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. diff --git a/sysdeps/alpha/memchr.S b/sysdeps/alpha/memchr.S index 5d713d5..87c7fb1 100644 --- a/sysdeps/alpha/memchr.S +++ b/sysdeps/alpha/memchr.S @@ -119,7 +119,7 @@ $first_quad: # At least one byte left to process. - ldq t0, 8(v0) # e0 : + ldq zero, 8(v0) # e0 : prefetch next quad subq t4, 1, a2 # .. e1 : addq v0, 8, v0 #-e0 : @@ -138,19 +138,19 @@ $first_quad: # At least three quads remain to be accessed - mov t0, t3 # e0 : move prefetched value to correct reg - .align 4 $unrolled_loop: - ldq t0, 8(v0) #-e0 : prefetch t0 - xor a1, t3, t1 # .. e1 : - cmpbge zero, t1, t1 # e0 : - bne t1, $found_it # .. e1 : + 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 #-e0 : + addq v0, 8, v0 # e1 : $odd_quad_count: + ldq t0, 0(v0) # e0 : load quad xor a1, t0, t1 # .. e1 : - ldq t3, 8(v0) # e0 : prefetch t3 + ldq zero, 8(v0) # e0 : prefetch next quad cmpbge zero, t1, t1 # .. e1 : addq v0, 8, t5 #-e0 : bne t1, $found_it # .. e1 : @@ -159,8 +159,8 @@ $odd_quad_count: addq v0, 8, v0 # .. e1 : bne t5, $unrolled_loop #-e1 : - mov t3, t0 # e0 : move prefetched value into t0 -$final: subq t4, v0, a2 # .. e1 : a2 <- number of bytes left to do +$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: -- Aurelien Jarno GPG: 1024D/F1BCDB73 aurelien@xxxxxxxxxxx http://www.aurel32.net -- To unsubscribe from this list: send the line "unsubscribe linux-alpha" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
