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powerpc: POWER7 strcpy optimization for unaligned strings
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This patch optimizes strcpy for ppc64/power7 for unaligned source or
destination address.  The source or destination address is aligned
to doubleword and data is shifted based on the alignment and
added with the previous loaded data to be written as a doubleword.
For each load, cmpb instruction is used for faster null check.

The word aligned optimization is also removed, since the new unaligned
code path shows better results handling word-aligned strings.

More combination of unaligned inputs is also added in benchtest
to measure the improvement.The new optimization shows 2 to 80% of
performance improvement for longer string though it does not show
big difference on string size less than 16 due to additional checks.
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Rajalakshmi Srinivasaraghavan authored and Adhemerval Zanella committed Dec 31, 2014
1 parent 4a3d399 commit f59ad97
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7 changes: 7 additions & 0 deletions ChangeLog
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Original file line number Diff line number Diff line change
@@ -1,3 +1,10 @@
2014-12-31 Rajalakshmi Srinivasaraghavan <raji@linux.vnet.ibm.com>
Adhemerval Zanella <azanella@linux.vnet.ibm.com>

* sysdeps/powerpc/powerpc64/power7/strcpy.S (strcpy): Optimize unaligned
path.
* benchtests/bench-strcpy.c (test_main): Add more unaligned inputs.

2014-12-31 Joseph Myers <joseph@codesourcery.com>

* sysdeps/powerpc/bits/fenvinline.h (fegetround): Rename macro to
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16 changes: 16 additions & 0 deletions benchtests/bench-strcpy.c
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Original file line number Diff line number Diff line change
Expand Up @@ -171,6 +171,22 @@ test_main (void)
do_test (i, i, 8 << i, BIG_CHAR);
}

for (i = 16; i <= 512; i+=4)
{
do_test (0, 4, i, SMALL_CHAR);
do_test (4, 0, i, BIG_CHAR);
do_test (4, 4, i, SMALL_CHAR);
do_test (2, 2, i, BIG_CHAR);
do_test (2, 6, i, SMALL_CHAR);
do_test (6, 2, i, BIG_CHAR);
do_test (1, 7, i, SMALL_CHAR);
do_test (7, 1, i, BIG_CHAR);
do_test (3, 4, i, SMALL_CHAR);
do_test (4, 3, i, BIG_CHAR);
do_test (5, 7, i, SMALL_CHAR);
do_test (7, 5, i, SMALL_CHAR);
}

return ret;
}

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327 changes: 245 additions & 82 deletions sysdeps/powerpc/powerpc64/power7/strcpy.S
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Original file line number Diff line number Diff line change
Expand Up @@ -31,8 +31,6 @@
if (((((uintptr_t)dst & 0x7UL) == 0) && ((uintptr_t)src & 0x7UL) == 0))
goto aligned_doubleword_copy;
if (((((uintptr_t)dst & 0x3UL) == 0) && ((uintptr_t)src & 0x3UL) == 0))
goto aligned_word_copy;
if (((uintptr_t)dst & 0x7UL) == ((uintptr_t)src & 0x7UL))
goto same_alignment;
goto unaligned;
Expand Down Expand Up @@ -70,9 +68,18 @@ EALIGN (FUNC_NAME, 4, 0)
#endif
or rTMP, rSRC, rRTN
clrldi. rTMP, rTMP, 61
bne L(check_word_alignment)
bne L(check_alignment)
b L(aligned_doubleword_copy)

.align 4
L(check_alignment):
rldicl rRTNAL, rRTN, 0, 61
rldicl rSRCAL, rSRC, 0, 61
cmpld cr7, rSRCAL, rRTNAL
beq cr7, L(same_alignment)
b L(unaligned)

.align 4
L(same_alignment):
/* Src and dst with same alignment: align both to doubleword. */
mr rALCNT, rRTN
Expand Down Expand Up @@ -180,93 +187,249 @@ L(g1):
#endif
blr

L(check_word_alignment):
clrldi. rTMP, rTMP, 62
beq L(aligned_word_copy)
rldicl rRTNAL, rRTN, 0, 61
rldicl rSRCAL, rSRC, 0, 61
cmpld cr7, rSRCAL, rRTNAL
beq cr7, L(same_alignment)
b L(unaligned)

/* For word aligned memory, operate using word load and stores. */
.align 4
L(aligned_word_copy):
li rMASK, 0
addi rRTN, rRTN, -4
lwz rWORD, 0(rSRC)
b L(g5)
L(unaligned):
cmpdi rSRCAL, 0 /* Check src alignment */
beq L(srcaligndstunalign)
/* src is unaligned */
rlwinm r10, rSRC, 3,26,28 /* Calculate padding. */
clrrdi rSRC, rSRC, 3 /* Align the addr to dw boundary */
ld rWORD, 0(rSRC) /* Load doubleword from memory. */
li rTMP, 0
/* Discard bits not part of the string */
#ifdef __LITTLE_ENDIAN__
srd rALT, rWORD, r10
#else
sld rALT, rWORD, r10
#endif
cmpb rTMP, rALT, rTMP /* Compare each byte against null */
/* Discard bits not part of the string */
#ifdef __LITTLE_ENDIAN__
sld rTMP, rTMP, r10
#else
srd rTMP, rTMP, r10
#endif
cmpdi rTMP, 0
bne L(bytebybyte) /* if it has null, copy byte by byte */
subfic r8, r9, 8
rlwinm r5, rRTN, 3,26,28 /* Calculate padding in bits. */
rldicl r9, rRTN, 0, 61 /* Calculate padding in bytes. */
addi rRTN, rRTN, -1

.align 4
L(g3): lwzu rALT, 4(rSRC)
stwu rWORD, 4(rRTN)
cmpb rTMP, rALT, rMASK
cmpwi rTMP, 0
bne L(g4)
lwzu rWORD, 4(rSRC)
stwu rALT, 4(rRTN)
L(g5): cmpb rTMP, rWORD, rMASK
cmpwi rTMP, 0 /* If rTMP is 0, no null in word. */
beq L(g3)

mr rALT, rWORD
/* We've hit the end of the string. Do the rest byte-by-byte. */
L(g4):
cmpdi r5, 0 /* check dest alignment */
beq L(srcunaligndstalign)

/* both src and dst unaligned */
#ifdef __LITTLE_ENDIAN__
rlwinm. rTMP, rALT, 0, 24, 31
stbu rALT, 4(rRTN)
beqlr-
rlwinm. rTMP, rALT, 24, 24, 31
stbu rTMP, 1(rRTN)
beqlr-
rlwinm. rTMP, rALT, 16, 24, 31
stbu rTMP, 1(rRTN)
beqlr-
rlwinm rTMP, rALT, 8, 24, 31
stbu rTMP, 1(rRTN)
sld rWORD, rALT, r10
mr r11, r10
addi r11, r11, -8 /* Adjust byte pointer on loaded dw */
#else
rlwinm. rTMP, rALT, 8, 24, 31
stbu rTMP, 4(rRTN)
beqlr
rlwinm. rTMP, rALT, 16, 24, 31
stbu rTMP, 1(rRTN)
beqlr
rlwinm. rTMP, rALT, 24, 24, 31
stbu rTMP, 1(rRTN)
beqlr
stbu rALT, 1(rRTN)
srd rWORD, rALT, r10
subfic r11, r10, 64
#endif
blr
/* dst alignment is greater then src alignment? */
cmpd cr7, r5, r10
blt cr7, L(dst_align_small)
/* src alignment is less than dst */

/* Oh well. In this case, we just do a byte-by-byte copy. */
.align 4
L(unaligned):
lbz rWORD, 0(rSRC)
addi rRTN, rRTN, -1
cmpdi rWORD, 0
beq L(u2)

.align 5
L(u0): lbzu rALT, 1(rSRC)
stbu rWORD, 1(rRTN)
cmpdi rALT, 0
beq L(u1)
lbzu rWORD, 1(rSRC)
/* Calculate the dst alignment differnce */
subfic rALT, r9, 8
mtctr rALT

/* Write till dst is aligned */
cmpdi rTMP, rALT, 4
blt L(storebyte1) /* less than 4, store byte by byte */
beq L(equal1) /* if its 4, store word */
addi rTMP, rALT, -4 /* greater than 4, so stb and stw */
mtctr rTMP
L(storebyte1):
#ifdef __LITTLE_ENDIAN__
addi r11, r11, 8 /* Adjust byte pointer on loaded dw */
#else
addi r11, r11, -8
#endif
srd rALT, rWORD, r11
stbu rALT, 1(rRTN)
bdnz L(storebyte1)

subfic rALT, r9, 8 /* Check the remaining bytes */
cmpdi rTMP, rALT, 4
blt L(proceed)

.align 4
L(equal1):
#ifdef __LITTLE_ENDIAN__
addi r11, r11, 8 /* Adjust byte pointer on loaded dw */
srd rALT, rWORD, r11
#else
subfic r11, r11, 64
sld rALT, rWORD, r11
srdi rALT, rALT, 32
#endif
stw rALT, 1(rRTN)
addi rRTN, rRTN, 4

L(proceed):
mr rALT, rWORD
/* calculate the Left over bytes to be written */
subfic r11, r10, 64
subfic r5, r5, 64
subf r5, r5, r11 /* remaining bytes on second dw */
subfic r10, r5, 64 /* remaining bytes on first dw */
subfic r9, r9, 8
subf r8, r9, r8 /* recalculate padding */
L(srcunaligndstalign):
addi rRTN, rRTN, 1
subfic r5, r10, 64 /* remaining bytes on second dw */
addi rSRC, rSRC, 8
li rTMP,0
b L(storedouble)

.align 4
L(dst_align_small):
mtctr r8
/* Write till src is aligned */
L(storebyte2):
#ifdef __LITTLE_ENDIAN__
addi r11, r11, 8 /* Adjust byte pointer on dw */
#else
addi r11, r11, -8
#endif
srd rALT, rWORD, r11
stbu rALT, 1(rRTN)
cmpdi rWORD, 0
beq L(u2)
lbzu rALT, 1(rSRC)
stbu rWORD, 1(rRTN)
cmpdi rALT, 0
beq L(u1)
lbzu rWORD, 1(rSRC)
bdnz L(storebyte2)

addi rSRC, rSRC, 8 /* Increment src pointer */
addi rRTN, rRTN, 1 /* Increment dst pointer */
rldicl r8, rRTN, 0, 61 /* Recalculate padding */

/* src is aligned */
L(srcaligndstunalign):
ld rWORD, 0(rSRC)
mr rALT, rWORD
li rTMP, 0 /* Check null */
cmpb rTMP, rWORD, rTMP
cmpdi rTMP, 0
bne L(bytebybyte) /* Do byte by byte if there is NULL */
rlwinm r5, rRTN, 3,26,28 /* Calculate padding */
addi rRTN, rRTN, -1
subfic r10, r8, 8
/* write byte by byte till aligned */
#ifdef __LITTLE_ENDIAN__
li r11, -8
#else
li r11, 64
#endif
mtctr r10
cmpdi rTMP, r10, 4
blt L(storebyte)
beq L(equal)
addi rTMP, r10, -4
mtctr rTMP
L(storebyte):
#ifdef __LITTLE_ENDIAN__
addi r11, r11, 8 /* Adjust byte pointer on dw */
#else
addi r11, r11, -8
#endif
srd rALT, rWORD, r11
stbu rALT, 1(rRTN)
cmpdi rWORD, 0
bne L(u0)
L(u2): stbu rWORD, 1(rRTN)
blr
L(u1): stbu rALT, 1(rRTN)
blr
bdnz L(storebyte)

cmpdi rTMP, r10, 4
blt L(align)

.align 4
L(equal):
#ifdef __LITTLE_ENDIAN__
addi r11, r11, 8
srd rALT, rWORD, r11
#else
subfic r11, r11, 64
sld rALT, rWORD, r11
srdi rALT, rALT, 32
#endif
stw rALT, 1(rRTN)
addi rRTN, rRTN, 4
L(align):
addi rRTN, rRTN, 1
addi rSRC, rSRC, 8 /* Increment src pointer */
subfic r10, r5, 64
li rTMP, 0
/* dst addr aligned to 8 */
L(storedouble):
ld rALT, 0(rSRC) /* load next dw */
cmpb rTMP, rALT, rTMP
cmpdi rTMP, 0 /* check for null on each new dw */
bne L(null)
#ifdef __LITTLE_ENDIAN__
srd r9, rWORD, r10 /* bytes from first dw */
sld r11, rALT, r5 /* bytes from second dw */
#else
sld r9, rWORD, r10
srd r11, rALT, r5
#endif
or r11, r9, r11 /* make as a single dw */
std r11, 0(rRTN) /* store as std on aligned addr */
mr rWORD, rALT /* still few bytes left to be written */
addi rRTN, rRTN, 8 /* increment dst addr */
addi rSRC, rSRC, 8 /* increment src addr */
b L(storedouble) /* Loop till NULL */

.align 4

/* We've hit the end of the string. Do the rest byte-by-byte. */
L(null):
addi rRTN, rRTN, -1
mr r10, r5
mtctr r8
#ifdef __LITTLE_ENDIAN__
subfic r10, r10, 64
addi r10, r10, -8
#endif
cmpdi rTMP, r8, 4
blt L(loop)

/* we can still use stw if leftover >= 4*/
#ifdef __LITTLE_ENDIAN__
addi r10, r10, 8
srd r11, rWORD, r10
#else
subfic r10, r10, 64
sld r11, rWORD, r10
srdi r11, r11, 32
#endif
stw r11, 1(rRTN)
addi rRTN, rRTN, 4

beq L(bytebybyte1)
addi r10, r10, 32
#ifdef __LITTLE_ENDIAN__
addi r10, r10, -8
#else
subfic r10, r10, 64
#endif
addi rTMP, r8, -4
mtctr rTMP
/* remaining byte by byte part of first dw */
L(loop):
#ifdef __LITTLE_ENDIAN__
addi r10, r10, 8
#else
addi r10, r10, -8
#endif
srd rTMP, rWORD, r10
stbu rTMP, 1(rRTN)
bdnz L(loop)

L(bytebybyte1):
addi rRTN, rRTN, 1
/* remaining byte by byte part of second dw */
L(bytebybyte):
addi rRTN, rRTN, -8
b L(g1)

END (FUNC_NAME)

#ifndef USE_AS_STPCPY
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