1/* Optimized version of the standard bzero() function.
2 This file is part of the GNU C Library.
3 Copyright (C) 2000-2022 Free Software Foundation, Inc.
4
5 The GNU C Library is free software; you can redistribute it and/or
6 modify it under the terms of the GNU Lesser General Public
7 License as published by the Free Software Foundation; either
8 version 2.1 of the License, or (at your option) any later version.
9
10 The GNU C Library is distributed in the hope that it will be useful,
11 but WITHOUT ANY WARRANTY; without even the implied warranty of
12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
13 Lesser General Public License for more details.
14
15 You should have received a copy of the GNU Lesser General Public
16 License along with the GNU C Library; if not, see
17 <https://www.gnu.org/licenses/>. */
18
19/* Return: dest
20
21 Inputs:
22 in0: dest
23 in1: count
24
25 The algorithm is fairly straightforward: set byte by byte until we
26 we get to a 16B-aligned address, then loop on 128 B chunks using an
27 early store as prefetching, then loop on 32B chucks, then clear remaining
28 words, finally clear remaining bytes.
29 Since a stf.spill f0 can store 16B in one go, we use this instruction
30 to get peak speed. */
31
32#include <sysdep.h>
33#undef ret
34
35#define dest in0
36#define cnt in1
37
38#define tmp r31
39#define save_lc r30
40#define ptr0 r29
41#define ptr1 r28
42#define ptr2 r27
43#define ptr3 r26
44#define ptr9 r24
45#define loopcnt r23
46#define linecnt r22
47#define bytecnt r21
48
49// This routine uses only scratch predicate registers (p6 - p15)
50#define p_scr p6 // default register for same-cycle branches
51#define p_unalgn p9
52#define p_y p11
53#define p_n p12
54#define p_yy p13
55#define p_nn p14
56
57#define movi0 mov
58
59#define MIN1 15
60#define MIN1P1HALF 8
61#define LINE_SIZE 128
62#define LSIZE_SH 7 // shift amount
63#define PREF_AHEAD 8
64
65#define USE_FLP
66#if defined(USE_INT)
67#define store st8
68#define myval r0
69#elif defined(USE_FLP)
70#define store stf8
71#define myval f0
72#endif
73
74.align 64
75ENTRY(bzero)
76{ .mmi
77 .prologue
78 alloc tmp = ar.pfs, 2, 0, 0, 0
79 lfetch.nt1 [dest]
80 .save ar.lc, save_lc
81 movi0 save_lc = ar.lc
82} { .mmi
83 .body
84 mov ret0 = dest // return value
85 nop.m 0
86 cmp.eq p_scr, p0 = cnt, r0
87;; }
88{ .mmi
89 and ptr2 = -(MIN1+1), dest // aligned address
90 and tmp = MIN1, dest // prepare to check for alignment
91 tbit.nz p_y, p_n = dest, 0 // Do we have an odd address? (M_B_U)
92} { .mib
93 mov ptr1 = dest
94 nop.i 0
95(p_scr) br.ret.dpnt.many rp // return immediately if count = 0
96;; }
97{ .mib
98 cmp.ne p_unalgn, p0 = tmp, r0
99} { .mib // NB: # of bytes to move is 1
100 sub bytecnt = (MIN1+1), tmp // higher than loopcnt
101 cmp.gt p_scr, p0 = 16, cnt // is it a minimalistic task?
102(p_scr) br.cond.dptk.many .move_bytes_unaligned // go move just a few (M_B_U)
103;; }
104{ .mmi
105(p_unalgn) add ptr1 = (MIN1+1), ptr2 // after alignment
106(p_unalgn) add ptr2 = MIN1P1HALF, ptr2 // after alignment
107(p_unalgn) tbit.nz.unc p_y, p_n = bytecnt, 3 // should we do a st8 ?
108;; }
109{ .mib
110(p_y) add cnt = -8, cnt
111(p_unalgn) tbit.nz.unc p_yy, p_nn = bytecnt, 2 // should we do a st4 ?
112} { .mib
113(p_y) st8 [ptr2] = r0,-4
114(p_n) add ptr2 = 4, ptr2
115;; }
116{ .mib
117(p_yy) add cnt = -4, cnt
118(p_unalgn) tbit.nz.unc p_y, p_n = bytecnt, 1 // should we do a st2 ?
119} { .mib
120(p_yy) st4 [ptr2] = r0,-2
121(p_nn) add ptr2 = 2, ptr2
122;; }
123{ .mmi
124 mov tmp = LINE_SIZE+1 // for compare
125(p_y) add cnt = -2, cnt
126(p_unalgn) tbit.nz.unc p_yy, p_nn = bytecnt, 0 // should we do a st1 ?
127} { .mmi
128 nop.m 0
129(p_y) st2 [ptr2] = r0,-1
130(p_n) add ptr2 = 1, ptr2
131;; }
132
133{ .mmi
134(p_yy) st1 [ptr2] = r0
135 cmp.gt p_scr, p0 = tmp, cnt // is it a minimalistic task?
136} { .mbb
137(p_yy) add cnt = -1, cnt
138(p_scr) br.cond.dpnt.many .fraction_of_line // go move just a few
139;; }
140{ .mib
141 nop.m 0
142 shr.u linecnt = cnt, LSIZE_SH
143 nop.b 0
144;; }
145
146 .align 32
147.l1b: // ------------------// L1B: store ahead into cache lines; fill later
148{ .mmi
149 and tmp = -(LINE_SIZE), cnt // compute end of range
150 mov ptr9 = ptr1 // used for prefetching
151 and cnt = (LINE_SIZE-1), cnt // remainder
152} { .mmi
153 mov loopcnt = PREF_AHEAD-1 // default prefetch loop
154 cmp.gt p_scr, p0 = PREF_AHEAD, linecnt // check against actual value
155;; }
156{ .mmi
157(p_scr) add loopcnt = -1, linecnt
158 add ptr2 = 16, ptr1 // start of stores (beyond prefetch stores)
159 add ptr1 = tmp, ptr1 // first address beyond total range
160;; }
161{ .mmi
162 add tmp = -1, linecnt // next loop count
163 movi0 ar.lc = loopcnt
164;; }
165.pref_l1b:
166{ .mib
167 stf.spill [ptr9] = f0, 128 // Do stores one cache line apart
168 nop.i 0
169 br.cloop.dptk.few .pref_l1b
170;; }
171{ .mmi
172 add ptr0 = 16, ptr2 // Two stores in parallel
173 movi0 ar.lc = tmp
174;; }
175.l1bx:
176 { .mmi
177 stf.spill [ptr2] = f0, 32
178 stf.spill [ptr0] = f0, 32
179 ;; }
180 { .mmi
181 stf.spill [ptr2] = f0, 32
182 stf.spill [ptr0] = f0, 32
183 ;; }
184 { .mmi
185 stf.spill [ptr2] = f0, 32
186 stf.spill [ptr0] = f0, 64
187 cmp.lt p_scr, p0 = ptr9, ptr1 // do we need more prefetching?
188 ;; }
189{ .mmb
190 stf.spill [ptr2] = f0, 32
191(p_scr) stf.spill [ptr9] = f0, 128
192 br.cloop.dptk.few .l1bx
193;; }
194{ .mib
195 cmp.gt p_scr, p0 = 8, cnt // just a few bytes left ?
196(p_scr) br.cond.dpnt.many .move_bytes_from_alignment
197;; }
198
199.fraction_of_line:
200{ .mib
201 add ptr2 = 16, ptr1
202 shr.u loopcnt = cnt, 5 // loopcnt = cnt / 32
203;; }
204{ .mib
205 cmp.eq p_scr, p0 = loopcnt, r0
206 add loopcnt = -1, loopcnt
207(p_scr) br.cond.dpnt.many .store_words
208;; }
209{ .mib
210 and cnt = 0x1f, cnt // compute the remaining cnt
211 movi0 ar.lc = loopcnt
212;; }
213 .align 32
214.l2: // -----------------------------// L2A: store 32B in 2 cycles
215{ .mmb
216 store [ptr1] = myval, 8
217 store [ptr2] = myval, 8
218;; } { .mmb
219 store [ptr1] = myval, 24
220 store [ptr2] = myval, 24
221 br.cloop.dptk.many .l2
222;; }
223.store_words:
224{ .mib
225 cmp.gt p_scr, p0 = 8, cnt // just a few bytes left ?
226(p_scr) br.cond.dpnt.many .move_bytes_from_alignment // Branch
227;; }
228
229{ .mmi
230 store [ptr1] = myval, 8 // store
231 cmp.le p_y, p_n = 16, cnt //
232 add cnt = -8, cnt // subtract
233;; }
234{ .mmi
235(p_y) store [ptr1] = myval, 8 // store
236(p_y) cmp.le.unc p_yy, p_nn = 16, cnt
237(p_y) add cnt = -8, cnt // subtract
238;; }
239{ .mmi // store
240(p_yy) store [ptr1] = myval, 8
241(p_yy) add cnt = -8, cnt // subtract
242;; }
243
244.move_bytes_from_alignment:
245{ .mib
246 cmp.eq p_scr, p0 = cnt, r0
247 tbit.nz.unc p_y, p0 = cnt, 2 // should we terminate with a st4 ?
248(p_scr) br.cond.dpnt.few .restore_and_exit
249;; }
250{ .mib
251(p_y) st4 [ptr1] = r0,4
252 tbit.nz.unc p_yy, p0 = cnt, 1 // should we terminate with a st2 ?
253;; }
254{ .mib
255(p_yy) st2 [ptr1] = r0,2
256 tbit.nz.unc p_y, p0 = cnt, 0 // should we terminate with a st1 ?
257;; }
258
259{ .mib
260(p_y) st1 [ptr1] = r0
261;; }
262.restore_and_exit:
263{ .mib
264 nop.m 0
265 movi0 ar.lc = save_lc
266 br.ret.sptk.many rp
267;; }
268
269.move_bytes_unaligned:
270{ .mmi
271 .pred.rel "mutex",p_y, p_n
272 .pred.rel "mutex",p_yy, p_nn
273(p_n) cmp.le p_yy, p_nn = 4, cnt
274(p_y) cmp.le p_yy, p_nn = 5, cnt
275(p_n) add ptr2 = 2, ptr1
276} { .mmi
277(p_y) add ptr2 = 3, ptr1
278(p_y) st1 [ptr1] = r0, 1 // fill 1 (odd-aligned) byte
279(p_y) add cnt = -1, cnt // [15, 14 (or less) left]
280;; }
281{ .mmi
282(p_yy) cmp.le.unc p_y, p0 = 8, cnt
283 add ptr3 = ptr1, cnt // prepare last store
284 movi0 ar.lc = save_lc
285} { .mmi
286(p_yy) st2 [ptr1] = r0, 4 // fill 2 (aligned) bytes
287(p_yy) st2 [ptr2] = r0, 4 // fill 2 (aligned) bytes
288(p_yy) add cnt = -4, cnt // [11, 10 (o less) left]
289;; }
290{ .mmi
291(p_y) cmp.le.unc p_yy, p0 = 8, cnt
292 add ptr3 = -1, ptr3 // last store
293 tbit.nz p_scr, p0 = cnt, 1 // will there be a st2 at the end ?
294} { .mmi
295(p_y) st2 [ptr1] = r0, 4 // fill 2 (aligned) bytes
296(p_y) st2 [ptr2] = r0, 4 // fill 2 (aligned) bytes
297(p_y) add cnt = -4, cnt // [7, 6 (or less) left]
298;; }
299{ .mmi
300(p_yy) st2 [ptr1] = r0, 4 // fill 2 (aligned) bytes
301(p_yy) st2 [ptr2] = r0, 4 // fill 2 (aligned) bytes
302 // [3, 2 (or less) left]
303 tbit.nz p_y, p0 = cnt, 0 // will there be a st1 at the end ?
304} { .mmi
305(p_yy) add cnt = -4, cnt
306;; }
307{ .mmb
308(p_scr) st2 [ptr1] = r0 // fill 2 (aligned) bytes
309(p_y) st1 [ptr3] = r0 // fill last byte (using ptr3)
310 br.ret.sptk.many rp
311;; }
312END(bzero)
313

source code of glibc/sysdeps/ia64/bzero.S