorder
.set noat
ENTRY(__memchr)
#ifdef PROF
ldgp gp, 0(pv)
lda AT, _mcount
jsr AT, (AT), _mcount
.prologue 1
#else
.prologue 0
#endif
# Hack -- if someone passes in (size_t)-1, hoping to just
# search til the end of the address space, we will overflow
# below when we find the address of the last byte. Given
# that we will never have a 56-bit address space, cropping
# the length is the easiest way to avoid trouble.
zap a2, 0x80, t4 #-e0 :
beq a2, $not_found # .. e1 :
ldq_u t0, 0(a0) # e1 : load first quadword
insbl a1, 1, t1 # .. e0 : t1 = 000000000000ch00
and a1, 0xff, a1 #-e0 : a1 = 00000000000000ch
cmpult a2, 9, t3 # .. e1 :
or t1, a1, a1 # e0 : a1 = 000000000000chch
lda t2, -1(zero) # .. e1 :
sll a1, 16, t1 #-e0 : t1 = 00000000chch0000
addq a0, t4, t4 # .. e1 :
or t1, a1, a1 # e1 : a1 = 00000000chchchch
unop # :
sll a1, 32, t1 #-e0 : t1 = chchchch00000000
or t1, a1, a1 # e1 : a1 = chchchchchchchch
extql t0, a0, t6 # e0 :
beq t3, $first_quad # .. e1 :
ldq_u t5, -1(t4) #-e1 : eight or less bytes to search
extqh t5, a0, t5 # .. e0 :
mov a0, v0 # e0 :
or t6, t5, t0 # .. e1 : t0 = quadword starting at a0
# Deal with the case where at most 8 bytes remain to be searched
# in t0. E.g.:
# a2 = 6
# t0 = ????c6c5c4c3c2c1
$last_quad:
negq a2, t5 #-e0 :
xor a1, t0, t0 # .. e1 :
srl t2, t5, t5 # e0 : t5 = mask of a2 bits set
cmpbge zero, t0, t1 # .. e1 :
and t1, t5, t1 #-e0 :
beq t1, $not_found # .. e1 :
$found_it:
# Now, determine which byte matched:
negq t1, t2 # e0 :
and t1, t2, t1 # e1 :
and t1, 0x0f, t0 #-e0 :
addq v0, 4, t2 # .. e1 :
cmoveq t0, t2, v0 # e0 :
addq v0, 2, t2 # .. e1 :
and t1, 0x33, t0 #-e0 :
cmoveq t0, t2, v0 # .. e1 :
and t1, 0x55, t0 # e0 :
addq v0, 1, t2 # .. e1 :
cmoveq t0, t2, v0 #-e0 :
$done: ret # .. e1 :
# Deal with the case where a2 > 8 bytes remain to be
# searched. a0 may not be aligned.
.align 4
$first_quad:
andnot a0, 0x7, v0 #-e1 :
insqh t2, a0, t1 # .. e0 : t1 = 0000ffffffffffff (a0<0:2> ff)
xor t0, a1, t0 # e0 :
or t0, t1, t0 # e1 : t0 = ====ffffffffffff
cmpbge zero, t0, t1 #-e0 :
bne t1, $found_it # .. e1 :
# At least one byte left to process.
ldq zero, 8(v0) # e0 : prefetch next quad
subq t4, 1, a2 # .. e1 :
addq v0, 8, v0 #-e0 :
# Make a2 point to last quad to be accessed (the
# last quad may or may not be partial).
andnot a2, 0x7, a2 # .. e1 :
cmpult v0, a2, t1 # e0 :
beq t1, $final # .. e1 :
# At least two quads remain to be accessed.
subq a2, v0, t3 #-e0 : t3 <- nr quads to be processed
and t3, 8, t3 # e1 : odd number of quads?
bne t3, $odd_quad_count # e1 :
# At least three quads remain to be accessed
.align 4
$unrolled_loop:
ldq t0, 0(v0) # e0 : load quad
xor a1, t0, t1 # .. e1 :
ldq zero, 8(v0) # e0 : prefetch next quad
cmpbge zero, t1, t1 # .. e1:
bne t1, $found_it # e0 :
addq v0, 8, v0 # e1 :
$odd_quad_count:
ldq t0, 0(v0) # e0 : load quad
xor a1, t0, t1 # .. e1 :
ldq zero, 8(v0) # e0 : prefetch next quad
cmpbge zero, t1, t1 # .. e1 :
addq v0, 8, t5 #-e0 :
bne t1, $found_it # .. e1 :
cmpult t5, a2, t5 # e0 :
addq v0, 8, v0 # .. e1 :
bne t5, $unrolled_loop #-e1 :
$final: ldq t0, 0(v0) # e0 : load last quad
subq t4, v0, a2 # .. e1 : a2 <- number of bytes left to do
bne a2, $last_quad # e1 :
$not_found:
mov zero, v0 #-e0 :
ret # .. e1 :
END(__memchr)
weak_alias (__memchr, memchr)
#if !__BOUNDED_POINTERS__
weak_alias (__memchr, __ubp_memchr)
#endif
libc_hidden_builtin_def (memchr)

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sysdeps/alpha/memchr.c Normal file
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/* Copyright (C) 2010 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, write to the Free
Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
02111-1307 USA. */
#include <string.h>
typedef unsigned long word;
static inline word
ldq_u(const void *s)
{
return *(const word *)((word)s & -8);
}
#define unlikely(X) __builtin_expect ((X), 0)
#define prefetch(X) __builtin_prefetch ((void *)(X), 0)
#define cmpbeq0(X) __builtin_alpha_cmpbge(0, (X))
#define find(X, Y) cmpbeq0 ((X) ^ (Y))
/* Search no more than N bytes of S for C. */
void *
__memchr (const void *s, int xc, size_t n)
{
const word *s_align;
word t, current, found, mask, offset;
if (unlikely (n == 0))
return 0;
current = ldq_u (s);
/* Replicate low byte of XC into all bytes of C. */
t = xc & 0xff; /* 0000000c */
t = (t << 8) | t; /* 000000cc */
t = (t << 16) | t; /* 0000cccc */
const word c = (t << 32) | t; /* cccccccc */
/* Align the source, and decrement the count by the number
of bytes searched in the first word. */
s_align = (const word *)(s & -8);
n += (s & 7);
/* Deal with misalignment in the first word for the comparison. */
mask = (1ul << (s & 7)) - 1;
/* If the entire string fits within one word, we may need masking
at both the front and the back of the string. */
if (unlikely (n <= 8))
{
mask |= -1ul << n;
goto last_quad;
}
found = find (current, c) & ~mask;
if (unlikely (found))
goto found_it;
s_align++;
n -= 8;
/* If the block is sufficiently large, align to cacheline and prefetch. */
if (unlikely (n >= 256))
{
/* Prefetch 3 cache lines beyond the one we're working on. */
prefetch (s_align + 8);
prefetch (s_align + 16);
prefetch (s_align + 24);
while ((word)s_align & 63)
{
current = *s_align;
found = find (current, c);
if (found)
goto found_it;
s_align++;
n -= 8;
}
/* Within each cacheline, advance the load for the next word
before the test for the previous word is complete. This
allows us to hide the 3 cycle L1 cache load latency. We
only perform this advance load within a cacheline to prevent
reading across page boundary. */
#define CACHELINE_LOOP \
do { \
word i, next = s_align[0]; \
for (i = 0; i < 7; ++i) \
{ \
current = next; \
next = s_align[1]; \
found = find (current, c); \
if (unlikely (found)) \
goto found_it; \
s_align++; \
} \
current = next; \
found = find (current, c); \
if (unlikely (found)) \
goto found_it; \
s_align++; \
n -= 64; \
} while (0)
/* While there's still lots more data to potentially be read,
continue issuing prefetches for the 4th cacheline out. */
while (n >= 256)
{
prefetch (s_align + 24);
CACHELINE_LOOP;
}
/* Up to 3 cache lines remaining. Continue issuing advanced
loads, but stop prefetching. */
while (n >= 64)
CACHELINE_LOOP;
/* We may have exhausted the buffer. */
if (n == 0)
return NULL;
}
/* Quadword aligned loop. */
current = *s_align;
while (n > 8)
{
found = find (current, c);
if (unlikely (found))
goto found_it;
current = *++s_align;
n -= 8;
}
/* The last word may need masking at the tail of the compare. */
mask = -1ul << n;
last_quad:
found = find (current, c) & ~mask;
if (found == 0)
return NULL;
found_it:
#ifdef __alpha_cix__
offset = __builtin_alpha_cttz (found);
#else
/* Extract LSB. */
found &= -found;
/* Binary search for the LSB. */
offset = (found & 0x0f ? 0 : 4);
offset += (found & 0x33 ? 0 : 2);
offset += (found & 0x55 ? 0 : 1);
#endif
return (void *)((word)s_align + offset);
}
#ifdef weak_alias
weak_alias (__memchr, BP_SYM (memchr))
#endif
libc_hidden_builtin_def (memchr)