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Re: PowerPC LE strnlen
- From: Adhemerval Zanella <azanella at linux dot vnet dot ibm dot com>
- To: libc-alpha at sourceware dot org
- Date: Wed, 21 Aug 2013 15:35:49 -0300
- Subject: Re: PowerPC LE strnlen
- References: <20130809051854 dot GI3294 at bubble dot grove dot modra dot org>
Hi Alan,
Thanks for the patch, it is ok. Using the benchtests with some modification (increase
total iteration for same test and summing results instead of shows only the best one)
I also noticed some performance leverage for PPC32 for size less or equal than 128 bytes.
For PPC64 the perf results seems unaffected.
On 09-08-2013 02:18, Alan Modra wrote:
> The existing strnlen code has a number of defects, so this patch is more
> than just adding little-endian support. The changes here are similar to
> those for memchr.
>
> * sysdeps/powerpc/powerpc64/power7/strnlen.S (strnlen): Add
> little-endian support. Remove unnecessary "are we done" tests.
> Handle "s" wrapping around zero and extremely large "size".
> Correct main loop count. Handle single left-over word from main
> loop inline rather than by using small_loop. Correct comments.
> Delete "zero" tail, use "end_max" instead.
> * sysdeps/powerpc/powerpc32/power7/strnlen.S: Likewise.
>
> diff --git a/sysdeps/powerpc/powerpc64/power7/strnlen.S b/sysdeps/powerpc/powerpc64/power7/strnlen.S
> index 37c7dbf..5159106 100644
> --- a/sysdeps/powerpc/powerpc64/power7/strnlen.S
> +++ b/sysdeps/powerpc/powerpc64/power7/strnlen.S
> @@ -24,33 +24,29 @@
> ENTRY (__strnlen)
> CALL_MCOUNT 2
> dcbt 0,r3
> - clrrdi r8,r3,3
> + clrrdi r8,r3,3
> add r7,r3,r4 /* Calculate the last acceptable address. */
> cmpldi r4,32
> li r0,0 /* Doubleword with null chars. */
> + addi r7,r7,-1
> +
> /* If we have less than 33 bytes to search, skip to a faster code. */
> ble L(small_range)
>
> - cmpld cr7,r3,r7 /* Is the address equal or less than r3? If
> - it's equal or less, it means size is either 0
> - or a negative number. */
> - ble cr7,L(proceed)
> -
> - li r7,-1 /* Make r11 the biggest if r4 <= 0. */
> -L(proceed):
> rlwinm r6,r3,3,26,28 /* Calculate padding. */
> ld r12,0(r8) /* Load doubleword from memory. */
> cmpb r10,r12,r0 /* Check for null bytes in DWORD1. */
> +#ifdef __LITTLE_ENDIAN__
> + srd r10,r10,r6
> + sld r10,r10,r6
> +#else
> sld r10,r10,r6
> srd r10,r10,r6
> +#endif
> cmpldi cr7,r10,0 /* If r10 == 0, no null's have been found. */
> bne cr7,L(done)
>
> - /* Are we done already? */
> - addi r9,r8,8
> - cmpld cr6,r9,r7
> - bge cr6,L(end_max)
> -
> + clrrdi r7,r7,3 /* Address of last doubleword. */
> mtcrf 0x01,r8
> /* Are we now aligned to a quadword boundary? If so, skip to
> the main loop. Otherwise, go through the alignment code. */
> @@ -63,17 +59,18 @@ L(proceed):
> cmpldi cr7,r10,0
> bne cr7,L(done)
>
> - /* Are we done already? */
> - addi r9,r8,8
> - cmpld cr6,r9,r7
> - bge cr6,L(end_max)
> -
> L(loop_setup):
> - sub r5,r7,r9
> + /* The last dword we want to read in the loop below is the one
> + containing the last byte of the string, ie. the dword at
> + (s + size - 1) & ~7, or r7. The first dword read is at
> + r8 + 8, we read 2 * cnt dwords, so the last dword read will
> + be at r8 + 8 + 16 * cnt - 8. Solving for cnt gives
> + cnt = (r7 - r8) / 16 */
> + sub r5,r7,r8
> srdi r6,r5,4 /* Number of loop iterations. */
> mtctr r6 /* Setup the counter. */
> - b L(loop)
> - /* Main loop to look for the null byte backwards in the string. Since
> +
> + /* Main loop to look for the null byte in the string. Since
> it's a small loop (< 8 instructions), align it to 32-bytes. */
> .p2align 5
> L(loop):
> @@ -89,15 +86,18 @@ L(loop):
> cmpldi cr7,r5,0
> bne cr7,L(found)
> bdnz L(loop)
> - /* We're here because the counter reached 0, and that means we
> - didn't have any matches for null in the whole range. Just return
> - the original size. */
> - addi r9,r8,8
> - cmpld cr6,r9,r7
> - blt cr6,L(loop_small)
> +
> + /* We may have one more dword to read. */
> + cmpld cr6,r8,r7
> + beq cr6,L(end_max)
> +
> + ldu r12,8(r8)
> + cmpb r10,r12,r0
> + cmpldi cr6,r10,0
> + bne cr6,L(done)
>
> L(end_max):
> - sub r3,r7,r3
> + mr r3,r4
> blr
>
> /* OK, one (or both) of the doublewords contains a null byte. Check
> @@ -119,52 +119,59 @@ L(found):
> /* r10 has the output of the cmpb instruction, that is, it contains
> 0xff in the same position as the null byte in the original
> doubleword from the string. Use that to calculate the length.
> - We need to make sure the null char is *before* the start of the
> - range (since we're going backwards). */
> + We need to make sure the null char is *before* the end of the
> + range. */
> L(done):
> - cntlzd r0,r10 /* Count leading zeroes before the match. */
> - srdi r0,r0,3 /* Convert leading zeroes to bytes. */
> - add r9,r8,r0
> - sub r6,r9,r3 /* Length until the match. */
> - cmpld r9,r7
> - bgt L(end_max)
> - mr r3,r6
> - blr
> -
> - .align 4
> -L(zero):
> - li r3,0
> +#ifdef __LITTLE_ENDIAN__
> + addi r0,r10,-1
> + andc r0,r0,r10
> + popcntd r0,r0
> +#else
> + cntlzd r0,r10 /* Count leading zeros before the match. */
> +#endif
> + sub r3,r8,r3
> + srdi r0,r0,3 /* Convert leading/trailing zeros to bytes. */
> + add r3,r3,r0 /* Length until the match. */
> + cmpld r3,r4
> + blelr
> + mr r3,r4
> blr
>
> /* Deals with size <= 32. */
> .align 4
> L(small_range):
> cmpldi r4,0
> - beq L(zero)
> + beq L(end_max)
> +
> + clrrdi r7,r7,3 /* Address of last doubleword. */
>
> rlwinm r6,r3,3,26,28 /* Calculate padding. */
> - ld r12,0(r8) /* Load word from memory. */
> + ld r12,0(r8) /* Load doubleword from memory. */
> cmpb r10,r12,r0 /* Check for null bytes in DWORD1. */
> +#ifdef __LITTLE_ENDIAN__
> + srd r10,r10,r6
> + sld r10,r10,r6
> +#else
> sld r10,r10,r6
> srd r10,r10,r6
> +#endif
> cmpldi cr7,r10,0
> bne cr7,L(done)
>
> - addi r9,r8,8
> - cmpld r9,r7
> - bge L(end_max)
> - b L(loop_small)
> + cmpld r8,r7
> + beq L(end_max)
>
> .p2align 5
> L(loop_small):
> ldu r12,8(r8)
> cmpb r10,r12,r0
> - addi r9,r8,8
> cmpldi cr6,r10,0
> bne cr6,L(done)
> - cmpld r9,r7
> - bge L(end_max)
> - b L(loop_small)
> + cmpld r8,r7
> + bne L(loop_small)
> + mr r3,r4
> + blr
> +
> END (__strnlen)
> weak_alias (__strnlen, strnlen)
> libc_hidden_builtin_def (strnlen)
> diff --git a/sysdeps/powerpc/powerpc32/power7/strnlen.S b/sysdeps/powerpc/powerpc32/power7/strnlen.S
> index ed08836..eb52afd 100644
> --- a/sysdeps/powerpc/powerpc32/power7/strnlen.S
> +++ b/sysdeps/powerpc/powerpc32/power7/strnlen.S
> @@ -28,51 +28,47 @@ ENTRY (__strnlen)
> add r7,r3,r4 /* Calculate the last acceptable address. */
> cmplwi r4,16
> li r0,0 /* Word with null chars. */
> + addi r7,r7,-1
> ble L(small_range)
>
> - cmplw cr7,r3,r7 /* Is the address equal or less than r3? If
> - it's equal or less, it means size is either 0
> - or a negative number. */
> - ble cr7,L(proceed)
> -
> - li r7,-1 /* Make r11 the biggest if r4 <= 0. */
> -L(proceed):
> rlwinm r6,r3,3,27,28 /* Calculate padding. */
> lwz r12,0(r8) /* Load word from memory. */
> cmpb r10,r12,r0 /* Check for null bytes in DWORD1. */
> +#ifdef __LITTLE_ENDIAN__
> + srw r10,r10,r6
> + slw r10,r10,r6
> +#else
> slw r10,r10,r6
> srw r10,r10,r6
> +#endif
> cmplwi cr7,r10,0 /* If r10 == 0, no null's have been found. */
> bne cr7,L(done)
>
> - /* Are we done already? */
> - addi r9,r8,4
> - cmplw cr6,r9,r7
> - bge cr6,L(end_max)
> -
> + clrrwi r7,r7,2 /* Address of last word. */
> mtcrf 0x01,r8
> /* Are we now aligned to a doubleword boundary? If so, skip to
> the main loop. Otherwise, go through the alignment code. */
>
> bt 29,L(loop_setup)
>
> - /* Handle DWORD2 of pair. */
> + /* Handle WORD2 of pair. */
> lwzu r12,4(r8)
> cmpb r10,r12,r0
> cmplwi cr7,r10,0
> bne cr7,L(done)
>
> - /* Are we done already? */
> - addi r9,r8,4
> - cmplw cr6,r9,r7
> - bge cr6,L(end_max)
> -
> L(loop_setup):
> - sub r5,r7,r9
> + /* The last word we want to read in the loop below is the one
> + containing the last byte of the string, ie. the word at
> + (s + size - 1) & ~3, or r7. The first word read is at
> + r8 + 4, we read 2 * cnt words, so the last word read will
> + be at r8 + 4 + 8 * cnt - 4. Solving for cnt gives
> + cnt = (r7 - r8) / 8 */
> + sub r5,r7,r8
> srwi r6,r5,3 /* Number of loop iterations. */
> mtctr r6 /* Setup the counter. */
> - b L(loop)
> - /* Main loop to look for the null byte backwards in the string. Since
> +
> + /* Main loop to look for the null byte in the string. Since
> it's a small loop (< 8 instructions), align it to 32-bytes. */
> .p2align 5
> L(loop):
> @@ -88,15 +84,18 @@ L(loop):
> cmplwi cr7,r5,0
> bne cr7,L(found)
> bdnz L(loop)
> - /* We're here because the counter reached 0, and that means we
> - didn't have any matches for null in the whole range. Just return
> - the original size. */
> - addi r9,r8,4
> - cmplw cr6,r9,r7
> - blt cr6,L(loop_small)
> +
> + /* We may have one more word to read. */
> + cmplw cr6,r8,r7
> + beq cr6,L(end_max)
> +
> + lwzu r12,4(r8)
> + cmpb r10,r12,r0
> + cmplwi cr6,r10,0
> + bne cr6,L(done)
>
> L(end_max):
> - sub r3,r7,r3
> + mr r3,r4
> blr
>
> /* OK, one (or both) of the words contains a null byte. Check
> @@ -121,49 +120,56 @@ L(found):
> We need to make sure the null char is *before* the end of the
> range. */
> L(done):
> - cntlzw r0,r10 /* Count leading zeroes before the match. */
> - srwi r0,r0,3 /* Convert leading zeroes to bytes. */
> - add r9,r8,r0
> - sub r6,r9,r3 /* Length until the match. */
> - cmplw r9,r7
> - bgt L(end_max)
> - mr r3,r6
> - blr
> -
> - .align 4
> -L(zero):
> - li r3,0
> +#ifdef __LITTLE_ENDIAN__
> + addi r0,r10,-1
> + andc r0,r0,r10
> + popcntw r0,r0
> +#else
> + cntlzw r0,r10 /* Count leading zeros before the match. */
> +#endif
> + sub r3,r8,r3
> + srwi r0,r0,3 /* Convert leading/trailing zeros to bytes. */
> + add r3,r3,r0 /* Length until the match. */
> + cmplw r3,r4
> + blelr
> + mr r3,r4
> blr
>
> -/* Deals with size <= 32. */
> +/* Deals with size <= 16. */
> .align 4
> L(small_range):
> cmplwi r4,0
> - beq L(zero)
> + beq L(end_max)
> +
> + clrrwi r7,r7,2 /* Address of last word. */
>
> rlwinm r6,r3,3,27,28 /* Calculate padding. */
> lwz r12,0(r8) /* Load word from memory. */
> cmpb r10,r12,r0 /* Check for null bytes in WORD1. */
> +#ifdef __LITTLE_ENDIAN__
> + srw r10,r10,r6
> + slw r10,r10,r6
> +#else
> slw r10,r10,r6
> srw r10,r10,r6
> +#endif
> cmplwi cr7,r10,0
> bne cr7,L(done)
>
> - addi r9,r8,4
> - cmplw r9,r7
> - bge L(end_max)
> - b L(loop_small)
> + cmplw r8,r7
> + beq L(end_max)
>
> .p2align 5
> L(loop_small):
> lwzu r12,4(r8)
> cmpb r10,r12,r0
> - addi r9,r8,4
> cmplwi cr6,r10,0
> bne cr6,L(done)
> - cmplw r9,r7
> - bge L(end_max)
> - b L(loop_small)
> + cmplw r8,r7
> + bne L(loop_small)
> + mr r3,r4
> + blr
> +
> END (__strnlen)
> weak_alias (__strnlen, strnlen)
> libc_hidden_builtin_def (strnlen)
>