Text file src/runtime/memmove_arm64.s

     1  // Copyright 2014 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  #include "textflag.h"
     6  
     7  // See memmove Go doc for important implementation constraints.
     8  
     9  // Register map
    10  //
    11  // dstin  R0
    12  // src    R1
    13  // count  R2
    14  // dst    R3 (same as R0, but gets modified in unaligned cases)
    15  // srcend R4
    16  // dstend R5
    17  // data   R6-R17
    18  // tmp1   R14
    19  
    20  // Copies are split into 3 main cases: small copies of up to 32 bytes, medium
    21  // copies of up to 128 bytes, and large copies. The overhead of the overlap
    22  // check is negligible since it is only required for large copies.
    23  //
    24  // Large copies use a software pipelined loop processing 64 bytes per iteration.
    25  // The destination pointer is 16-byte aligned to minimize unaligned accesses.
    26  // The loop tail is handled by always copying 64 bytes from the end.
    27  
    28  // func memmove(to, from unsafe.Pointer, n uintptr)
    29  TEXT runtime¬∑memmove<ABIInternal>(SB), NOSPLIT|NOFRAME, $0-24
    30  	CBZ	R2, copy0
    31  
    32  	// Small copies: 1..16 bytes
    33  	CMP	$16, R2
    34  	BLE	copy16
    35  
    36  	// Large copies
    37  	CMP	$128, R2
    38  	BHI	copy_long
    39  	CMP	$32, R2
    40  	BHI	copy32_128
    41  
    42  	// Small copies: 17..32 bytes.
    43  	LDP	(R1), (R6, R7)
    44  	ADD	R1, R2, R4          // R4 points just past the last source byte
    45  	LDP	-16(R4), (R12, R13)
    46  	STP	(R6, R7), (R0)
    47  	ADD	R0, R2, R5          // R5 points just past the last destination byte
    48  	STP	(R12, R13), -16(R5)
    49  	RET
    50  
    51  // Small copies: 1..16 bytes.
    52  copy16:
    53  	ADD	R1, R2, R4 // R4 points just past the last source byte
    54  	ADD	R0, R2, R5 // R5 points just past the last destination byte
    55  	CMP	$8, R2
    56  	BLT	copy7
    57  	MOVD	(R1), R6
    58  	MOVD	-8(R4), R7
    59  	MOVD	R6, (R0)
    60  	MOVD	R7, -8(R5)
    61  	RET
    62  
    63  copy7:
    64  	TBZ	$2, R2, copy3
    65  	MOVWU	(R1), R6
    66  	MOVWU	-4(R4), R7
    67  	MOVW	R6, (R0)
    68  	MOVW	R7, -4(R5)
    69  	RET
    70  
    71  copy3:
    72  	TBZ	$1, R2, copy1
    73  	MOVHU	(R1), R6
    74  	MOVHU	-2(R4), R7
    75  	MOVH	R6, (R0)
    76  	MOVH	R7, -2(R5)
    77  	RET
    78  
    79  copy1:
    80  	MOVBU	(R1), R6
    81  	MOVB	R6, (R0)
    82  
    83  copy0:
    84  	RET
    85  
    86  	// Medium copies: 33..128 bytes.
    87  copy32_128:
    88  	ADD	R1, R2, R4          // R4 points just past the last source byte
    89  	ADD	R0, R2, R5          // R5 points just past the last destination byte
    90  	LDP	(R1), (R6, R7)
    91  	LDP	16(R1), (R8, R9)
    92  	LDP	-32(R4), (R10, R11)
    93  	LDP	-16(R4), (R12, R13)
    94  	CMP	$64, R2
    95  	BHI	copy128
    96  	STP	(R6, R7), (R0)
    97  	STP	(R8, R9), 16(R0)
    98  	STP	(R10, R11), -32(R5)
    99  	STP	(R12, R13), -16(R5)
   100  	RET
   101  
   102  	// Copy 65..128 bytes.
   103  copy128:
   104  	LDP	32(R1), (R14, R15)
   105  	LDP	48(R1), (R16, R17)
   106  	CMP	$96, R2
   107  	BLS	copy96
   108  	LDP	-64(R4), (R2, R3)
   109  	LDP	-48(R4), (R1, R4)
   110  	STP	(R2, R3), -64(R5)
   111  	STP	(R1, R4), -48(R5)
   112  
   113  copy96:
   114  	STP	(R6, R7), (R0)
   115  	STP	(R8, R9), 16(R0)
   116  	STP	(R14, R15), 32(R0)
   117  	STP	(R16, R17), 48(R0)
   118  	STP	(R10, R11), -32(R5)
   119  	STP	(R12, R13), -16(R5)
   120  	RET
   121  
   122  	// Copy more than 128 bytes.
   123  copy_long:
   124  	ADD	R1, R2, R4 // R4 points just past the last source byte
   125  	ADD	R0, R2, R5 // R5 points just past the last destination byte
   126  	MOVD	ZR, R7
   127  	MOVD	ZR, R8
   128  
   129  	CMP	$1024, R2
   130  	BLT	backward_check
   131  	// feature detect to decide how to align
   132  	MOVBU	runtime¬∑arm64UseAlignedLoads(SB), R6
   133  	CBNZ	R6, use_aligned_loads
   134  	MOVD	R0, R7
   135  	MOVD	R5, R8
   136  	B	backward_check
   137  use_aligned_loads:
   138  	MOVD	R1, R7
   139  	MOVD	R4, R8
   140  	// R7 and R8 are used here for the realignment calculation. In
   141  	// the use_aligned_loads case, R7 is the src pointer and R8 is
   142  	// srcend pointer, which is used in the backward copy case.
   143  	// When doing aligned stores, R7 is the dst pointer and R8 is
   144  	// the dstend pointer.
   145  
   146  backward_check:
   147  	// Use backward copy if there is an overlap.
   148  	SUB	R1, R0, R14
   149  	CBZ	R14, copy0
   150  	CMP	R2, R14
   151  	BCC	copy_long_backward
   152  
   153  	// Copy 16 bytes and then align src (R1) or dst (R0) to 16-byte alignment.
   154  	LDP	(R1), (R12, R13)     // Load  A
   155  	AND	$15, R7, R14         // Calculate the realignment offset
   156  	SUB	R14, R1, R1
   157  	SUB	R14, R0, R3          // move dst back same amount as src
   158  	ADD	R14, R2, R2
   159  	LDP	16(R1), (R6, R7)     // Load   B
   160  	STP	(R12, R13), (R0)     // Store A
   161  	LDP	32(R1), (R8, R9)     // Load    C
   162  	LDP	48(R1), (R10, R11)   // Load     D
   163  	LDP.W	64(R1), (R12, R13)   // Load      E
   164  	// 80 bytes have been loaded; if less than 80+64 bytes remain, copy from the end
   165  	SUBS	$144, R2, R2
   166  	BLS	copy64_from_end
   167  
   168  loop64:
   169  	STP	(R6, R7), 16(R3)     // Store  B
   170  	LDP	16(R1), (R6, R7)     // Load   B (next iteration)
   171  	STP	(R8, R9), 32(R3)     // Store   C
   172  	LDP	32(R1), (R8, R9)     // Load    C
   173  	STP	(R10, R11), 48(R3)   // Store    D
   174  	LDP	48(R1), (R10, R11)   // Load     D
   175  	STP.W	(R12, R13), 64(R3)   // Store     E
   176  	LDP.W	64(R1), (R12, R13)   // Load      E
   177  	SUBS	$64, R2, R2
   178  	BHI	loop64
   179  
   180  	// Write the last iteration and copy 64 bytes from the end.
   181  copy64_from_end:
   182  	LDP	-64(R4), (R14, R15)  // Load       F
   183  	STP	(R6, R7), 16(R3)     // Store  B
   184  	LDP	-48(R4), (R6, R7)    // Load        G
   185  	STP	(R8, R9), 32(R3)     // Store   C
   186  	LDP	-32(R4), (R8, R9)    // Load         H
   187  	STP	(R10, R11), 48(R3)   // Store    D
   188  	LDP	-16(R4), (R10, R11)  // Load          I
   189  	STP	(R12, R13), 64(R3)   // Store     E
   190  	STP	(R14, R15), -64(R5)  // Store      F
   191  	STP	(R6, R7), -48(R5)    // Store       G
   192  	STP	(R8, R9), -32(R5)    // Store        H
   193  	STP	(R10, R11), -16(R5)  // Store         I
   194  	RET
   195  
   196  	// Large backward copy for overlapping copies.
   197  	// Copy 16 bytes and then align srcend (R4) or dstend (R5) to 16-byte alignment.
   198  copy_long_backward:
   199  	LDP	-16(R4), (R12, R13)
   200  	AND	$15, R8, R14
   201  	SUB	R14, R4, R4
   202  	SUB	R14, R2, R2
   203  	LDP	-16(R4), (R6, R7)
   204  	STP	(R12, R13), -16(R5)
   205  	LDP	-32(R4), (R8, R9)
   206  	LDP	-48(R4), (R10, R11)
   207  	LDP.W	-64(R4), (R12, R13)
   208  	SUB	R14, R5, R5
   209  	SUBS	$128, R2, R2
   210  	BLS	copy64_from_start
   211  
   212  loop64_backward:
   213  	STP	(R6, R7), -16(R5)
   214  	LDP	-16(R4), (R6, R7)
   215  	STP	(R8, R9), -32(R5)
   216  	LDP	-32(R4), (R8, R9)
   217  	STP	(R10, R11), -48(R5)
   218  	LDP	-48(R4), (R10, R11)
   219  	STP.W	(R12, R13), -64(R5)
   220  	LDP.W	-64(R4), (R12, R13)
   221  	SUBS	$64, R2, R2
   222  	BHI	loop64_backward
   223  
   224  	// Write the last iteration and copy 64 bytes from the start.
   225  copy64_from_start:
   226  	LDP	48(R1), (R2, R3)
   227  	STP	(R6, R7), -16(R5)
   228  	LDP	32(R1), (R6, R7)
   229  	STP	(R8, R9), -32(R5)
   230  	LDP	16(R1), (R8, R9)
   231  	STP	(R10, R11), -48(R5)
   232  	LDP	(R1), (R10, R11)
   233  	STP	(R12, R13), -64(R5)
   234  	STP	(R2, R3), 48(R0)
   235  	STP	(R6, R7), 32(R0)
   236  	STP	(R8, R9), 16(R0)
   237  	STP	(R10, R11), (R0)
   238  	RET
   239  

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