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373 lines
9.4 KiB
373 lines
9.4 KiB
From a6fbf4d51e9ba8063c4f8331564892ead9c67344 Mon Sep 17 00:00:00 2001
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From: Noah Goldstein <goldstein.w.n@gmail.com>
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Date: Wed, 23 Mar 2022 16:57:16 -0500
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Subject: [PATCH] x86: Code cleanup in strchr-avx2 and comment justifying
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branch
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Content-type: text/plain; charset=UTF-8
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Small code cleanup for size: -53 bytes.
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Add comment justifying using a branch to do NULL/non-null return.
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All string/memory tests pass and no regressions in benchtests.
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geometric_mean(N=20) of all benchmarks Original / New: 1.00
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Reviewed-by: H.J. Lu <hjl.tools@gmail.com>
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---
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sysdeps/x86_64/multiarch/strchr-avx2.S | 204 +++++++++++++------------
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1 file changed, 107 insertions(+), 97 deletions(-)
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diff --git a/sysdeps/x86_64/multiarch/strchr-avx2.S b/sysdeps/x86_64/multiarch/strchr-avx2.S
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index 5884726b..89dd2bf7 100644
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--- a/sysdeps/x86_64/multiarch/strchr-avx2.S
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+++ b/sysdeps/x86_64/multiarch/strchr-avx2.S
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@@ -48,13 +48,13 @@
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# define PAGE_SIZE 4096
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.section SECTION(.text),"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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vmovd %esi, %xmm0
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movl %edi, %eax
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andl $(PAGE_SIZE - 1), %eax
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VPBROADCAST %xmm0, %ymm0
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- vpxor %xmm9, %xmm9, %xmm9
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+ vpxor %xmm1, %xmm1, %xmm1
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/* Check if we cross page boundary with one vector load. */
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cmpl $(PAGE_SIZE - VEC_SIZE), %eax
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@@ -62,37 +62,29 @@ ENTRY (STRCHR)
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/* Check the first VEC_SIZE bytes. Search for both CHAR and the
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null byte. */
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- vmovdqu (%rdi), %ymm8
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- VPCMPEQ %ymm8, %ymm0, %ymm1
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- VPCMPEQ %ymm8, %ymm9, %ymm2
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- vpor %ymm1, %ymm2, %ymm1
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- vpmovmskb %ymm1, %eax
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+ vmovdqu (%rdi), %ymm2
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+ VPCMPEQ %ymm2, %ymm0, %ymm3
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+ VPCMPEQ %ymm2, %ymm1, %ymm2
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+ vpor %ymm3, %ymm2, %ymm3
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+ vpmovmskb %ymm3, %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_REG
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- jne L(zero)
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-# endif
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- addq %rdi, %rax
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- VZEROUPPER_RETURN
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-
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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_x4):
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- tzcntl %eax, %eax
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- addq $(VEC_SIZE * 3 + 1), %rdi
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-# ifndef USE_AS_STRCHRNUL
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- /* Found CHAR or the null byte. */
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+ /* Found CHAR or the null byte. */
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cmp (%rdi, %rax), %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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addq %rdi, %rax
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- VZEROUPPER_RETURN
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+L(return_vzeroupper):
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+ ZERO_UPPER_VEC_REGISTERS_RETURN
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# ifndef USE_AS_STRCHRNUL
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L(zero):
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@@ -103,7 +95,8 @@ L(zero):
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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 to save code size. */
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+ bsfl %eax, %eax
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incq %rdi
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# ifndef USE_AS_STRCHRNUL
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/* Found CHAR or the null byte. */
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@@ -113,9 +106,10 @@ L(first_vec_x1):
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addq %rdi, %rax
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VZEROUPPER_RETURN
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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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- tzcntl %eax, %eax
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+ /* Use bsf to save code size. */
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+ bsfl %eax, %eax
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addq $(VEC_SIZE + 1), %rdi
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# ifndef USE_AS_STRCHRNUL
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/* Found CHAR or the null byte. */
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@@ -125,9 +119,10 @@ L(first_vec_x2):
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addq %rdi, %rax
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VZEROUPPER_RETURN
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- .p2align 4
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+ .p2align 4,, 8
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L(first_vec_x3):
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- tzcntl %eax, %eax
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+ /* Use bsf to save code size. */
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+ bsfl %eax, %eax
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addq $(VEC_SIZE * 2 + 1), %rdi
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# ifndef USE_AS_STRCHRNUL
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/* Found CHAR or the null byte. */
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@@ -137,6 +132,21 @@ L(first_vec_x3):
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addq %rdi, %rax
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VZEROUPPER_RETURN
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+ .p2align 4,, 10
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+L(first_vec_x4):
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+ /* Use bsf to save code size. */
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+ bsfl %eax, %eax
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+ addq $(VEC_SIZE * 3 + 1), %rdi
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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_REG
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+ jne L(zero)
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+# endif
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+ addq %rdi, %rax
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+ VZEROUPPER_RETURN
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+
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+
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+
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.p2align 4
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L(aligned_more):
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/* Align data to VEC_SIZE - 1. This is the same number of
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@@ -146,90 +156,92 @@ L(aligned_more):
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L(cross_page_continue):
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/* Check the next 4 * VEC_SIZE. Only one VEC_SIZE at a time
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since data is only aligned to VEC_SIZE. */
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- vmovdqa 1(%rdi), %ymm8
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- VPCMPEQ %ymm8, %ymm0, %ymm1
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- VPCMPEQ %ymm8, %ymm9, %ymm2
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- vpor %ymm1, %ymm2, %ymm1
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- vpmovmskb %ymm1, %eax
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+ vmovdqa 1(%rdi), %ymm2
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+ VPCMPEQ %ymm2, %ymm0, %ymm3
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+ VPCMPEQ %ymm2, %ymm1, %ymm2
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+ vpor %ymm3, %ymm2, %ymm3
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+ vpmovmskb %ymm3, %eax
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testl %eax, %eax
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jnz L(first_vec_x1)
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- vmovdqa (VEC_SIZE + 1)(%rdi), %ymm8
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- VPCMPEQ %ymm8, %ymm0, %ymm1
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- VPCMPEQ %ymm8, %ymm9, %ymm2
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- vpor %ymm1, %ymm2, %ymm1
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- vpmovmskb %ymm1, %eax
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+ vmovdqa (VEC_SIZE + 1)(%rdi), %ymm2
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+ VPCMPEQ %ymm2, %ymm0, %ymm3
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+ VPCMPEQ %ymm2, %ymm1, %ymm2
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+ vpor %ymm3, %ymm2, %ymm3
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+ vpmovmskb %ymm3, %eax
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testl %eax, %eax
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jnz L(first_vec_x2)
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- vmovdqa (VEC_SIZE * 2 + 1)(%rdi), %ymm8
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- VPCMPEQ %ymm8, %ymm0, %ymm1
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- VPCMPEQ %ymm8, %ymm9, %ymm2
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- vpor %ymm1, %ymm2, %ymm1
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- vpmovmskb %ymm1, %eax
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+ vmovdqa (VEC_SIZE * 2 + 1)(%rdi), %ymm2
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+ VPCMPEQ %ymm2, %ymm0, %ymm3
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+ VPCMPEQ %ymm2, %ymm1, %ymm2
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+ vpor %ymm3, %ymm2, %ymm3
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+ vpmovmskb %ymm3, %eax
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testl %eax, %eax
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jnz L(first_vec_x3)
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- vmovdqa (VEC_SIZE * 3 + 1)(%rdi), %ymm8
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- VPCMPEQ %ymm8, %ymm0, %ymm1
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- VPCMPEQ %ymm8, %ymm9, %ymm2
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- vpor %ymm1, %ymm2, %ymm1
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- vpmovmskb %ymm1, %eax
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+ vmovdqa (VEC_SIZE * 3 + 1)(%rdi), %ymm2
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+ VPCMPEQ %ymm2, %ymm0, %ymm3
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+ VPCMPEQ %ymm2, %ymm1, %ymm2
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+ vpor %ymm3, %ymm2, %ymm3
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+ vpmovmskb %ymm3, %eax
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testl %eax, %eax
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jnz L(first_vec_x4)
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- /* Align data to VEC_SIZE * 4 - 1. */
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- addq $(VEC_SIZE * 4 + 1), %rdi
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- andq $-(VEC_SIZE * 4), %rdi
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+ /* Align data to VEC_SIZE * 4 - 1. */
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+ incq %rdi
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+ orq $(VEC_SIZE * 4 - 1), %rdi
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.p2align 4
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L(loop_4x_vec):
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/* Compare 4 * VEC at a time forward. */
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- vmovdqa (%rdi), %ymm5
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- vmovdqa (VEC_SIZE)(%rdi), %ymm6
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- vmovdqa (VEC_SIZE * 2)(%rdi), %ymm7
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- vmovdqa (VEC_SIZE * 3)(%rdi), %ymm8
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+ vmovdqa 1(%rdi), %ymm6
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+ vmovdqa (VEC_SIZE + 1)(%rdi), %ymm7
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/* Leaves only CHARS matching esi as 0. */
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- vpxor %ymm5, %ymm0, %ymm1
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vpxor %ymm6, %ymm0, %ymm2
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vpxor %ymm7, %ymm0, %ymm3
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- vpxor %ymm8, %ymm0, %ymm4
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- VPMINU %ymm1, %ymm5, %ymm1
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VPMINU %ymm2, %ymm6, %ymm2
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VPMINU %ymm3, %ymm7, %ymm3
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- VPMINU %ymm4, %ymm8, %ymm4
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- VPMINU %ymm1, %ymm2, %ymm5
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- VPMINU %ymm3, %ymm4, %ymm6
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+ vmovdqa (VEC_SIZE * 2 + 1)(%rdi), %ymm6
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+ vmovdqa (VEC_SIZE * 3 + 1)(%rdi), %ymm7
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+
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+ vpxor %ymm6, %ymm0, %ymm4
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+ vpxor %ymm7, %ymm0, %ymm5
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+
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+ VPMINU %ymm4, %ymm6, %ymm4
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+ VPMINU %ymm5, %ymm7, %ymm5
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- VPMINU %ymm5, %ymm6, %ymm6
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+ VPMINU %ymm2, %ymm3, %ymm6
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+ VPMINU %ymm4, %ymm5, %ymm7
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- VPCMPEQ %ymm6, %ymm9, %ymm6
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- vpmovmskb %ymm6, %ecx
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+ VPMINU %ymm6, %ymm7, %ymm7
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+
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+ VPCMPEQ %ymm7, %ymm1, %ymm7
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+ vpmovmskb %ymm7, %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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-
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- VPCMPEQ %ymm1, %ymm9, %ymm1
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- vpmovmskb %ymm1, %eax
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+ VPCMPEQ %ymm2, %ymm1, %ymm2
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+ vpmovmskb %ymm2, %eax
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testl %eax, %eax
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jnz L(last_vec_x0)
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- VPCMPEQ %ymm5, %ymm9, %ymm2
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- vpmovmskb %ymm2, %eax
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+ VPCMPEQ %ymm3, %ymm1, %ymm3
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+ vpmovmskb %ymm3, %eax
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testl %eax, %eax
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jnz L(last_vec_x1)
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- VPCMPEQ %ymm3, %ymm9, %ymm3
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- vpmovmskb %ymm3, %eax
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+ VPCMPEQ %ymm4, %ymm1, %ymm4
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+ vpmovmskb %ymm4, %eax
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/* rcx has combined result from all 4 VEC. It will only be used
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if the first 3 other VEC all did not contain a match. */
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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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- subq $(VEC_SIZE * 2), %rdi
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+ subq $(VEC_SIZE * 2 - 1), %rdi
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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_REG
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@@ -239,10 +251,11 @@ L(loop_4x_vec):
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VZEROUPPER_RETURN
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- .p2align 4
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+ .p2align 4,, 10
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L(last_vec_x0):
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- tzcntl %eax, %eax
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- addq $-(VEC_SIZE * 4), %rdi
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+ /* Use bsf to save code size. */
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+ bsfl %eax, %eax
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+ addq $-(VEC_SIZE * 4 - 1), %rdi
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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_REG
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@@ -251,16 +264,11 @@ L(last_vec_x0):
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addq %rdi, %rax
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VZEROUPPER_RETURN
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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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- VZEROUPPER_RETURN
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-# endif
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- .p2align 4
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+ .p2align 4,, 10
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L(last_vec_x1):
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tzcntl %eax, %eax
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- subq $(VEC_SIZE * 3), %rdi
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+ subq $(VEC_SIZE * 3 - 1), %rdi
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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_REG
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@@ -269,18 +277,23 @@ L(last_vec_x1):
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addq %rdi, %rax
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VZEROUPPER_RETURN
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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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+ VZEROUPPER_RETURN
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+# endif
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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 to VEC_SIZE - 1. */
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orq $(VEC_SIZE - 1), %rdi
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- vmovdqa -(VEC_SIZE - 1)(%rdi), %ymm8
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- VPCMPEQ %ymm8, %ymm0, %ymm1
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- VPCMPEQ %ymm8, %ymm9, %ymm2
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- vpor %ymm1, %ymm2, %ymm1
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- vpmovmskb %ymm1, %eax
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+ vmovdqa -(VEC_SIZE - 1)(%rdi), %ymm2
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+ VPCMPEQ %ymm2, %ymm0, %ymm3
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+ VPCMPEQ %ymm2, %ymm1, %ymm2
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+ vpor %ymm3, %ymm2, %ymm3
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+ vpmovmskb %ymm3, %eax
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/* Remove the leading bytes. sarxl only uses bits [5:0] of COUNT
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so no need to manually mod edx. */
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sarxl %edx, %eax, %eax
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@@ -291,13 +304,10 @@ L(cross_page_boundary):
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xorl %ecx, %ecx
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/* Found CHAR or the null byte. */
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cmp (%rdx, %rax), %CHAR_REG
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- leaq (%rdx, %rax), %rax
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- cmovne %rcx, %rax
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-# else
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- addq %rdx, %rax
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+ jne L(zero_end)
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# endif
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-L(return_vzeroupper):
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- ZERO_UPPER_VEC_REGISTERS_RETURN
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+ addq %rdx, %rax
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+ VZEROUPPER_RETURN
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END (STRCHR)
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-# endif
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+#endif
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--
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GitLab
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