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commit df5de87260dba479873b2850bbe5c0b81c2376f6
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Author: Noah Goldstein <goldstein.w.n@gmail.com>
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Date: Fri Apr 15 12:28:01 2022 -0500
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x86: Cleanup page cross code in memcmp-avx2-movbe.S
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Old code was both inefficient and wasted code size. New code (-62
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bytes) and comparable or better performance in the page cross case.
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geometric_mean(N=20) of page cross cases New / Original: 0.960
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size, align0, align1, ret, New Time/Old Time
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1, 4095, 0, 0, 1.001
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1, 4095, 0, 1, 0.999
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1, 4095, 0, -1, 1.0
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2, 4094, 0, 0, 1.0
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2, 4094, 0, 1, 1.0
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2, 4094, 0, -1, 1.0
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3, 4093, 0, 0, 1.0
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3, 4093, 0, 1, 1.0
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3, 4093, 0, -1, 1.0
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4, 4092, 0, 0, 0.987
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4, 4092, 0, 1, 1.0
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4, 4092, 0, -1, 1.0
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5, 4091, 0, 0, 0.984
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5, 4091, 0, 1, 1.002
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5, 4091, 0, -1, 1.005
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6, 4090, 0, 0, 0.993
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6, 4090, 0, 1, 1.001
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6, 4090, 0, -1, 1.003
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7, 4089, 0, 0, 0.991
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7, 4089, 0, 1, 1.0
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7, 4089, 0, -1, 1.001
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8, 4088, 0, 0, 0.875
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8, 4088, 0, 1, 0.881
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8, 4088, 0, -1, 0.888
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9, 4087, 0, 0, 0.872
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9, 4087, 0, 1, 0.879
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9, 4087, 0, -1, 0.883
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10, 4086, 0, 0, 0.878
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10, 4086, 0, 1, 0.886
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10, 4086, 0, -1, 0.873
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11, 4085, 0, 0, 0.878
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11, 4085, 0, 1, 0.881
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11, 4085, 0, -1, 0.879
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12, 4084, 0, 0, 0.873
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12, 4084, 0, 1, 0.889
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12, 4084, 0, -1, 0.875
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13, 4083, 0, 0, 0.873
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13, 4083, 0, 1, 0.863
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13, 4083, 0, -1, 0.863
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14, 4082, 0, 0, 0.838
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14, 4082, 0, 1, 0.869
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14, 4082, 0, -1, 0.877
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15, 4081, 0, 0, 0.841
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15, 4081, 0, 1, 0.869
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15, 4081, 0, -1, 0.876
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16, 4080, 0, 0, 0.988
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16, 4080, 0, 1, 0.99
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16, 4080, 0, -1, 0.989
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17, 4079, 0, 0, 0.978
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17, 4079, 0, 1, 0.981
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17, 4079, 0, -1, 0.98
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18, 4078, 0, 0, 0.981
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18, 4078, 0, 1, 0.98
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18, 4078, 0, -1, 0.985
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19, 4077, 0, 0, 0.977
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19, 4077, 0, 1, 0.979
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19, 4077, 0, -1, 0.986
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20, 4076, 0, 0, 0.977
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20, 4076, 0, 1, 0.986
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20, 4076, 0, -1, 0.984
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21, 4075, 0, 0, 0.977
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21, 4075, 0, 1, 0.983
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21, 4075, 0, -1, 0.988
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22, 4074, 0, 0, 0.983
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22, 4074, 0, 1, 0.994
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22, 4074, 0, -1, 0.993
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23, 4073, 0, 0, 0.98
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23, 4073, 0, 1, 0.992
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23, 4073, 0, -1, 0.995
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24, 4072, 0, 0, 0.989
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24, 4072, 0, 1, 0.989
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24, 4072, 0, -1, 0.991
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25, 4071, 0, 0, 0.99
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25, 4071, 0, 1, 0.999
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25, 4071, 0, -1, 0.996
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26, 4070, 0, 0, 0.993
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26, 4070, 0, 1, 0.995
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26, 4070, 0, -1, 0.998
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27, 4069, 0, 0, 0.993
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27, 4069, 0, 1, 0.999
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27, 4069, 0, -1, 1.0
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28, 4068, 0, 0, 0.997
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28, 4068, 0, 1, 1.0
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28, 4068, 0, -1, 0.999
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29, 4067, 0, 0, 0.996
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29, 4067, 0, 1, 0.999
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29, 4067, 0, -1, 0.999
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30, 4066, 0, 0, 0.991
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30, 4066, 0, 1, 1.001
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30, 4066, 0, -1, 0.999
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31, 4065, 0, 0, 0.988
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31, 4065, 0, 1, 0.998
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31, 4065, 0, -1, 0.998
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Reviewed-by: H.J. Lu <hjl.tools@gmail.com>
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(cherry picked from commit 23102686ec67b856a2d4fd25ddaa1c0b8d175c4f)
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diff --git a/sysdeps/x86_64/multiarch/memcmp-avx2-movbe.S b/sysdeps/x86_64/multiarch/memcmp-avx2-movbe.S
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index 2621ec907aedb781..ec9cf0852edf216d 100644
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--- a/sysdeps/x86_64/multiarch/memcmp-avx2-movbe.S
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+++ b/sysdeps/x86_64/multiarch/memcmp-avx2-movbe.S
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@@ -429,22 +429,21 @@ L(page_cross_less_vec):
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# ifndef USE_AS_WMEMCMP
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cmpl $8, %edx
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jae L(between_8_15)
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+ /* Fall through for [4, 7]. */
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cmpl $4, %edx
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- jae L(between_4_7)
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+ jb L(between_2_3)
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- /* Load as big endian to avoid branches. */
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- movzwl (%rdi), %eax
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- movzwl (%rsi), %ecx
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- shll $8, %eax
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- shll $8, %ecx
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- bswap %eax
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- bswap %ecx
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- movzbl -1(%rdi, %rdx), %edi
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- movzbl -1(%rsi, %rdx), %esi
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- orl %edi, %eax
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- orl %esi, %ecx
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- /* Subtraction is okay because the upper 8 bits are zero. */
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- subl %ecx, %eax
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+ movbe (%rdi), %eax
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+ movbe (%rsi), %ecx
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+ shlq $32, %rax
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+ shlq $32, %rcx
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+ movbe -4(%rdi, %rdx), %edi
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+ movbe -4(%rsi, %rdx), %esi
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+ orq %rdi, %rax
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+ orq %rsi, %rcx
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+ subq %rcx, %rax
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+ /* Fast path for return zero. */
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+ jnz L(ret_nonzero)
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/* No ymm register was touched. */
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ret
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@@ -457,9 +456,33 @@ L(one_or_less):
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/* No ymm register was touched. */
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ret
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+ .p2align 4,, 5
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+L(ret_nonzero):
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+ sbbl %eax, %eax
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+ orl $1, %eax
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+ /* No ymm register was touched. */
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+ ret
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+
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+ .p2align 4,, 2
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+L(zero):
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+ xorl %eax, %eax
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+ /* No ymm register was touched. */
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+ ret
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+
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.p2align 4
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L(between_8_15):
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-# endif
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+ movbe (%rdi), %rax
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+ movbe (%rsi), %rcx
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+ subq %rcx, %rax
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+ jnz L(ret_nonzero)
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+ movbe -8(%rdi, %rdx), %rax
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+ movbe -8(%rsi, %rdx), %rcx
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+ subq %rcx, %rax
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+ /* Fast path for return zero. */
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+ jnz L(ret_nonzero)
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+ /* No ymm register was touched. */
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+ ret
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+# else
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/* If USE_AS_WMEMCMP fall through into 8-15 byte case. */
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vmovq (%rdi), %xmm1
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vmovq (%rsi), %xmm2
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@@ -475,16 +498,13 @@ L(between_8_15):
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VPCMPEQ %xmm1, %xmm2, %xmm2
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vpmovmskb %xmm2, %eax
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subl $0xffff, %eax
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+ /* Fast path for return zero. */
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jnz L(return_vec_0)
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/* No ymm register was touched. */
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ret
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+# endif
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- .p2align 4
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-L(zero):
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- xorl %eax, %eax
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- ret
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-
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- .p2align 4
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+ .p2align 4,, 10
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L(between_16_31):
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/* From 16 to 31 bytes. No branch when size == 16. */
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vmovdqu (%rsi), %xmm2
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@@ -501,11 +521,17 @@ L(between_16_31):
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VPCMPEQ (%rdi), %xmm2, %xmm2
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vpmovmskb %xmm2, %eax
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subl $0xffff, %eax
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+ /* Fast path for return zero. */
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jnz L(return_vec_0)
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/* No ymm register was touched. */
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ret
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# ifdef USE_AS_WMEMCMP
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+ .p2align 4,, 2
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+L(zero):
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+ xorl %eax, %eax
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+ ret
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+
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.p2align 4
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L(one_or_less):
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jb L(zero)
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@@ -520,22 +546,20 @@ L(one_or_less):
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# else
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.p2align 4
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-L(between_4_7):
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- /* Load as big endian with overlapping movbe to avoid branches.
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- */
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- movbe (%rdi), %eax
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- movbe (%rsi), %ecx
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- shlq $32, %rax
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- shlq $32, %rcx
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- movbe -4(%rdi, %rdx), %edi
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- movbe -4(%rsi, %rdx), %esi
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- orq %rdi, %rax
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- orq %rsi, %rcx
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- subq %rcx, %rax
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- jz L(zero_4_7)
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- sbbl %eax, %eax
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- orl $1, %eax
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-L(zero_4_7):
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+L(between_2_3):
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+ /* Load as big endian to avoid branches. */
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+ movzwl (%rdi), %eax
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+ movzwl (%rsi), %ecx
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+ bswap %eax
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+ bswap %ecx
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+ shrl %eax
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+ shrl %ecx
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+ movzbl -1(%rdi, %rdx), %edi
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+ movzbl -1(%rsi, %rdx), %esi
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+ orl %edi, %eax
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+ orl %esi, %ecx
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+ /* Subtraction is okay because the upper bit is zero. */
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+ subl %ecx, %eax
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/* No ymm register was touched. */
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ret
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# endif
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