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Not only is this an obvious optimization: benchmark old MB/s new MB/s speedup BenchmarkMemmove1-4 35.35 29.65 0.84x BenchmarkMemmove2-4 63.78 52.53 0.82x BenchmarkMemmove3-4 89.72 73.96 0.82x BenchmarkMemmove4-4 109.94 95.73 0.87x BenchmarkMemmove5-4 127.60 112.80 0.88x BenchmarkMemmove6-4 143.59 126.67 0.88x BenchmarkMemmove7-4 157.90 138.92 0.88x BenchmarkMemmove8-4 167.18 231.81 1.39x BenchmarkMemmove9-4 175.23 252.07 1.44x BenchmarkMemmove10-4 165.68 261.10 1.58x BenchmarkMemmove11-4 174.43 263.31 1.51x BenchmarkMemmove12-4 180.76 267.56 1.48x BenchmarkMemmove13-4 189.06 284.93 1.51x BenchmarkMemmove14-4 186.31 284.72 1.53x BenchmarkMemmove15-4 195.75 281.62 1.44x BenchmarkMemmove16-4 202.96 439.23 2.16x BenchmarkMemmove32-4 264.77 775.77 2.93x BenchmarkMemmove64-4 306.81 1209.64 3.94x BenchmarkMemmove128-4 357.03 1515.41 4.24x BenchmarkMemmove256-4 380.77 2066.01 5.43x BenchmarkMemmove512-4 385.05 2556.45 6.64x BenchmarkMemmove1024-4 381.23 2804.10 7.36x BenchmarkMemmove2048-4 379.06 2814.83 7.43x BenchmarkMemmove4096-4 387.43 3064.96 7.91x BenchmarkMemmoveUnaligned1-4 28.91 25.40 0.88x BenchmarkMemmoveUnaligned2-4 56.13 47.56 0.85x BenchmarkMemmoveUnaligned3-4 74.32 69.31 0.93x BenchmarkMemmoveUnaligned4-4 97.02 83.58 0.86x BenchmarkMemmoveUnaligned5-4 110.17 103.62 0.94x BenchmarkMemmoveUnaligned6-4 124.95 113.26 0.91x BenchmarkMemmoveUnaligned7-4 142.37 130.82 0.92x BenchmarkMemmoveUnaligned8-4 151.20 205.64 1.36x BenchmarkMemmoveUnaligned9-4 166.97 215.42 1.29x BenchmarkMemmoveUnaligned10-4 148.49 221.22 1.49x BenchmarkMemmoveUnaligned11-4 159.47 239.57 1.50x BenchmarkMemmoveUnaligned12-4 163.52 247.32 1.51x BenchmarkMemmoveUnaligned13-4 167.55 256.54 1.53x BenchmarkMemmoveUnaligned14-4 175.12 251.03 1.43x BenchmarkMemmoveUnaligned15-4 192.10 267.13 1.39x BenchmarkMemmoveUnaligned16-4 190.76 378.87 1.99x BenchmarkMemmoveUnaligned32-4 259.02 562.98 2.17x BenchmarkMemmoveUnaligned64-4 317.72 842.44 2.65x BenchmarkMemmoveUnaligned128-4 355.43 1274.49 3.59x BenchmarkMemmoveUnaligned256-4 378.17 1815.74 4.80x BenchmarkMemmoveUnaligned512-4 362.15 2180.81 6.02x BenchmarkMemmoveUnaligned1024-4 376.07 2453.58 6.52x BenchmarkMemmoveUnaligned2048-4 381.66 2568.32 6.73x BenchmarkMemmoveUnaligned4096-4 398.51 2669.36 6.70x BenchmarkMemclr5-4 113.83 107.93 0.95x BenchmarkMemclr16-4 223.84 389.63 1.74x BenchmarkMemclr64-4 421.99 1209.58 2.87x BenchmarkMemclr256-4 525.94 2411.58 4.59x BenchmarkMemclr4096-4 581.66 4372.20 7.52x BenchmarkMemclr65536-4 565.84 4747.48 8.39x BenchmarkGoMemclr5-4 194.63 160.31 0.82x BenchmarkGoMemclr16-4 295.30 630.07 2.13x BenchmarkGoMemclr64-4 480.24 1884.03 3.92x BenchmarkGoMemclr256-4 540.23 2926.49 5.42x but it turns out that it's necessary to avoid the GC seeing partially written pointers. It's of course possible to be more sophisticated (using ldp/stp to move 16 bytes at a time in the core loop and unrolling the tail copying loops being the obvious ideas) but I wanted something simple and (reasonably) obviously correct. Fixes #12552 Change-Id: Iaeaf8a812cd06f4747ba2f792de1ded738890735 Reviewed-on: https://go-review.googlesource.com/14813 Reviewed-by: Austin Clements <austin@google.com>
38 lines
785 B
ArmAsm
38 lines
785 B
ArmAsm
// Copyright 2014 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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#include "textflag.h"
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// void runtime·memclr(void*, uintptr)
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TEXT runtime·memclr(SB),NOSPLIT,$0-16
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MOVD ptr+0(FP), R3
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MOVD n+8(FP), R4
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// TODO(mwhudson): this is written this way to avoid tickling
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// warnings from addpool when written as AND $7, R4, R6 (see
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// https://golang.org/issue/12708)
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AND $~7, R4, R5 // R5 is N&~7
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SUB R5, R4, R6 // R6 is N&7
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CMP $0, R5
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BEQ nowords
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ADD R3, R5, R5
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wordloop: // TODO: Optimize for unaligned ptr.
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MOVD.P $0, 8(R3)
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CMP R3, R5
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BNE wordloop
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nowords:
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CMP $0, R6
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BEQ done
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ADD R3, R6, R6
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byteloop:
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MOVBU.P $0, 1(R3)
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CMP R3, R6
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BNE byteloop
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done:
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RET
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