1 | /* |
2 | * Simple C functions to supplement the C library |
3 | * |
4 | * Copyright (c) 2006 Fabrice Bellard |
5 | * |
6 | * Permission is hereby granted, free of charge, to any person obtaining a copy |
7 | * of this software and associated documentation files (the "Software"), to deal |
8 | * in the Software without restriction, including without limitation the rights |
9 | * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell |
10 | * copies of the Software, and to permit persons to whom the Software is |
11 | * furnished to do so, subject to the following conditions: |
12 | * |
13 | * The above copyright notice and this permission notice shall be included in |
14 | * all copies or substantial portions of the Software. |
15 | * |
16 | * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR |
17 | * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, |
18 | * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL |
19 | * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER |
20 | * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, |
21 | * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN |
22 | * THE SOFTWARE. |
23 | */ |
24 | #include "qemu/osdep.h" |
25 | #include "qemu/cutils.h" |
26 | #include "qemu/bswap.h" |
27 | |
28 | static bool |
29 | buffer_zero_int(const void *buf, size_t len) |
30 | { |
31 | if (unlikely(len < 8)) { |
32 | /* For a very small buffer, simply accumulate all the bytes. */ |
33 | const unsigned char *p = buf; |
34 | const unsigned char *e = buf + len; |
35 | unsigned char t = 0; |
36 | |
37 | do { |
38 | t |= *p++; |
39 | } while (p < e); |
40 | |
41 | return t == 0; |
42 | } else { |
43 | /* Otherwise, use the unaligned memory access functions to |
44 | handle the beginning and end of the buffer, with a couple |
45 | of loops handling the middle aligned section. */ |
46 | uint64_t t = ldq_he_p(buf); |
47 | const uint64_t *p = (uint64_t *)(((uintptr_t)buf + 8) & -8); |
48 | const uint64_t *e = (uint64_t *)(((uintptr_t)buf + len) & -8); |
49 | |
50 | for (; p + 8 <= e; p += 8) { |
51 | __builtin_prefetch(p + 8); |
52 | if (t) { |
53 | return false; |
54 | } |
55 | t = p[0] | p[1] | p[2] | p[3] | p[4] | p[5] | p[6] | p[7]; |
56 | } |
57 | while (p < e) { |
58 | t |= *p++; |
59 | } |
60 | t |= ldq_he_p(buf + len - 8); |
61 | |
62 | return t == 0; |
63 | } |
64 | } |
65 | |
66 | #if defined(CONFIG_AVX2_OPT) || defined(__SSE2__) |
67 | /* Do not use push_options pragmas unnecessarily, because clang |
68 | * does not support them. |
69 | */ |
70 | #ifdef CONFIG_AVX2_OPT |
71 | #pragma GCC push_options |
72 | #pragma GCC target("sse2") |
73 | #endif |
74 | #include <emmintrin.h> |
75 | |
76 | /* Note that each of these vectorized functions require len >= 64. */ |
77 | |
78 | static bool |
79 | buffer_zero_sse2(const void *buf, size_t len) |
80 | { |
81 | __m128i t = _mm_loadu_si128(buf); |
82 | __m128i *p = (__m128i *)(((uintptr_t)buf + 5 * 16) & -16); |
83 | __m128i *e = (__m128i *)(((uintptr_t)buf + len) & -16); |
84 | __m128i zero = _mm_setzero_si128(); |
85 | |
86 | /* Loop over 16-byte aligned blocks of 64. */ |
87 | while (likely(p <= e)) { |
88 | __builtin_prefetch(p); |
89 | t = _mm_cmpeq_epi8(t, zero); |
90 | if (unlikely(_mm_movemask_epi8(t) != 0xFFFF)) { |
91 | return false; |
92 | } |
93 | t = p[-4] | p[-3] | p[-2] | p[-1]; |
94 | p += 4; |
95 | } |
96 | |
97 | /* Finish the aligned tail. */ |
98 | t |= e[-3]; |
99 | t |= e[-2]; |
100 | t |= e[-1]; |
101 | |
102 | /* Finish the unaligned tail. */ |
103 | t |= _mm_loadu_si128(buf + len - 16); |
104 | |
105 | return _mm_movemask_epi8(_mm_cmpeq_epi8(t, zero)) == 0xFFFF; |
106 | } |
107 | #ifdef CONFIG_AVX2_OPT |
108 | #pragma GCC pop_options |
109 | #endif |
110 | |
111 | #ifdef CONFIG_AVX2_OPT |
112 | /* Note that due to restrictions/bugs wrt __builtin functions in gcc <= 4.8, |
113 | * the includes have to be within the corresponding push_options region, and |
114 | * therefore the regions themselves have to be ordered with increasing ISA. |
115 | */ |
116 | #pragma GCC push_options |
117 | #pragma GCC target("sse4") |
118 | #include <smmintrin.h> |
119 | |
120 | static bool |
121 | buffer_zero_sse4(const void *buf, size_t len) |
122 | { |
123 | __m128i t = _mm_loadu_si128(buf); |
124 | __m128i *p = (__m128i *)(((uintptr_t)buf + 5 * 16) & -16); |
125 | __m128i *e = (__m128i *)(((uintptr_t)buf + len) & -16); |
126 | |
127 | /* Loop over 16-byte aligned blocks of 64. */ |
128 | while (likely(p <= e)) { |
129 | __builtin_prefetch(p); |
130 | if (unlikely(!_mm_testz_si128(t, t))) { |
131 | return false; |
132 | } |
133 | t = p[-4] | p[-3] | p[-2] | p[-1]; |
134 | p += 4; |
135 | } |
136 | |
137 | /* Finish the aligned tail. */ |
138 | t |= e[-3]; |
139 | t |= e[-2]; |
140 | t |= e[-1]; |
141 | |
142 | /* Finish the unaligned tail. */ |
143 | t |= _mm_loadu_si128(buf + len - 16); |
144 | |
145 | return _mm_testz_si128(t, t); |
146 | } |
147 | |
148 | #pragma GCC pop_options |
149 | #pragma GCC push_options |
150 | #pragma GCC target("avx2") |
151 | #include <immintrin.h> |
152 | |
153 | static bool |
154 | buffer_zero_avx2(const void *buf, size_t len) |
155 | { |
156 | /* Begin with an unaligned head of 32 bytes. */ |
157 | __m256i t = _mm256_loadu_si256(buf); |
158 | __m256i *p = (__m256i *)(((uintptr_t)buf + 5 * 32) & -32); |
159 | __m256i *e = (__m256i *)(((uintptr_t)buf + len) & -32); |
160 | |
161 | if (likely(p <= e)) { |
162 | /* Loop over 32-byte aligned blocks of 128. */ |
163 | do { |
164 | __builtin_prefetch(p); |
165 | if (unlikely(!_mm256_testz_si256(t, t))) { |
166 | return false; |
167 | } |
168 | t = p[-4] | p[-3] | p[-2] | p[-1]; |
169 | p += 4; |
170 | } while (p <= e); |
171 | } else { |
172 | t |= _mm256_loadu_si256(buf + 32); |
173 | if (len <= 128) { |
174 | goto last2; |
175 | } |
176 | } |
177 | |
178 | /* Finish the last block of 128 unaligned. */ |
179 | t |= _mm256_loadu_si256(buf + len - 4 * 32); |
180 | t |= _mm256_loadu_si256(buf + len - 3 * 32); |
181 | last2: |
182 | t |= _mm256_loadu_si256(buf + len - 2 * 32); |
183 | t |= _mm256_loadu_si256(buf + len - 1 * 32); |
184 | |
185 | return _mm256_testz_si256(t, t); |
186 | } |
187 | #pragma GCC pop_options |
188 | #endif /* CONFIG_AVX2_OPT */ |
189 | |
190 | /* Note that for test_buffer_is_zero_next_accel, the most preferred |
191 | * ISA must have the least significant bit. |
192 | */ |
193 | #define CACHE_AVX2 1 |
194 | #define CACHE_SSE4 2 |
195 | #define CACHE_SSE2 4 |
196 | |
197 | /* Make sure that these variables are appropriately initialized when |
198 | * SSE2 is enabled on the compiler command-line, but the compiler is |
199 | * too old to support CONFIG_AVX2_OPT. |
200 | */ |
201 | #ifdef CONFIG_AVX2_OPT |
202 | # define INIT_CACHE 0 |
203 | # define INIT_ACCEL buffer_zero_int |
204 | #else |
205 | # ifndef __SSE2__ |
206 | # error "ISA selection confusion" |
207 | # endif |
208 | # define INIT_CACHE CACHE_SSE2 |
209 | # define INIT_ACCEL buffer_zero_sse2 |
210 | #endif |
211 | |
212 | static unsigned cpuid_cache = INIT_CACHE; |
213 | static bool (*buffer_accel)(const void *, size_t) = INIT_ACCEL; |
214 | |
215 | static void init_accel(unsigned cache) |
216 | { |
217 | bool (*fn)(const void *, size_t) = buffer_zero_int; |
218 | if (cache & CACHE_SSE2) { |
219 | fn = buffer_zero_sse2; |
220 | } |
221 | #ifdef CONFIG_AVX2_OPT |
222 | if (cache & CACHE_SSE4) { |
223 | fn = buffer_zero_sse4; |
224 | } |
225 | if (cache & CACHE_AVX2) { |
226 | fn = buffer_zero_avx2; |
227 | } |
228 | #endif |
229 | buffer_accel = fn; |
230 | } |
231 | |
232 | #ifdef CONFIG_AVX2_OPT |
233 | #include "qemu/cpuid.h" |
234 | |
235 | static void __attribute__((constructor)) init_cpuid_cache(void) |
236 | { |
237 | int max = __get_cpuid_max(0, NULL); |
238 | int a, b, c, d; |
239 | unsigned cache = 0; |
240 | |
241 | if (max >= 1) { |
242 | __cpuid(1, a, b, c, d); |
243 | if (d & bit_SSE2) { |
244 | cache |= CACHE_SSE2; |
245 | } |
246 | if (c & bit_SSE4_1) { |
247 | cache |= CACHE_SSE4; |
248 | } |
249 | |
250 | /* We must check that AVX is not just available, but usable. */ |
251 | if ((c & bit_OSXSAVE) && (c & bit_AVX) && max >= 7) { |
252 | int bv; |
253 | __asm("xgetbv" : "=a" (bv), "=d" (d) : "c" (0)); |
254 | __cpuid_count(7, 0, a, b, c, d); |
255 | if ((bv & 6) == 6 && (b & bit_AVX2)) { |
256 | cache |= CACHE_AVX2; |
257 | } |
258 | } |
259 | } |
260 | cpuid_cache = cache; |
261 | init_accel(cache); |
262 | } |
263 | #endif /* CONFIG_AVX2_OPT */ |
264 | |
265 | bool test_buffer_is_zero_next_accel(void) |
266 | { |
267 | /* If no bits set, we just tested buffer_zero_int, and there |
268 | are no more acceleration options to test. */ |
269 | if (cpuid_cache == 0) { |
270 | return false; |
271 | } |
272 | /* Disable the accelerator we used before and select a new one. */ |
273 | cpuid_cache &= cpuid_cache - 1; |
274 | init_accel(cpuid_cache); |
275 | return true; |
276 | } |
277 | |
278 | static bool select_accel_fn(const void *buf, size_t len) |
279 | { |
280 | if (likely(len >= 64)) { |
281 | return buffer_accel(buf, len); |
282 | } |
283 | return buffer_zero_int(buf, len); |
284 | } |
285 | |
286 | #else |
287 | #define select_accel_fn buffer_zero_int |
288 | bool test_buffer_is_zero_next_accel(void) |
289 | { |
290 | return false; |
291 | } |
292 | #endif |
293 | |
294 | /* |
295 | * Checks if a buffer is all zeroes |
296 | */ |
297 | bool buffer_is_zero(const void *buf, size_t len) |
298 | { |
299 | if (unlikely(len == 0)) { |
300 | return true; |
301 | } |
302 | |
303 | /* Fetch the beginning of the buffer while we select the accelerator. */ |
304 | __builtin_prefetch(buf); |
305 | |
306 | /* Use an optimized zero check if possible. Note that this also |
307 | includes a check for an unrolled loop over 64-bit integers. */ |
308 | return select_accel_fn(buf, len); |
309 | } |
310 | |