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This is an optimized memset for AArch64. Memset is split into 4 main cases:
small sets of up to 16 bytes, medium of 16..96 bytes which are fully unrolled. Large memsets of more than 96 bytes align the destination and use an unrolled loop processing 64 bytes per iteration. Memsets of zero of more than 256 use the dc zva instruction, and there are faster versions for the common ZVA sizes 64 or 128. STP of Q registers is used to reduce codesize without loss of performance. The speedup on test-memset is 1% on Cortex-A57 and 8% on Cortex-A53. * sysdeps/aarch64/memset.S (__memset): Rewrite of optimized memset.
This commit is contained in:
Wilco Dijkstra
parent
56290d6e76
commit
a8c5a2a952
@ -1,3 +1,8 @@
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2016-05-12 Wilco Dijkstra <wdijkstr@arm.com>
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* sysdeps/aarch64/memset.S (__memset):
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Rewrite of optimized memset.
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2016-05-12 Florian Weimer <fweimer@redhat.com>
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[BZ #19703]
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@ -16,213 +16,176 @@
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License along with the GNU C Library. If not, see
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<http://www.gnu.org/licenses/>. */
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#include <sysdep.h>
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/* Assumptions:
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*
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* ARMv8-a, AArch64
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* Unaligned accesses
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* ARMv8-a, AArch64, unaligned accesses
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*
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*/
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#include <sysdep.h>
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/* By default we assume that the DC instruction can be used to zero
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data blocks more efficiently. In some circumstances this might be
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unsafe, for example in an asymmetric multiprocessor environment with
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different DC clear lengths (neither the upper nor lower lengths are
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safe to use). The feature can be disabled by defining DONT_USE_DC.
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If code may be run in a virtualized environment, then define
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MAYBE_VIRT. This will cause the code to cache the system register
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values rather than re-reading them each call. */
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#define dstin x0
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#define val w1
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#define count x2
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#define tmp1 x3
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#define tmp1w w3
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#define tmp2 x4
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#define tmp2w w4
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#define zva_len_x x5
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#define zva_len w5
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#define zva_bits_x x6
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#define A_l x7
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#define A_lw w7
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#define dst x8
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#define tmp3w w9
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#define dstin x0
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#define val x1
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#define valw w1
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#define count x2
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#define dst x3
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#define dstend x4
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#define tmp1 x5
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#define tmp1w w5
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#define tmp2 x6
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#define tmp2w w6
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#define zva_len x7
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#define zva_lenw w7
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ENTRY_ALIGN (__memset, 6)
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mov dst, dstin /* Preserve return value. */
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ands A_lw, val, #255
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#ifndef DONT_USE_DC
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b.eq L(zero_mem)
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#endif
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orr A_lw, A_lw, A_lw, lsl #8
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orr A_lw, A_lw, A_lw, lsl #16
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orr A_l, A_l, A_l, lsl #32
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L(tail_maybe_long):
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cmp count, #64
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b.ge L(not_short)
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L(tail_maybe_tiny):
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cmp count, #15
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b.le L(tail15tiny)
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L(tail63):
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ands tmp1, count, #0x30
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b.eq L(tail15)
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add dst, dst, tmp1
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cmp tmp1w, #0x20
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b.eq 1f
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b.lt 2f
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stp A_l, A_l, [dst, #-48]
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1:
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stp A_l, A_l, [dst, #-32]
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2:
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stp A_l, A_l, [dst, #-16]
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dup v0.16B, valw
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add dstend, dstin, count
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L(tail15):
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and count, count, #15
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add dst, dst, count
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stp A_l, A_l, [dst, #-16] /* Repeat some/all of last store. */
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RET
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cmp count, 96
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b.hi L(set_long)
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cmp count, 16
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b.hs L(set_medium)
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mov val, v0.D[0]
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L(tail15tiny):
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/* Set up to 15 bytes. Does not assume earlier memory
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being set. */
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tbz count, #3, 1f
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str A_l, [dst], #8
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1:
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tbz count, #2, 1f
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str A_lw, [dst], #4
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1:
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tbz count, #1, 1f
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strh A_lw, [dst], #2
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1:
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tbz count, #0, 1f
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strb A_lw, [dst]
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1:
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RET
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/* Set 0..15 bytes. */
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tbz count, 3, 1f
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str val, [dstin]
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str val, [dstend, -8]
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ret
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nop
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1: tbz count, 2, 2f
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str valw, [dstin]
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str valw, [dstend, -4]
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ret
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2: cbz count, 3f
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strb valw, [dstin]
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tbz count, 1, 3f
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strh valw, [dstend, -2]
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3: ret
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/* Critical loop. Start at a new cache line boundary. Assuming
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* 64 bytes per line, this ensures the entire loop is in one line. */
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.p2align 6
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L(not_short):
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neg tmp2, dst
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ands tmp2, tmp2, #15
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b.eq 2f
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/* Bring DST to 128-bit (16-byte) alignment. We know that there's
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* more than that to set, so we simply store 16 bytes and advance by
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* the amount required to reach alignment. */
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sub count, count, tmp2
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stp A_l, A_l, [dst]
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add dst, dst, tmp2
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/* There may be less than 63 bytes to go now. */
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cmp count, #63
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b.le L(tail63)
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2:
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sub dst, dst, #16 /* Pre-bias. */
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sub count, count, #64
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1:
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stp A_l, A_l, [dst, #16]
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stp A_l, A_l, [dst, #32]
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stp A_l, A_l, [dst, #48]
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stp A_l, A_l, [dst, #64]!
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subs count, count, #64
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b.ge 1b
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tst count, #0x3f
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add dst, dst, #16
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b.ne L(tail63)
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RET
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/* Set 17..96 bytes. */
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L(set_medium):
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str q0, [dstin]
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tbnz count, 6, L(set96)
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str q0, [dstend, -16]
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tbz count, 5, 1f
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str q0, [dstin, 16]
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str q0, [dstend, -32]
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1: ret
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#ifndef DONT_USE_DC
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/* For zeroing memory, check to see if we can use the ZVA feature to
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* zero entire 'cache' lines. */
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L(zero_mem):
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mov A_l, #0
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cmp count, #63
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b.le L(tail_maybe_tiny)
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neg tmp2, dst
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ands tmp2, tmp2, #15
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b.eq 1f
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sub count, count, tmp2
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stp A_l, A_l, [dst]
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add dst, dst, tmp2
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cmp count, #63
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b.le L(tail63)
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1:
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/* For zeroing small amounts of memory, it's not worth setting up
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* the line-clear code. */
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cmp count, #128
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b.lt L(not_short)
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#ifdef MAYBE_VIRT
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/* For efficiency when virtualized, we cache the ZVA capability. */
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adrp tmp2, L(cache_clear)
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ldr zva_len, [tmp2, #:lo12:L(cache_clear)]
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tbnz zva_len, #31, L(not_short)
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cbnz zva_len, L(zero_by_line)
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.p2align 4
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/* Set 64..96 bytes. Write 64 bytes from the start and
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32 bytes from the end. */
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L(set96):
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str q0, [dstin, 16]
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stp q0, q0, [dstin, 32]
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stp q0, q0, [dstend, -32]
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ret
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.p2align 3
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nop
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L(set_long):
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and valw, valw, 255
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bic dst, dstin, 15
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str q0, [dstin]
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cmp count, 256
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ccmp valw, 0, 0, cs
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b.eq L(try_zva)
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L(no_zva):
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sub count, dstend, dst /* Count is 16 too large. */
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add dst, dst, 16
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sub count, count, 64 + 16 /* Adjust count and bias for loop. */
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1: stp q0, q0, [dst], 64
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stp q0, q0, [dst, -32]
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L(tail64):
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subs count, count, 64
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b.hi 1b
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2: stp q0, q0, [dstend, -64]
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stp q0, q0, [dstend, -32]
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ret
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.p2align 3
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L(try_zva):
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mrs tmp1, dczid_el0
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tbz tmp1, #4, 1f
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/* ZVA not available. Remember this for next time. */
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mov zva_len, #~0
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str zva_len, [tmp2, #:lo12:L(cache_clear)]
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b L(not_short)
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1:
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mov tmp3w, #4
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and zva_len, tmp1w, #15 /* Safety: other bits reserved. */
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lsl zva_len, tmp3w, zva_len
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str zva_len, [tmp2, #:lo12:L(cache_clear)]
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#else
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mrs tmp1, dczid_el0
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tbnz tmp1, #4, L(not_short)
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mov tmp3w, #4
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and zva_len, tmp1w, #15 /* Safety: other bits reserved. */
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lsl zva_len, tmp3w, zva_len
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#endif
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tbnz tmp1w, 4, L(no_zva)
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and tmp1w, tmp1w, 15
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cmp tmp1w, 4 /* ZVA size is 64 bytes. */
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b.ne L(zva_128)
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L(zero_by_line):
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/* Compute how far we need to go to become suitably aligned. We're
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* already at quad-word alignment. */
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cmp count, zva_len_x
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b.lt L(not_short) /* Not enough to reach alignment. */
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sub zva_bits_x, zva_len_x, #1
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neg tmp2, dst
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ands tmp2, tmp2, zva_bits_x
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b.eq 1f /* Already aligned. */
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/* Not aligned, check that there's enough to copy after alignment. */
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sub tmp1, count, tmp2
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cmp tmp1, #64
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ccmp tmp1, zva_len_x, #8, ge /* NZCV=0b1000 */
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b.lt L(not_short)
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/* We know that there's at least 64 bytes to zero and that it's safe
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* to overrun by 64 bytes. */
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mov count, tmp1
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2:
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stp A_l, A_l, [dst]
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stp A_l, A_l, [dst, #16]
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stp A_l, A_l, [dst, #32]
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subs tmp2, tmp2, #64
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stp A_l, A_l, [dst, #48]
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add dst, dst, #64
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b.ge 2b
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/* We've overrun a bit, so adjust dst downwards. */
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add dst, dst, tmp2
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1:
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sub count, count, zva_len_x
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3:
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dc zva, dst
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add dst, dst, zva_len_x
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subs count, count, zva_len_x
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b.ge 3b
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ands count, count, zva_bits_x
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b.ne L(tail_maybe_long)
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RET
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#ifdef MAYBE_VIRT
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.bss
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.p2align 2
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L(cache_clear):
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.space 4
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#endif
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#endif /* DONT_USE_DC */
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/* Write the first and last 64 byte aligned block using stp rather
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than using DC ZVA. This is faster on some cores.
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*/
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L(zva_64):
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str q0, [dst, 16]
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stp q0, q0, [dst, 32]
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bic dst, dst, 63
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stp q0, q0, [dst, 64]
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stp q0, q0, [dst, 96]
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sub count, dstend, dst /* Count is now 128 too large. */
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sub count, count, 128+64+64 /* Adjust count and bias for loop. */
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add dst, dst, 128
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nop
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1: dc zva, dst
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add dst, dst, 64
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subs count, count, 64
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b.hi 1b
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stp q0, q0, [dst, 0]
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stp q0, q0, [dst, 32]
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stp q0, q0, [dstend, -64]
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stp q0, q0, [dstend, -32]
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ret
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.p2align 3
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L(zva_128):
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cmp tmp1w, 5 /* ZVA size is 128 bytes. */
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b.ne L(zva_other)
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str q0, [dst, 16]
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stp q0, q0, [dst, 32]
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stp q0, q0, [dst, 64]
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stp q0, q0, [dst, 96]
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bic dst, dst, 127
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sub count, dstend, dst /* Count is now 128 too large. */
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sub count, count, 128+128 /* Adjust count and bias for loop. */
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add dst, dst, 128
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1: dc zva, dst
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add dst, dst, 128
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subs count, count, 128
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b.hi 1b
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stp q0, q0, [dstend, -128]
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stp q0, q0, [dstend, -96]
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stp q0, q0, [dstend, -64]
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stp q0, q0, [dstend, -32]
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ret
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L(zva_other):
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mov tmp2w, 4
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lsl zva_lenw, tmp2w, tmp1w
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add tmp1, zva_len, 64 /* Max alignment bytes written. */
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cmp count, tmp1
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blo L(no_zva)
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sub tmp2, zva_len, 1
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add tmp1, dst, zva_len
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add dst, dst, 16
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subs count, tmp1, dst /* Actual alignment bytes to write. */
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bic tmp1, tmp1, tmp2 /* Aligned dc zva start address. */
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beq 2f
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1: stp q0, q0, [dst], 64
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stp q0, q0, [dst, -32]
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subs count, count, 64
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b.hi 1b
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2: mov dst, tmp1
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sub count, dstend, tmp1 /* Remaining bytes to write. */
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subs count, count, zva_len
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b.lo 4f
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3: dc zva, dst
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add dst, dst, zva_len
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subs count, count, zva_len
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b.hs 3b
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4: add count, count, zva_len
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b L(tail64)
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END (__memset)
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weak_alias (__memset, memset)
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