util/bufferiszero.c - third_party/qemu - Git at Google

 /*
  * Simple C functions to supplement the C library
  *
  * Copyright (c) 2006 Fabrice Bellard
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal
  * in the Software without restriction, including without limitation the rights
  * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
  * copies of the Software, and to permit persons to whom the Software is
  * furnished to do so, subject to the following conditions:
  *
  * The above copyright notice and this permission notice shall be included in
  * all copies or substantial portions of the Software.
  *
  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
  * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
  * THE SOFTWARE.
  */
 #include "qemu/osdep.h"
 #include "qemu/cutils.h"
 #include "qemu/bswap.h"
 #include "host/cpuinfo.h"

 static bool
 buffer_zero_int(const void *buf, size_t len)
 {
     if (unlikely(len < 8)) {
         /* For a very small buffer, simply accumulate all the bytes.  */
         const unsigned char *p = buf;
         const unsigned char *e = buf + len;
         unsigned char t = 0;

         do {
             t |= *p++;
         } while (p < e);

         return t == 0;
     } else {
         /* Otherwise, use the unaligned memory access functions to
            handle the beginning and end of the buffer, with a couple
            of loops handling the middle aligned section.  */
         uint64_t t = ldq_he_p(buf);
         const uint64_t *p = (uint64_t *)(((uintptr_t)buf + 8) & -8);
         const uint64_t *e = (uint64_t *)(((uintptr_t)buf + len) & -8);

         for (; p + 8 <= e; p += 8) {
             __builtin_prefetch(p + 8);
             if (t) {
                 return false;
             }
             t = p[0] | p[1] | p[2] | p[3] | p[4] | p[5] | p[6] | p[7];
         }
         while (p < e) {
             t |= *p++;
         }
         t |= ldq_he_p(buf + len - 8);

         return t == 0;
     }
 }

 #if defined(CONFIG_AVX512F_OPT) || defined(CONFIG_AVX2_OPT) || defined(__SSE2__)
 #include <immintrin.h>

 /* Note that each of these vectorized functions require len >= 64.  */

 static bool __attribute__((target("sse2")))
 buffer_zero_sse2(const void *buf, size_t len)
 {
     __m128i t = _mm_loadu_si128(buf);
     __m128i *p = (__m128i *)(((uintptr_t)buf + 5 * 16) & -16);
     __m128i *e = (__m128i *)(((uintptr_t)buf + len) & -16);
     __m128i zero = _mm_setzero_si128();

     /* Loop over 16-byte aligned blocks of 64.  */
     while (likely(p <= e)) {
         __builtin_prefetch(p);
         t = _mm_cmpeq_epi8(t, zero);
         if (unlikely(_mm_movemask_epi8(t) != 0xFFFF)) {
             return false;
         }
         t = p[-4] | p[-3] | p[-2] | p[-1];
         p += 4;
     }

     /* Finish the aligned tail.  */
     t |= e[-3];
     t |= e[-2];
     t |= e[-1];

     /* Finish the unaligned tail.  */
     t |= _mm_loadu_si128(buf + len - 16);

     return _mm_movemask_epi8(_mm_cmpeq_epi8(t, zero)) == 0xFFFF;
 }

 #ifdef CONFIG_AVX2_OPT
 static bool __attribute__((target("sse4")))
 buffer_zero_sse4(const void *buf, size_t len)
 {
     __m128i t = _mm_loadu_si128(buf);
     __m128i *p = (__m128i *)(((uintptr_t)buf + 5 * 16) & -16);
     __m128i *e = (__m128i *)(((uintptr_t)buf + len) & -16);

     /* Loop over 16-byte aligned blocks of 64.  */
     while (likely(p <= e)) {
         __builtin_prefetch(p);
         if (unlikely(!_mm_testz_si128(t, t))) {
             return false;
         }
         t = p[-4] | p[-3] | p[-2] | p[-1];
         p += 4;
     }

     /* Finish the aligned tail.  */
     t |= e[-3];
     t |= e[-2];
     t |= e[-1];

     /* Finish the unaligned tail.  */
     t |= _mm_loadu_si128(buf + len - 16);

     return _mm_testz_si128(t, t);
 }

 static bool __attribute__((target("avx2")))
 buffer_zero_avx2(const void *buf, size_t len)
 {
     /* Begin with an unaligned head of 32 bytes.  */
     __m256i t = _mm256_loadu_si256(buf);
     __m256i *p = (__m256i *)(((uintptr_t)buf + 5 * 32) & -32);
     __m256i *e = (__m256i *)(((uintptr_t)buf + len) & -32);

     /* Loop over 32-byte aligned blocks of 128.  */
     while (p <= e) {
         __builtin_prefetch(p);
         if (unlikely(!_mm256_testz_si256(t, t))) {
             return false;
         }
         t = p[-4] | p[-3] | p[-2] | p[-1];
         p += 4;
     } ;

     /* Finish the last block of 128 unaligned.  */
     t |= _mm256_loadu_si256(buf + len - 4 * 32);
     t |= _mm256_loadu_si256(buf + len - 3 * 32);
     t |= _mm256_loadu_si256(buf + len - 2 * 32);
     t |= _mm256_loadu_si256(buf + len - 1 * 32);

     return _mm256_testz_si256(t, t);
 }
 #endif /* CONFIG_AVX2_OPT */

 #ifdef CONFIG_AVX512F_OPT
 static bool __attribute__((target("avx512f")))
 buffer_zero_avx512(const void *buf, size_t len)
 {
     /* Begin with an unaligned head of 64 bytes.  */
     __m512i t = _mm512_loadu_si512(buf);
     __m512i *p = (__m512i *)(((uintptr_t)buf + 5 * 64) & -64);
     __m512i *e = (__m512i *)(((uintptr_t)buf + len) & -64);

     /* Loop over 64-byte aligned blocks of 256.  */
     while (p <= e) {
         __builtin_prefetch(p);
         if (unlikely(_mm512_test_epi64_mask(t, t))) {
             return false;
         }
         t = p[-4] | p[-3] | p[-2] | p[-1];
         p += 4;
     }

     t |= _mm512_loadu_si512(buf + len - 4 * 64);
     t |= _mm512_loadu_si512(buf + len - 3 * 64);
     t |= _mm512_loadu_si512(buf + len - 2 * 64);
     t |= _mm512_loadu_si512(buf + len - 1 * 64);

     return !_mm512_test_epi64_mask(t, t);

 }
 #endif /* CONFIG_AVX512F_OPT */

 /*
  * Make sure that these variables are appropriately initialized when
  * SSE2 is enabled on the compiler command-line, but the compiler is
  * too old to support CONFIG_AVX2_OPT.
  */
 #if defined(CONFIG_AVX512F_OPT) || defined(CONFIG_AVX2_OPT)
 # define INIT_USED     0
 # define INIT_LENGTH   0
 # define INIT_ACCEL    buffer_zero_int
 #else
 # ifndef __SSE2__
 #  error "ISA selection confusion"
 # endif
 # define INIT_USED     CPUINFO_SSE2
 # define INIT_LENGTH   64
 # define INIT_ACCEL    buffer_zero_sse2
 #endif

 static unsigned used_accel = INIT_USED;
 static unsigned length_to_accel = INIT_LENGTH;
 static bool (*buffer_accel)(const void *, size_t) = INIT_ACCEL;

 static unsigned __attribute__((noinline))
 select_accel_cpuinfo(unsigned info)
 {
     /* Array is sorted in order of algorithm preference. */
     static const struct {
         unsigned bit;
         unsigned len;
         bool (*fn)(const void *, size_t);
     } all[] = {
 #ifdef CONFIG_AVX512F_OPT
         { CPUINFO_AVX512F, 256, buffer_zero_avx512 },
 #endif
 #ifdef CONFIG_AVX2_OPT
         { CPUINFO_AVX2,    128, buffer_zero_avx2 },
         { CPUINFO_SSE4,     64, buffer_zero_sse4 },
 #endif
         { CPUINFO_SSE2,     64, buffer_zero_sse2 },
         { CPUINFO_ALWAYS,    0, buffer_zero_int },
     };

     for (unsigned i = 0; i < ARRAY_SIZE(all); ++i) {
         if (info & all[i].bit) {
             length_to_accel = all[i].len;
             buffer_accel = all[i].fn;
             return all[i].bit;
         }
     }
     return 0;
 }

 #if defined(CONFIG_AVX512F_OPT) || defined(CONFIG_AVX2_OPT)
 static void __attribute__((constructor)) init_accel(void)
 {
     used_accel = select_accel_cpuinfo(cpuinfo_init());
 }
 #endif /* CONFIG_AVX2_OPT */

 bool test_buffer_is_zero_next_accel(void)
 {
     /*
      * Accumulate the accelerators that we've already tested, and
      * remove them from the set to test this round.  We'll get back
      * a zero from select_accel_cpuinfo when there are no more.
      */
     unsigned used = select_accel_cpuinfo(cpuinfo & ~used_accel);
     used_accel |= used;
     return used;
 }

 static bool select_accel_fn(const void *buf, size_t len)
 {
     if (likely(len >= length_to_accel)) {
         return buffer_accel(buf, len);
     }
     return buffer_zero_int(buf, len);
 }

 #else
 #define select_accel_fn  buffer_zero_int
 bool test_buffer_is_zero_next_accel(void)
 {
     return false;
 }
 #endif

 /*
  * Checks if a buffer is all zeroes
  */
 bool buffer_is_zero(const void *buf, size_t len)
 {
     if (unlikely(len == 0)) {
         return true;
     }

     /* Fetch the beginning of the buffer while we select the accelerator.  */
     __builtin_prefetch(buf);

     /* Use an optimized zero check if possible.  Note that this also
        includes a check for an unrolled loop over 64-bit integers.  */
     return select_accel_fn(buf, len);
 }
	/*
	* Simple C functions to supplement the C library
	*
	* Copyright (c) 2006 Fabrice Bellard
	*
	* Permission is hereby granted, free of charge, to any person obtaining a copy
	* of this software and associated documentation files (the "Software"), to deal
	* in the Software without restriction, including without limitation the rights
	* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
	* copies of the Software, and to permit persons to whom the Software is
	* furnished to do so, subject to the following conditions:
	*
	* The above copyright notice and this permission notice shall be included in
	* all copies or substantial portions of the Software.
	*
	* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
	* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
	* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
	* THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
	* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
	* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
	* THE SOFTWARE.
	*/
	#include "qemu/osdep.h"
	#include "qemu/cutils.h"
	#include "qemu/bswap.h"
	#include "host/cpuinfo.h"

	static bool
	buffer_zero_int(const void *buf, size_t len)
	{
	if (unlikely(len < 8)) {
	/* For a very small buffer, simply accumulate all the bytes. */
	const unsigned char *p = buf;
	const unsigned char *e = buf + len;
	unsigned char t = 0;

	do {
	t \|= *p++;
	} while (p < e);

	return t == 0;
	} else {
	/* Otherwise, use the unaligned memory access functions to
	handle the beginning and end of the buffer, with a couple
	of loops handling the middle aligned section. */
	uint64_t t = ldq_he_p(buf);
	const uint64_t p = (uint64_t )(((uintptr_t)buf + 8) & -8);
	const uint64_t e = (uint64_t )(((uintptr_t)buf + len) & -8);

	for (; p + 8 <= e; p += 8) {
	__builtin_prefetch(p + 8);
	if (t) {
	return false;
	}
	t = p[0] \| p[1] \| p[2] \| p[3] \| p[4] \| p[5] \| p[6] \| p[7];
	}
	while (p < e) {
	t \|= *p++;
	}
	t \|= ldq_he_p(buf + len - 8);

	return t == 0;
	}
	}

	#if defined(CONFIG_AVX512F_OPT) \|\| defined(CONFIG_AVX2_OPT) \|\| defined(__SSE2__)
	#include <immintrin.h>

	/* Note that each of these vectorized functions require len >= 64. */

	static bool __attribute__((target("sse2")))
	buffer_zero_sse2(const void *buf, size_t len)
	{
	__m128i t = _mm_loadu_si128(buf);
	__m128i p = (__m128i )(((uintptr_t)buf + 5 * 16) & -16);
	__m128i e = (__m128i )(((uintptr_t)buf + len) & -16);
	__m128i zero = _mm_setzero_si128();

	/* Loop over 16-byte aligned blocks of 64. */
	while (likely(p <= e)) {
	__builtin_prefetch(p);
	t = _mm_cmpeq_epi8(t, zero);
	if (unlikely(_mm_movemask_epi8(t) != 0xFFFF)) {
	return false;
	}
	t = p[-4] \| p[-3] \| p[-2] \| p[-1];
	p += 4;
	}

	/* Finish the aligned tail. */
	t \|= e[-3];
	t \|= e[-2];
	t \|= e[-1];

	/* Finish the unaligned tail. */
	t \|= _mm_loadu_si128(buf + len - 16);

	return _mm_movemask_epi8(_mm_cmpeq_epi8(t, zero)) == 0xFFFF;
	}

	#ifdef CONFIG_AVX2_OPT
	static bool __attribute__((target("sse4")))
	buffer_zero_sse4(const void *buf, size_t len)
	{
	__m128i t = _mm_loadu_si128(buf);
	__m128i p = (__m128i )(((uintptr_t)buf + 5 * 16) & -16);
	__m128i e = (__m128i )(((uintptr_t)buf + len) & -16);

	/* Loop over 16-byte aligned blocks of 64. */
	while (likely(p <= e)) {
	__builtin_prefetch(p);
	if (unlikely(!_mm_testz_si128(t, t))) {
	return false;
	}
	t = p[-4] \| p[-3] \| p[-2] \| p[-1];
	p += 4;
	}

	/* Finish the aligned tail. */
	t \|= e[-3];
	t \|= e[-2];
	t \|= e[-1];

	/* Finish the unaligned tail. */
	t \|= _mm_loadu_si128(buf + len - 16);

	return _mm_testz_si128(t, t);
	}

	static bool __attribute__((target("avx2")))
	buffer_zero_avx2(const void *buf, size_t len)
	{
	/* Begin with an unaligned head of 32 bytes. */
	__m256i t = _mm256_loadu_si256(buf);
	__m256i p = (__m256i )(((uintptr_t)buf + 5 * 32) & -32);
	__m256i e = (__m256i )(((uintptr_t)buf + len) & -32);

	/* Loop over 32-byte aligned blocks of 128. */
	while (p <= e) {
	__builtin_prefetch(p);
	if (unlikely(!_mm256_testz_si256(t, t))) {
	return false;
	}
	t = p[-4] \| p[-3] \| p[-2] \| p[-1];
	p += 4;
	} ;

	/* Finish the last block of 128 unaligned. */
	t \|= _mm256_loadu_si256(buf + len - 4 * 32);
	t \|= _mm256_loadu_si256(buf + len - 3 * 32);
	t \|= _mm256_loadu_si256(buf + len - 2 * 32);
	t \|= _mm256_loadu_si256(buf + len - 1 * 32);

	return _mm256_testz_si256(t, t);
	}
	#endif /* CONFIG_AVX2_OPT */

	#ifdef CONFIG_AVX512F_OPT
	static bool __attribute__((target("avx512f")))
	buffer_zero_avx512(const void *buf, size_t len)
	{
	/* Begin with an unaligned head of 64 bytes. */
	__m512i t = _mm512_loadu_si512(buf);
	__m512i p = (__m512i )(((uintptr_t)buf + 5 * 64) & -64);
	__m512i e = (__m512i )(((uintptr_t)buf + len) & -64);

	/* Loop over 64-byte aligned blocks of 256. */
	while (p <= e) {
	__builtin_prefetch(p);
	if (unlikely(_mm512_test_epi64_mask(t, t))) {
	return false;
	}
	t = p[-4] \| p[-3] \| p[-2] \| p[-1];
	p += 4;
	}

	t \|= _mm512_loadu_si512(buf + len - 4 * 64);
	t \|= _mm512_loadu_si512(buf + len - 3 * 64);
	t \|= _mm512_loadu_si512(buf + len - 2 * 64);
	t \|= _mm512_loadu_si512(buf + len - 1 * 64);

	return !_mm512_test_epi64_mask(t, t);

	}
	#endif /* CONFIG_AVX512F_OPT */

	/*
	* Make sure that these variables are appropriately initialized when
	* SSE2 is enabled on the compiler command-line, but the compiler is
	* too old to support CONFIG_AVX2_OPT.
	*/
	#if defined(CONFIG_AVX512F_OPT) \|\| defined(CONFIG_AVX2_OPT)
	# define INIT_USED 0
	# define INIT_LENGTH 0
	# define INIT_ACCEL buffer_zero_int
	#else
	# ifndef __SSE2__
	# error "ISA selection confusion"
	# endif
	# define INIT_USED CPUINFO_SSE2
	# define INIT_LENGTH 64
	# define INIT_ACCEL buffer_zero_sse2
	#endif

	static unsigned used_accel = INIT_USED;
	static unsigned length_to_accel = INIT_LENGTH;
	static bool (buffer_accel)(const void , size_t) = INIT_ACCEL;

	static unsigned __attribute__((noinline))
	select_accel_cpuinfo(unsigned info)
	{
	/* Array is sorted in order of algorithm preference. */
	static const struct {
	unsigned bit;
	unsigned len;
	bool (fn)(const void , size_t);
	} all[] = {
	#ifdef CONFIG_AVX512F_OPT
	{ CPUINFO_AVX512F, 256, buffer_zero_avx512 },
	#endif
	#ifdef CONFIG_AVX2_OPT
	{ CPUINFO_AVX2, 128, buffer_zero_avx2 },
	{ CPUINFO_SSE4, 64, buffer_zero_sse4 },
	#endif
	{ CPUINFO_SSE2, 64, buffer_zero_sse2 },
	{ CPUINFO_ALWAYS, 0, buffer_zero_int },
	};

	for (unsigned i = 0; i < ARRAY_SIZE(all); ++i) {
	if (info & all[i].bit) {
	length_to_accel = all[i].len;
	buffer_accel = all[i].fn;
	return all[i].bit;
	}
	}
	return 0;
	}

	#if defined(CONFIG_AVX512F_OPT) \|\| defined(CONFIG_AVX2_OPT)
	static void __attribute__((constructor)) init_accel(void)
	{
	used_accel = select_accel_cpuinfo(cpuinfo_init());
	}
	#endif /* CONFIG_AVX2_OPT */

	bool test_buffer_is_zero_next_accel(void)
	{
	/*
	* Accumulate the accelerators that we've already tested, and
	* remove them from the set to test this round. We'll get back
	* a zero from select_accel_cpuinfo when there are no more.
	*/
	unsigned used = select_accel_cpuinfo(cpuinfo & ~used_accel);
	used_accel \|= used;
	return used;
	}

	static bool select_accel_fn(const void *buf, size_t len)
	{
	if (likely(len >= length_to_accel)) {
	return buffer_accel(buf, len);
	}
	return buffer_zero_int(buf, len);
	}

	#else
	#define select_accel_fn buffer_zero_int
	bool test_buffer_is_zero_next_accel(void)
	{
	return false;
	}
	#endif

	/*
	* Checks if a buffer is all zeroes
	*/
	bool buffer_is_zero(const void *buf, size_t len)
	{
	if (unlikely(len == 0)) {
	return true;
	}

	/* Fetch the beginning of the buffer while we select the accelerator. */
	__builtin_prefetch(buf);

	/* Use an optimized zero check if possible. Note that this also
	includes a check for an unrolled loop over 64-bit integers. */
	return select_accel_fn(buf, len);
	}