On Mon, Jul 27, 2009 at 01:45:06AM +0200, Aurelien Jarno wrote:
> On Sun, Jul 19, 2009 at 04:29:33PM +0200, Aurelien Jarno wrote:
> > On Wed, Jul 15, 2009 at 12:48:02PM -0700, Richard Henderson wrote:
> > > On 07/13/2009 03:16 PM, Matt Turner forwarded:
> > >>>>> The problem is that the memchr() function on alpha uses prefetch, which
> > >>>>> can cause a page boundary to be crossed, while the standards (POSIX and
> > >>>>> C99) says it should stop when a match is found.
> > >
> > > That's not supposed to matter -- faults from prefetch are supposed to be
> > > ignored; see do_page_fault:
> >
> > The problem is that the "prefech" is not done with $31, but using $1 and
> > $3. It is called "prefetch" in the code, but it is more like "read a value
> > in advance".
> >
>
> Knowing that $31 could be used for prefetch, I have modified the
> assembly code from memchr.S to use it. It passes all the testsuite.
>
> Comments are welcome. Then I'll do the alphaev6 version.
Here is the alphaev6 version:
--- a/sysdeps/alpha/alphaev6/memchr.S
+++ b/sysdeps/alpha/alphaev6/memchr.S
@@ -127,7 +127,7 @@ $first_quad:
cmpbge $31, $1, $2 # E :
bne $2, $found_it # U :
# At least one byte left to process.
- ldq $1, 8($0) # L :
+ ldq $31, 8($0) # L :
subq $5, 1, $18 # E : U L U L
addq $0, 8, $0 # E :
@@ -143,38 +143,38 @@ $first_quad:
and $4, 8, $4 # E : odd number of quads?
bne $4, $odd_quad_count # U :
# At least three quads remain to be accessed
- mov $1, $4 # E : L U L U : move prefetched value to correct reg
+ nop # E : L U L U : move prefetched value to correct reg
.align 4
$unrolled_loop:
- ldq $1, 8($0) # L : prefetch $1
- xor $17, $4, $2 # E :
- cmpbge $31, $2, $2 # E :
- bne $2, $found_it # U : U L U L
+ 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 :
- nop # E :
$odd_quad_count:
+ ldq $1, 0($0) # L : load quad
xor $17, $1, $2 # E :
- ldq $4, 8($0) # L : prefetch $4
+ ldq $31, 8($0) # L : prefetch $4
cmpbge $31, $2, $2 # E :
- addq $0, 8, $6 # E :
+ addq $0, 8, $6 # E :
bne $2, $found_it # U :
cmpult $6, $18, $6 # E :
addq $0, 8, $0 # E :
- nop # E :
bne $6, $unrolled_loop # U :
- mov $4, $1 # E : move prefetched value into $1
nop # E :
nop # E :
-
-$final: subq $5, $0, $18 # E : $18 <- number of bytes left to do
nop # E :
+
+$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 :
--
Aurelien Jarno GPG: 1024D/F1BCDB73
aurelien@xxxxxxxxxxx http://www.aurel32.net
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