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x86: Code cleanup in strchr-evex and comment justifying branch
Small code cleanup for size: -81 bytes.
Add comment justifying using a branch to do NULL/non-null return.
All string/memory tests pass and no regressions in benchtests.
geometric_mean(N=20) of all benchmarks New / Original: .985
Reviewed-by: H.J. Lu <hjl.tools@gmail.com>
(cherry picked from commit ec285ea904)
This commit is contained in:
Noah Goldstein
Sunil K Pandey
parent
3c55c20756
commit
dd6d3a0bbc
@ -30,6 +30,7 @@
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# ifdef USE_AS_WCSCHR
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# define VPBROADCAST vpbroadcastd
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# define VPCMP vpcmpd
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# define VPTESTN vptestnmd
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# define VPMINU vpminud
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# define CHAR_REG esi
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# define SHIFT_REG ecx
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@ -37,6 +38,7 @@
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# else
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# define VPBROADCAST vpbroadcastb
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# define VPCMP vpcmpb
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# define VPTESTN vptestnmb
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# define VPMINU vpminub
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# define CHAR_REG sil
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# define SHIFT_REG edx
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@ -61,13 +63,11 @@
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# define CHAR_PER_VEC (VEC_SIZE / CHAR_SIZE)
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.section .text.evex,"ax",@progbits
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ENTRY (STRCHR)
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ENTRY_P2ALIGN (STRCHR, 5)
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/* Broadcast CHAR to YMM0. */
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VPBROADCAST %esi, %YMM0
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movl %edi, %eax
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andl $(PAGE_SIZE - 1), %eax
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vpxorq %XMMZERO, %XMMZERO, %XMMZERO
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/* Check if we cross page boundary with one vector load.
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Otherwise it is safe to use an unaligned load. */
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cmpl $(PAGE_SIZE - VEC_SIZE), %eax
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@ -81,49 +81,35 @@ ENTRY (STRCHR)
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vpxorq %YMM1, %YMM0, %YMM2
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VPMINU %YMM2, %YMM1, %YMM2
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/* Each bit in K0 represents a CHAR or a null byte in YMM1. */
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VPCMP $0, %YMMZERO, %YMM2, %k0
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VPTESTN %YMM2, %YMM2, %k0
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kmovd %k0, %eax
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testl %eax, %eax
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jz L(aligned_more)
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tzcntl %eax, %eax
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# ifndef USE_AS_STRCHRNUL
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/* Found CHAR or the null byte. */
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cmp (%rdi, %rax, CHAR_SIZE), %CHAR_REG
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/* NB: Use a branch instead of cmovcc here. The expectation is
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that with strchr the user will branch based on input being
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null. Since this branch will be 100% predictive of the user
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branch a branch miss here should save what otherwise would
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be branch miss in the user code. Otherwise using a branch 1)
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saves code size and 2) is faster in highly predictable
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environments. */
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jne L(zero)
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# endif
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# ifdef USE_AS_WCSCHR
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/* NB: Multiply wchar_t count by 4 to get the number of bytes.
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*/
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leaq (%rdi, %rax, CHAR_SIZE), %rax
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# else
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addq %rdi, %rax
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# endif
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# ifndef USE_AS_STRCHRNUL
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/* Found CHAR or the null byte. */
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cmp (%rax), %CHAR_REG
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jne L(zero)
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# endif
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ret
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/* .p2align 5 helps keep performance more consistent if ENTRY()
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alignment % 32 was either 16 or 0. As well this makes the
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alignment % 32 of the loop_4x_vec fixed which makes tuning it
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easier. */
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.p2align 5
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L(first_vec_x3):
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tzcntl %eax, %eax
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# ifndef USE_AS_STRCHRNUL
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/* Found CHAR or the null byte. */
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cmp (VEC_SIZE * 3)(%rdi, %rax, CHAR_SIZE), %CHAR_REG
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jne L(zero)
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# endif
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/* NB: Multiply sizeof char type (1 or 4) to get the number of
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bytes. */
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leaq (VEC_SIZE * 3)(%rdi, %rax, CHAR_SIZE), %rax
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ret
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# ifndef USE_AS_STRCHRNUL
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L(zero):
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xorl %eax, %eax
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ret
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# endif
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.p2align 4
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.p2align 4,, 10
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L(first_vec_x4):
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# ifndef USE_AS_STRCHRNUL
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/* Check to see if first match was CHAR (k0) or null (k1). */
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@ -144,9 +130,18 @@ L(first_vec_x4):
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leaq (VEC_SIZE * 4)(%rdi, %rax, CHAR_SIZE), %rax
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ret
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# ifndef USE_AS_STRCHRNUL
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L(zero):
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xorl %eax, %eax
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ret
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# endif
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.p2align 4
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L(first_vec_x1):
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tzcntl %eax, %eax
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/* Use bsf here to save 1-byte keeping keeping the block in 1x
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fetch block. eax guranteed non-zero. */
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bsfl %eax, %eax
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# ifndef USE_AS_STRCHRNUL
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/* Found CHAR or the null byte. */
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cmp (VEC_SIZE)(%rdi, %rax, CHAR_SIZE), %CHAR_REG
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@ -158,7 +153,7 @@ L(first_vec_x1):
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leaq (VEC_SIZE)(%rdi, %rax, CHAR_SIZE), %rax
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ret
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.p2align 4
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.p2align 4,, 10
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L(first_vec_x2):
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# ifndef USE_AS_STRCHRNUL
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/* Check to see if first match was CHAR (k0) or null (k1). */
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@ -179,6 +174,21 @@ L(first_vec_x2):
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leaq (VEC_SIZE * 2)(%rdi, %rax, CHAR_SIZE), %rax
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ret
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.p2align 4,, 10
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L(first_vec_x3):
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/* Use bsf here to save 1-byte keeping keeping the block in 1x
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fetch block. eax guranteed non-zero. */
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bsfl %eax, %eax
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# ifndef USE_AS_STRCHRNUL
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/* Found CHAR or the null byte. */
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cmp (VEC_SIZE * 3)(%rdi, %rax, CHAR_SIZE), %CHAR_REG
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jne L(zero)
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# endif
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/* NB: Multiply sizeof char type (1 or 4) to get the number of
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bytes. */
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leaq (VEC_SIZE * 3)(%rdi, %rax, CHAR_SIZE), %rax
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ret
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.p2align 4
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L(aligned_more):
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/* Align data to VEC_SIZE. */
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@ -195,7 +205,7 @@ L(cross_page_continue):
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vpxorq %YMM1, %YMM0, %YMM2
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VPMINU %YMM2, %YMM1, %YMM2
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/* Each bit in K0 represents a CHAR or a null byte in YMM1. */
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VPCMP $0, %YMMZERO, %YMM2, %k0
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VPTESTN %YMM2, %YMM2, %k0
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kmovd %k0, %eax
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testl %eax, %eax
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jnz L(first_vec_x1)
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@ -206,7 +216,7 @@ L(cross_page_continue):
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/* Each bit in K0 represents a CHAR in YMM1. */
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VPCMP $0, %YMM1, %YMM0, %k0
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/* Each bit in K1 represents a CHAR in YMM1. */
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VPCMP $0, %YMM1, %YMMZERO, %k1
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VPTESTN %YMM1, %YMM1, %k1
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kortestd %k0, %k1
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jnz L(first_vec_x2)
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@ -215,7 +225,7 @@ L(cross_page_continue):
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vpxorq %YMM1, %YMM0, %YMM2
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VPMINU %YMM2, %YMM1, %YMM2
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/* Each bit in K0 represents a CHAR or a null byte in YMM1. */
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VPCMP $0, %YMMZERO, %YMM2, %k0
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VPTESTN %YMM2, %YMM2, %k0
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kmovd %k0, %eax
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testl %eax, %eax
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jnz L(first_vec_x3)
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@ -224,7 +234,7 @@ L(cross_page_continue):
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/* Each bit in K0 represents a CHAR in YMM1. */
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VPCMP $0, %YMM1, %YMM0, %k0
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/* Each bit in K1 represents a CHAR in YMM1. */
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VPCMP $0, %YMM1, %YMMZERO, %k1
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VPTESTN %YMM1, %YMM1, %k1
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kortestd %k0, %k1
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jnz L(first_vec_x4)
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@ -265,33 +275,33 @@ L(loop_4x_vec):
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VPMINU %YMM3, %YMM4, %YMM4
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VPMINU %YMM2, %YMM4, %YMM4{%k4}{z}
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VPCMP $0, %YMMZERO, %YMM4, %k1
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VPTESTN %YMM4, %YMM4, %k1
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kmovd %k1, %ecx
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subq $-(VEC_SIZE * 4), %rdi
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testl %ecx, %ecx
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jz L(loop_4x_vec)
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VPCMP $0, %YMMZERO, %YMM1, %k0
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VPTESTN %YMM1, %YMM1, %k0
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kmovd %k0, %eax
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testl %eax, %eax
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jnz L(last_vec_x1)
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VPCMP $0, %YMMZERO, %YMM2, %k0
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VPTESTN %YMM2, %YMM2, %k0
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kmovd %k0, %eax
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testl %eax, %eax
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jnz L(last_vec_x2)
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VPCMP $0, %YMMZERO, %YMM3, %k0
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VPTESTN %YMM3, %YMM3, %k0
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kmovd %k0, %eax
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/* Combine YMM3 matches (eax) with YMM4 matches (ecx). */
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# ifdef USE_AS_WCSCHR
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sall $8, %ecx
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orl %ecx, %eax
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tzcntl %eax, %eax
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bsfl %eax, %eax
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# else
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salq $32, %rcx
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orq %rcx, %rax
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tzcntq %rax, %rax
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bsfq %rax, %rax
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# endif
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# ifndef USE_AS_STRCHRNUL
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/* Check if match was CHAR or null. */
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@ -303,28 +313,28 @@ L(loop_4x_vec):
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leaq (VEC_SIZE * 2)(%rdi, %rax, CHAR_SIZE), %rax
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ret
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# ifndef USE_AS_STRCHRNUL
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L(zero_end):
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xorl %eax, %eax
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ret
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.p2align 4,, 8
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L(last_vec_x1):
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bsfl %eax, %eax
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# ifdef USE_AS_WCSCHR
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/* NB: Multiply wchar_t count by 4 to get the number of bytes.
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*/
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leaq (%rdi, %rax, CHAR_SIZE), %rax
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# else
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addq %rdi, %rax
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# endif
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.p2align 4
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L(last_vec_x1):
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tzcntl %eax, %eax
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# ifndef USE_AS_STRCHRNUL
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/* Check if match was null. */
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cmp (%rdi, %rax, CHAR_SIZE), %CHAR_REG
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cmp (%rax), %CHAR_REG
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jne L(zero_end)
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# endif
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/* NB: Multiply sizeof char type (1 or 4) to get the number of
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bytes. */
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leaq (%rdi, %rax, CHAR_SIZE), %rax
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ret
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.p2align 4
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.p2align 4,, 8
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L(last_vec_x2):
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tzcntl %eax, %eax
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bsfl %eax, %eax
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# ifndef USE_AS_STRCHRNUL
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/* Check if match was null. */
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cmp (VEC_SIZE)(%rdi, %rax, CHAR_SIZE), %CHAR_REG
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@ -336,7 +346,7 @@ L(last_vec_x2):
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ret
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/* Cold case for crossing page with first load. */
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.p2align 4
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.p2align 4,, 8
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L(cross_page_boundary):
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movq %rdi, %rdx
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/* Align rdi. */
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@ -346,9 +356,9 @@ L(cross_page_boundary):
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vpxorq %YMM1, %YMM0, %YMM2
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VPMINU %YMM2, %YMM1, %YMM2
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/* Each bit in K0 represents a CHAR or a null byte in YMM1. */
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VPCMP $0, %YMMZERO, %YMM2, %k0
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VPTESTN %YMM2, %YMM2, %k0
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kmovd %k0, %eax
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/* Remove the leading bits. */
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/* Remove the leading bits. */
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# ifdef USE_AS_WCSCHR
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movl %edx, %SHIFT_REG
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/* NB: Divide shift count by 4 since each bit in K1 represent 4
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@ -360,20 +370,24 @@ L(cross_page_boundary):
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/* If eax is zero continue. */
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testl %eax, %eax
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jz L(cross_page_continue)
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tzcntl %eax, %eax
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# ifndef USE_AS_STRCHRNUL
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/* Check to see if match was CHAR or null. */
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cmp (%rdx, %rax, CHAR_SIZE), %CHAR_REG
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jne L(zero_end)
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# endif
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bsfl %eax, %eax
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# ifdef USE_AS_WCSCHR
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/* NB: Multiply wchar_t count by 4 to get the number of
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bytes. */
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leaq (%rdx, %rax, CHAR_SIZE), %rax
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# else
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addq %rdx, %rax
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# endif
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# ifndef USE_AS_STRCHRNUL
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/* Check to see if match was CHAR or null. */
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cmp (%rax), %CHAR_REG
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je L(cross_page_ret)
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L(zero_end):
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xorl %eax, %eax
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L(cross_page_ret):
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# endif
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ret
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END (STRCHR)
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# endif
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#endif
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