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PowerPC LE strlen
http://sourceware.org/ml/libc-alpha/2013-08/msg00097.html This is the first of nine patches adding little-endian support to the existing optimised string and memory functions. I did spend some time with a power7 simulator looking at cycle by cycle behaviour for memchr, but most of these patches have not been run on cpu simulators to check that we are going as fast as possible. I'm sure PowerPC can do better. However, the little-endian support mostly leaves main loops unchanged, so I'm banking on previous authors having done a good job on big-endian.. As with most code you stare at long enough, I found some improvements for big-endian too. Little-endian support for strlen. Like most of the string functions, I leave the main word or multiple-word loops substantially unchanged, just needing to modify the tail. Removing the branch in the power7 functions is just a tidy. .align produces a branch anyway. Modifying regs in the non-power7 functions is to suit the new little-endian tail. * sysdeps/powerpc/powerpc64/power7/strlen.S (strlen): Add little-endian support. Don't branch over align. * sysdeps/powerpc/powerpc32/power7/strlen.S: Likewise. * sysdeps/powerpc/powerpc64/strlen.S (strlen): Add little-endian support. Rearrange tmp reg use to suit. Comment. * sysdeps/powerpc/powerpc32/strlen.S: Likewise.
This commit is contained in:
Alan Modra
parent
f7c399cff5
commit
db9b4570c5
@ -1,3 +1,12 @@
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2013-10-04 Alan Modra <amodra@gmail.com>
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* sysdeps/powerpc/powerpc64/power7/strlen.S (strlen): Add little-endian
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support. Don't branch over align.
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* sysdeps/powerpc/powerpc32/power7/strlen.S: Likewise.
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* sysdeps/powerpc/powerpc64/strlen.S (strlen): Add little-endian
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support. Rearrange tmp reg use to suit. Comment.
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* sysdeps/powerpc/powerpc32/strlen.S: Likewise.
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2013-10-04 Alan Modra <amodra@gmail.com>
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* sysdeps/unix/sysv/linux/powerpc/bits/sigstack.h: New file.
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@ -29,7 +29,11 @@ ENTRY (strlen)
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li r0,0 /* Word with null chars to use with cmpb. */
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li r5,-1 /* MASK = 0xffffffffffffffff. */
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lwz r12,0(r4) /* Load word from memory. */
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#ifdef __LITTLE_ENDIAN__
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slw r5,r5,r6
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#else
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srw r5,r5,r6 /* MASK = MASK >> padding. */
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#endif
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orc r9,r12,r5 /* Mask bits that are not part of the string. */
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cmpb r10,r9,r0 /* Check for null bytes in WORD1. */
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cmpwi cr7,r10,0 /* If r10 == 0, no null's have been found. */
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@ -47,9 +51,6 @@ ENTRY (strlen)
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cmpb r10,r12,r0
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cmpwi cr7,r10,0
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bne cr7,L(done)
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b L(loop) /* We branch here (rather than falling through)
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to skip the nops due to heavy alignment
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of the loop below. */
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/* Main loop to look for the end of the string. Since it's a
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small loop (< 8 instructions), align it to 32-bytes. */
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@ -86,9 +87,15 @@ L(loop):
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0xff in the same position as the null byte in the original
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word from the string. Use that to calculate the length. */
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L(done):
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cntlzw r0,r10 /* Count leading zeroes before the match. */
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#ifdef __LITTLE_ENDIAN__
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addi r9, r10, -1 /* Form a mask from trailing zeros. */
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andc r9, r9, r10
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popcntw r0, r9 /* Count the bits in the mask. */
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#else
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cntlzw r0,r10 /* Count leading zeros before the match. */
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#endif
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subf r5,r3,r4
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srwi r0,r0,3 /* Convert leading zeroes to bytes. */
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srwi r0,r0,3 /* Convert leading zeros to bytes. */
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add r3,r5,r0 /* Compute final length. */
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blr
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END (strlen)
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@ -29,7 +29,12 @@
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1 is subtracted you get a value in the range 0x00-0x7f, none of which
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have their high bit set. The expression here is
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(x + 0xfefefeff) & ~(x | 0x7f7f7f7f), which gives 0x00000000 when
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there were no 0x00 bytes in the word.
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there were no 0x00 bytes in the word. You get 0x80 in bytes that
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match, but possibly false 0x80 matches in the next more significant
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byte to a true match due to carries. For little-endian this is
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of no consequence since the least significant match is the one
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we're interested in, but big-endian needs method 2 to find which
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byte matches.
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2) Given a word 'x', we can test to see _which_ byte was zero by
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calculating ~(((x & 0x7f7f7f7f) + 0x7f7f7f7f) | x | 0x7f7f7f7f).
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@ -72,7 +77,7 @@
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ENTRY (strlen)
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#define rTMP1 r0
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#define rTMP4 r0
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#define rRTN r3 /* incoming STR arg, outgoing result */
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#define rSTR r4 /* current string position */
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#define rPADN r5 /* number of padding bits we prepend to the
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@ -82,9 +87,9 @@ ENTRY (strlen)
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#define rWORD1 r8 /* current string word */
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#define rWORD2 r9 /* next string word */
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#define rMASK r9 /* mask for first string word */
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#define rTMP2 r10
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#define rTMP3 r11
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#define rTMP4 r12
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#define rTMP1 r10
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#define rTMP2 r11
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#define rTMP3 r12
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clrrwi rSTR, rRTN, 2
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@ -93,15 +98,20 @@ ENTRY (strlen)
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lwz rWORD1, 0(rSTR)
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li rMASK, -1
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addi r7F7F, r7F7F, 0x7f7f
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/* That's the setup done, now do the first pair of words.
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We make an exception and use method (2) on the first two words, to reduce
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overhead. */
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/* We use method (2) on the first two words, because rFEFE isn't
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required which reduces setup overhead. Also gives a faster return
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for small strings on big-endian due to needing to recalculate with
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method (2) anyway. */
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#ifdef __LITTLE_ENDIAN__
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slw rMASK, rMASK, rPADN
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#else
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srw rMASK, rMASK, rPADN
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#endif
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and rTMP1, r7F7F, rWORD1
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or rTMP2, r7F7F, rWORD1
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add rTMP1, rTMP1, r7F7F
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nor rTMP1, rTMP2, rTMP1
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and. rWORD1, rTMP1, rMASK
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nor rTMP3, rTMP2, rTMP1
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and. rTMP3, rTMP3, rMASK
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mtcrf 0x01, rRTN
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bne L(done0)
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lis rFEFE, -0x101
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@ -110,11 +120,12 @@ ENTRY (strlen)
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bt 29, L(loop)
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/* Handle second word of pair. */
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/* Perhaps use method (1) here for little-endian, saving one instruction? */
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lwzu rWORD1, 4(rSTR)
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and rTMP1, r7F7F, rWORD1
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or rTMP2, r7F7F, rWORD1
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add rTMP1, rTMP1, r7F7F
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nor. rWORD1, rTMP2, rTMP1
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nor. rTMP3, rTMP2, rTMP1
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bne L(done0)
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/* The loop. */
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@ -128,28 +139,52 @@ L(loop):
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add rTMP3, rFEFE, rWORD2
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nor rTMP4, r7F7F, rWORD2
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bne L(done1)
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and. rTMP1, rTMP3, rTMP4
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and. rTMP3, rTMP3, rTMP4
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beq L(loop)
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#ifndef __LITTLE_ENDIAN__
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and rTMP1, r7F7F, rWORD2
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add rTMP1, rTMP1, r7F7F
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andc rWORD1, rTMP4, rTMP1
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andc rTMP3, rTMP4, rTMP1
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b L(done0)
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L(done1):
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and rTMP1, r7F7F, rWORD1
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subi rSTR, rSTR, 4
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add rTMP1, rTMP1, r7F7F
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andc rWORD1, rTMP2, rTMP1
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andc rTMP3, rTMP2, rTMP1
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/* When we get to here, rSTR points to the first word in the string that
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contains a zero byte, and the most significant set bit in rWORD1 is in that
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byte. */
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contains a zero byte, and rTMP3 has 0x80 for bytes that are zero,
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and 0x00 otherwise. */
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L(done0):
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cntlzw rTMP3, rWORD1
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cntlzw rTMP3, rTMP3
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subf rTMP1, rRTN, rSTR
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srwi rTMP3, rTMP3, 3
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add rRTN, rTMP1, rTMP3
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blr
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#else
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L(done0):
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addi rTMP1, rTMP3, -1 /* Form a mask from trailing zeros. */
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andc rTMP1, rTMP1, rTMP3
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cntlzw rTMP1, rTMP1 /* Count bits not in the mask. */
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subf rTMP3, rRTN, rSTR
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subfic rTMP1, rTMP1, 32-7
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srwi rTMP1, rTMP1, 3
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add rRTN, rTMP1, rTMP3
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blr
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L(done1):
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addi rTMP3, rTMP1, -1
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andc rTMP3, rTMP3, rTMP1
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cntlzw rTMP3, rTMP3
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subf rTMP1, rRTN, rSTR
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subfic rTMP3, rTMP3, 32-7-32
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srawi rTMP3, rTMP3, 3
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add rRTN, rTMP1, rTMP3
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blr
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#endif
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END (strlen)
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libc_hidden_builtin_def (strlen)
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@ -30,7 +30,11 @@ ENTRY (strlen)
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with cmpb. */
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li r5,-1 /* MASK = 0xffffffffffffffff. */
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ld r12,0(r4) /* Load doubleword from memory. */
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#ifdef __LITTLE_ENDIAN__
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sld r5,r5,r6
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#else
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srd r5,r5,r6 /* MASK = MASK >> padding. */
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#endif
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orc r9,r12,r5 /* Mask bits that are not part of the string. */
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cmpb r10,r9,r0 /* Check for null bytes in DWORD1. */
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cmpdi cr7,r10,0 /* If r10 == 0, no null's have been found. */
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@ -48,9 +52,6 @@ ENTRY (strlen)
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cmpb r10,r12,r0
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cmpdi cr7,r10,0
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bne cr7,L(done)
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b L(loop) /* We branch here (rather than falling through)
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to skip the nops due to heavy alignment
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of the loop below. */
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/* Main loop to look for the end of the string. Since it's a
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small loop (< 8 instructions), align it to 32-bytes. */
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@ -87,9 +88,15 @@ L(loop):
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0xff in the same position as the null byte in the original
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doubleword from the string. Use that to calculate the length. */
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L(done):
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cntlzd r0,r10 /* Count leading zeroes before the match. */
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#ifdef __LITTLE_ENDIAN__
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addi r9, r10, -1 /* Form a mask from trailing zeros. */
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andc r9, r9, r10
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popcntd r0, r9 /* Count the bits in the mask. */
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#else
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cntlzd r0,r10 /* Count leading zeros before the match. */
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#endif
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subf r5,r3,r4
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srdi r0,r0,3 /* Convert leading zeroes to bytes. */
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srdi r0,r0,3 /* Convert leading/trailing zeros to bytes. */
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add r3,r5,r0 /* Compute final length. */
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blr
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END (strlen)
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@ -29,7 +29,12 @@
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1 is subtracted you get a value in the range 0x00-0x7f, none of which
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have their high bit set. The expression here is
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(x + 0xfefefeff) & ~(x | 0x7f7f7f7f), which gives 0x00000000 when
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there were no 0x00 bytes in the word.
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there were no 0x00 bytes in the word. You get 0x80 in bytes that
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match, but possibly false 0x80 matches in the next more significant
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byte to a true match due to carries. For little-endian this is
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of no consequence since the least significant match is the one
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we're interested in, but big-endian needs method 2 to find which
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byte matches.
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2) Given a word 'x', we can test to see _which_ byte was zero by
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calculating ~(((x & 0x7f7f7f7f) + 0x7f7f7f7f) | x | 0x7f7f7f7f).
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@ -62,7 +67,7 @@
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Answer:
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1) Added a Data Cache Block Touch early to prefetch the first 128
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byte cache line. Adding dcbt instructions to the loop would not be
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effective since most strings will be shorter than the cache line.*/
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effective since most strings will be shorter than the cache line. */
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/* Some notes on register usage: Under the SVR4 ABI, we can use registers
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0 and 3 through 12 (so long as we don't call any procedures) without
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@ -78,7 +83,7 @@
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ENTRY (strlen)
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CALL_MCOUNT 1
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#define rTMP1 r0
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#define rTMP4 r0
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#define rRTN r3 /* incoming STR arg, outgoing result */
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#define rSTR r4 /* current string position */
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#define rPADN r5 /* number of padding bits we prepend to the
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@ -88,9 +93,9 @@ ENTRY (strlen)
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#define rWORD1 r8 /* current string doubleword */
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#define rWORD2 r9 /* next string doubleword */
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#define rMASK r9 /* mask for first string doubleword */
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#define rTMP2 r10
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#define rTMP3 r11
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#define rTMP4 r12
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#define rTMP1 r10
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#define rTMP2 r11
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#define rTMP3 r12
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dcbt 0,rRTN
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clrrdi rSTR, rRTN, 3
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@ -100,30 +105,36 @@ ENTRY (strlen)
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addi r7F7F, r7F7F, 0x7f7f
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li rMASK, -1
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insrdi r7F7F, r7F7F, 32, 0
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/* That's the setup done, now do the first pair of doublewords.
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We make an exception and use method (2) on the first two doublewords,
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to reduce overhead. */
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/* We use method (2) on the first two doublewords, because rFEFE isn't
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required which reduces setup overhead. Also gives a faster return
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for small strings on big-endian due to needing to recalculate with
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method (2) anyway. */
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#ifdef __LITTLE_ENDIAN__
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sld rMASK, rMASK, rPADN
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#else
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srd rMASK, rMASK, rPADN
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#endif
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and rTMP1, r7F7F, rWORD1
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or rTMP2, r7F7F, rWORD1
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lis rFEFE, -0x101
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add rTMP1, rTMP1, r7F7F
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addi rFEFE, rFEFE, -0x101
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nor rTMP1, rTMP2, rTMP1
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and. rWORD1, rTMP1, rMASK
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nor rTMP3, rTMP2, rTMP1
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and. rTMP3, rTMP3, rMASK
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mtcrf 0x01, rRTN
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bne L(done0)
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sldi rTMP1, rFEFE, 32
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add rFEFE, rFEFE, rTMP1
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sldi rTMP1, rFEFE, 32
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add rFEFE, rFEFE, rTMP1
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/* Are we now aligned to a doubleword boundary? */
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bt 28, L(loop)
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/* Handle second doubleword of pair. */
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/* Perhaps use method (1) here for little-endian, saving one instruction? */
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ldu rWORD1, 8(rSTR)
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and rTMP1, r7F7F, rWORD1
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or rTMP2, r7F7F, rWORD1
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add rTMP1, rTMP1, r7F7F
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nor. rWORD1, rTMP2, rTMP1
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nor. rTMP3, rTMP2, rTMP1
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bne L(done0)
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/* The loop. */
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@ -137,28 +148,52 @@ L(loop):
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add rTMP3, rFEFE, rWORD2
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nor rTMP4, r7F7F, rWORD2
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bne L(done1)
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and. rTMP1, rTMP3, rTMP4
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and. rTMP3, rTMP3, rTMP4
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beq L(loop)
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#ifndef __LITTLE_ENDIAN__
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and rTMP1, r7F7F, rWORD2
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add rTMP1, rTMP1, r7F7F
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andc rWORD1, rTMP4, rTMP1
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andc rTMP3, rTMP4, rTMP1
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b L(done0)
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L(done1):
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and rTMP1, r7F7F, rWORD1
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subi rSTR, rSTR, 8
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add rTMP1, rTMP1, r7F7F
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andc rWORD1, rTMP2, rTMP1
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andc rTMP3, rTMP2, rTMP1
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/* When we get to here, rSTR points to the first doubleword in the string that
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contains a zero byte, and the most significant set bit in rWORD1 is in that
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byte. */
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contains a zero byte, and rTMP3 has 0x80 for bytes that are zero, and 0x00
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otherwise. */
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L(done0):
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cntlzd rTMP3, rWORD1
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cntlzd rTMP3, rTMP3
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subf rTMP1, rRTN, rSTR
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srdi rTMP3, rTMP3, 3
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add rRTN, rTMP1, rTMP3
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blr
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#else
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L(done0):
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addi rTMP1, rTMP3, -1 /* Form a mask from trailing zeros. */
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andc rTMP1, rTMP1, rTMP3
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cntlzd rTMP1, rTMP1 /* Count bits not in the mask. */
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subf rTMP3, rRTN, rSTR
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subfic rTMP1, rTMP1, 64-7
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srdi rTMP1, rTMP1, 3
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add rRTN, rTMP1, rTMP3
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blr
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L(done1):
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addi rTMP3, rTMP1, -1
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andc rTMP3, rTMP3, rTMP1
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cntlzd rTMP3, rTMP3
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subf rTMP1, rRTN, rSTR
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subfic rTMP3, rTMP3, 64-7-64
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sradi rTMP3, rTMP3, 3
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add rRTN, rTMP1, rTMP3
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blr
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#endif
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END (strlen)
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libc_hidden_builtin_def (strlen)
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