Line data Source code
1 : /* Platform-independent deterministic sort function.
2 : Copyright (C) 2018-2026 Free Software Foundation, Inc.
3 : Contributed by Alexander Monakov.
4 :
5 : This file is part of GCC.
6 :
7 : GCC is free software; you can redistribute it and/or modify it
8 : under the terms of the GNU General Public License as published by the
9 : Free Software Foundation; either version 3, or (at your option) any
10 : later version.
11 :
12 : GCC is distributed in the hope that it will be useful, but WITHOUT
13 : ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
14 : FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
15 : for more details.
16 :
17 : You should have received a copy of the GNU General Public License
18 : along with GCC; see the file COPYING3. If not see
19 : <http://www.gnu.org/licenses/>. */
20 :
21 : /* This implements a sort function suitable for GCC use cases:
22 : - signature-compatible to C qsort, but relaxed contract:
23 : - may apply the comparator to elements in a temporary buffer
24 : - may abort on allocation failure
25 : - deterministic (but not necessarily stable)
26 : - fast, especially for common cases (0-5 elements of size 8 or 4)
27 :
28 : The implementation uses sorting networks for up to 5 elements and
29 : a merge sort on top of that. Neither stage has branches depending on
30 : comparator result, trading extra arithmetic for branch mispredictions. */
31 :
32 : #ifdef GENERATOR_FILE
33 : #include "bconfig.h"
34 : #else
35 : #include "config.h"
36 : #endif
37 :
38 : #include "system.h"
39 :
40 : #ifdef __GNUC__
41 : #define noinline __attribute__ ((__noinline__))
42 : #else
43 : #define noinline
44 : #endif
45 :
46 : /* C-style qsort comparator function type. */
47 : typedef int cmp_fn (const void *, const void *);
48 :
49 : /* Structure holding read-mostly (read-only in netsort) context. */
50 : struct sort_ctx
51 : {
52 : cmp_fn *cmp; // pointer to comparator
53 : char *out; // output buffer
54 : size_t n; // number of elements
55 : size_t size; // element size
56 : size_t nlim; // limit for using sorting networks
57 : };
58 :
59 : /* Like sort_ctx, but for use with qsort_r-style comparators. Several
60 : functions in this file are templates that work with either context type. */
61 : struct sort_r_ctx
62 : {
63 : void *data;
64 : sort_r_cmp_fn *cmp_;
65 : char *out;
66 : size_t n;
67 : size_t size;
68 : size_t nlim;
69 63098630 : int cmp (const void *a, const void *b)
70 : {
71 19503966 : return cmp_ (a, b, data);
72 : }
73 : };
74 :
75 : /* Helper for netsort. Permute, possibly in-place, 2 or 3 elements,
76 : placing E0 to C->OUT, E1 to C->OUT + C->SIZE, and so on. */
77 : template<typename sort_ctx>
78 : static void
79 191025363 : reorder23 (sort_ctx *c, char *e0, char *e1, char *e2)
80 : {
81 : #define REORDER_23(TYPE, STRIDE, OFFSET) \
82 : do { \
83 : TYPE t0, t1; \
84 : memcpy (&t0, e0 + OFFSET, sizeof (TYPE)); \
85 : memcpy (&t1, e1 + OFFSET, sizeof (TYPE)); \
86 : char *out = c->out + OFFSET; \
87 : if (LIKELY (c->n == 3)) \
88 : memmove (out + 2*STRIDE, e2 + OFFSET, sizeof (TYPE));\
89 : memcpy (out, &t0, sizeof (TYPE)); out += STRIDE; \
90 : memcpy (out, &t1, sizeof (TYPE)); \
91 : } while (0)
92 :
93 191025363 : if (LIKELY (c->size == sizeof (size_t)))
94 172165569 : REORDER_23 (size_t, sizeof (size_t), 0);
95 18859794 : else if (LIKELY (c->size == sizeof (int)))
96 7243901 : REORDER_23 (int, sizeof (int), 0);
97 : else
98 : {
99 : size_t offset = 0, step = sizeof (size_t);
100 51676514 : for (; offset + step <= c->size; offset += step)
101 40060621 : REORDER_23 (size_t, c->size, offset);
102 12639469 : for (; offset < c->size; offset++)
103 1023576 : REORDER_23 (char, c->size, offset);
104 : }
105 191025363 : }
106 :
107 : /* Like reorder23, but permute 4 or 5 elements. */
108 : template<typename sort_ctx>
109 : static void
110 177211423 : reorder45 (sort_ctx *c, char *e0, char *e1, char *e2, char *e3, char *e4)
111 : {
112 : #define REORDER_45(TYPE, STRIDE, OFFSET) \
113 : do { \
114 : TYPE t0, t1, t2, t3; \
115 : memcpy (&t0, e0 + OFFSET, sizeof (TYPE)); \
116 : memcpy (&t1, e1 + OFFSET, sizeof (TYPE)); \
117 : memcpy (&t2, e2 + OFFSET, sizeof (TYPE)); \
118 : memcpy (&t3, e3 + OFFSET, sizeof (TYPE)); \
119 : char *out = c->out + OFFSET; \
120 : if (LIKELY (c->n == 5)) \
121 : memmove (out + 4*STRIDE, e4 + OFFSET, sizeof (TYPE));\
122 : memcpy (out, &t0, sizeof (TYPE)); out += STRIDE; \
123 : memcpy (out, &t1, sizeof (TYPE)); out += STRIDE; \
124 : memcpy (out, &t2, sizeof (TYPE)); out += STRIDE; \
125 : memcpy (out, &t3, sizeof (TYPE)); \
126 : } while (0)
127 :
128 177211423 : if (LIKELY (c->size == sizeof (size_t)))
129 163942698 : REORDER_45 (size_t, sizeof (size_t), 0);
130 13268725 : else if (LIKELY (c->size == sizeof (int)))
131 8661571 : REORDER_45 (int, sizeof (int), 0);
132 : else
133 : {
134 : size_t offset = 0, step = sizeof (size_t);
135 20335220 : for (; offset + step <= c->size; offset += step)
136 15728066 : REORDER_45 (size_t, c->size, offset);
137 5817758 : for (; offset < c->size; offset++)
138 1210604 : REORDER_45 (char, c->size, offset);
139 : }
140 177211423 : }
141 :
142 : /* Helper for netsort. Invoke comparator CMP on E0 and E1.
143 : Return E0^E1 if E0 compares less than E1, zero otherwise.
144 : This is noinline to avoid code growth and confine invocation
145 : to a single call site, assisting indirect branch prediction. */
146 : template<typename sort_ctx>
147 : noinline static intptr_t
148 1624384334 : cmp1 (char *e0, char *e1, sort_ctx *c)
149 : {
150 1624384334 : intptr_t x = (intptr_t)e0 ^ (intptr_t)e1;
151 1624384334 : return x & (c->cmp (e0, e1) >> 31);
152 : }
153 :
154 : /* Apply a sorting network to 2 to 5 elements from IN, placing them into C->OUT.
155 : IN may be equal to C->OUT, in which case elements are sorted in place. */
156 : template<typename sort_ctx>
157 : static void
158 368236786 : netsort (char *in, sort_ctx *c)
159 : {
160 : #define CMP(e0, e1) \
161 : do { \
162 : intptr_t x = cmp1 (e1, e0, c); \
163 : e0 = (char *)((intptr_t)e0 ^ x); \
164 : e1 = (char *)((intptr_t)e1 ^ x); \
165 : } while (0)
166 :
167 368236786 : char *e0 = in, *e1 = e0 + c->size, *e2 = e1 + c->size;
168 368236786 : CMP (e0, e1);
169 368236786 : if (LIKELY (c->n == 3))
170 : {
171 144611798 : CMP (e1, e2);
172 144611798 : CMP (e0, e1);
173 : }
174 368236786 : if (c->n <= 3)
175 191025363 : return reorder23 (c, e0, e1, e2);
176 177211423 : char *e3 = e2 + c->size, *e4 = e3 + c->size;
177 177211423 : if (LIKELY (c->n == 5))
178 : {
179 64519565 : CMP (e3, e4);
180 64519565 : CMP (e2, e4);
181 : }
182 177211423 : CMP (e2, e3);
183 177211423 : if (LIKELY (c->n == 5))
184 : {
185 64519565 : CMP (e0, e3);
186 64519565 : CMP (e1, e4);
187 : }
188 177211423 : CMP (e0, e2);
189 177211423 : CMP (e1, e3);
190 177211423 : CMP (e1, e2);
191 177211423 : reorder45 (c, e0, e1, e2, e3, e4);
192 : }
193 :
194 : /* Execute merge sort on N elements from IN, placing them into OUT,
195 : using TMP as temporary storage if IN is equal to OUT.
196 : This is a stable sort if netsort is used only for 2 or 3 elements. */
197 : template<typename sort_ctx>
198 : static void
199 563698636 : mergesort (char *in, sort_ctx *c, size_t n, char *out, char *tmp)
200 : {
201 563698636 : if (LIKELY (n <= c->nlim))
202 : {
203 368236786 : c->out = out;
204 368236786 : c->n = n;
205 368236786 : return netsort (in, c);
206 : }
207 195461850 : size_t nl = n / 2, nr = n - nl, sz = nl * c->size;
208 195461850 : char *mid = in + sz, *r = out + sz, *l = in == out ? tmp : in;
209 : /* Sort the right half, outputting to right half of OUT. */
210 195461850 : mergesort (mid, c, nr, r, tmp);
211 : /* Sort the left half, leaving left half of OUT free. */
212 195461850 : mergesort (in, c, nl, l, mid);
213 : /* Merge sorted halves given by L, R to [OUT, END). */
214 : #define MERGE_ELTSIZE(SIZE) \
215 : do { \
216 : intptr_t mr = c->cmp (r, l) >> 31; \
217 : intptr_t lr = (intptr_t)l ^ (intptr_t)r; \
218 : lr = (intptr_t)l ^ (lr & mr); \
219 : out = (char *)memcpy (out, (char *)lr, SIZE); \
220 : out += SIZE; \
221 : r += mr & SIZE; \
222 : if (r == out) return; \
223 : l += ~mr & SIZE; \
224 : } while (r != end)
225 :
226 195461850 : if (LIKELY (c->cmp (r, l + (r - out) - c->size) < 0))
227 : {
228 133009928 : char *end = out + n * c->size;
229 133009928 : if (sizeof (size_t) == 8 && LIKELY (c->size == 8))
230 2345528482 : MERGE_ELTSIZE (8);
231 9806077 : else if (LIKELY (c->size == 4))
232 127653958 : MERGE_ELTSIZE (4);
233 : else
234 69370803 : MERGE_ELTSIZE (c->size);
235 : }
236 123554625 : memcpy (out, l, r - out);
237 : }
238 :
239 : #if CHECKING_P
240 : /* Don't complain about cast from void* to function pointer. */
241 : #pragma GCC diagnostic push
242 : #pragma GCC diagnostic ignored "-Wconditionally-supported"
243 :
244 : /* Adapter for using two-argument comparators in functions expecting the
245 : three-argument sort_r_cmp_fn type. */
246 : static int
247 26243695765 : cmp2to3 (const void *a, const void *b, void *c)
248 : {
249 26243695765 : return ((cmp_fn *)c) (a, b);
250 : }
251 : #endif
252 :
253 : /* Replacement for C qsort. */
254 : void
255 194549767 : gcc_qsort (void *vbase, size_t n, size_t size, cmp_fn *cmp)
256 : {
257 194549767 : if (n < 2)
258 28756073 : return;
259 165793694 : size_t nlim = 5;
260 165793694 : bool stable = (ssize_t) size < 0;
261 165793694 : if (stable)
262 34763 : nlim = 3, size = ~size;
263 165793694 : char *base = (char *)vbase;
264 165793694 : sort_ctx c = {cmp, base, n, size, nlim};
265 165793694 : long long scratch[32];
266 165793694 : size_t bufsz = (n / 2) * size;
267 165793694 : void *buf = bufsz <= sizeof scratch ? scratch : xmalloc (bufsz);
268 165793694 : mergesort (base, &c, n, base, (char *)buf);
269 165793694 : if (buf != scratch)
270 1836775 : free (buf);
271 : #if CHECKING_P
272 165793694 : qsort_chk (vbase, n, size, cmp2to3, (void*)cmp);
273 165793694 : #pragma GCC diagnostic pop
274 : #endif
275 : }
276 :
277 : /* Substitute for Glibc qsort_r. */
278 : void
279 9826568 : gcc_sort_r (void *vbase, size_t n, size_t size, sort_r_cmp_fn *cmp, void *data)
280 : {
281 9826568 : if (n < 2)
282 2845326 : return;
283 6981242 : size_t nlim = 5;
284 6981242 : bool stable = (ssize_t) size < 0;
285 6981242 : if (stable)
286 6752 : nlim = 3, size = ~size;
287 6981242 : char *base = (char *)vbase;
288 6981242 : sort_r_ctx c = {data, cmp, base, n, size, nlim};
289 6981242 : long long scratch[32];
290 6981242 : size_t bufsz = (n / 2) * size;
291 6981242 : void *buf = bufsz <= sizeof scratch ? scratch : xmalloc (bufsz);
292 6981242 : mergesort (base, &c, n, base, (char *)buf);
293 6981242 : if (buf != scratch)
294 16384 : free (buf);
295 : #if CHECKING_P
296 6981242 : qsort_chk (vbase, n, size, cmp, data);
297 : #endif
298 : }
299 :
300 : /* Stable sort, signature-compatible to C qsort. */
301 : void
302 36877 : gcc_stablesort (void *vbase, size_t n, size_t size, cmp_fn *cmp)
303 : {
304 36877 : gcc_qsort (vbase, n, ~size, cmp);
305 36877 : }
306 :
307 : /* Stable sort, signature-compatible to Glibc qsort_r. */
308 : void
309 6752 : gcc_stablesort_r (void *vbase, size_t n, size_t size, sort_r_cmp_fn *cmp,
310 : void *data)
311 : {
312 6752 : gcc_sort_r (vbase, n, ~size, cmp, data);
313 6752 : }
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