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GCC Code Coverage Report

Directory:	./		Exec	Total	Coverage
File:	lib/libcompiler_rt/atomic.c	Lines:	0	43	0.0 %
Date:	2017-11-13	Branches:	0	457	0.0 %


/*===-- atomic.c - Implement support functions for atomic operations.------===
 *
 *                     The LLVM Compiler Infrastructure
 *
 * This file is dual licensed under the MIT and the University of Illinois Open
 * Source Licenses. See LICENSE.TXT for details.
 *
 *===----------------------------------------------------------------------===
 *
 *  atomic.c defines a set of functions for performing atomic accesses on
 *  arbitrary-sized memory locations.  This design uses locks that should
 *  be fast in the uncontended case, for two reasons:
 *
 *  1) This code must work with C programs that do not link to anything
 *     (including pthreads) and so it should not depend on any pthread
 *     functions.
 *  2) Atomic operations, rather than explicit mutexes, are most commonly used
 *     on code where contended operations are rate.
 *
 *  To avoid needing a per-object lock, this code allocates an array of
 *  locks and hashes the object pointers to find the one that it should use.
 *  For operations that must be atomic on two locations, the lower lock is
 *  always acquired first, to avoid deadlock.
 *
 *===----------------------------------------------------------------------===
 */

#include <stdint.h>
#include <string.h>

#include "assembly.h"

// Clang objects if you redefine a builtin.  This little hack allows us to
// define a function with the same name as an intrinsic.
#pragma redefine_extname __atomic_load_c SYMBOL_NAME(__atomic_load)
#pragma redefine_extname __atomic_store_c SYMBOL_NAME(__atomic_store)
#pragma redefine_extname __atomic_exchange_c SYMBOL_NAME(__atomic_exchange)
#pragma redefine_extname __atomic_compare_exchange_c SYMBOL_NAME(__atomic_compare_exchange)

/// Number of locks.  This allocates one page on 32-bit platforms, two on
/// 64-bit.  This can be specified externally if a different trade between
/// memory usage and contention probability is required for a given platform.
#ifndef SPINLOCK_COUNT
#define SPINLOCK_COUNT (1<<10)
#endif
static const long SPINLOCK_MASK = SPINLOCK_COUNT - 1;

////////////////////////////////////////////////////////////////////////////////
// Platform-specific lock implementation.  Falls back to spinlocks if none is
// defined.  Each platform should define the Lock type, and corresponding
// lock() and unlock() functions.
////////////////////////////////////////////////////////////////////////////////
#ifdef __FreeBSD__
#include <errno.h>
#include <sys/types.h>
#include <machine/atomic.h>
#include <sys/umtx.h>
typedef struct _usem Lock;
__inline static void unlock(Lock *l) {
  __c11_atomic_store((_Atomic(uint32_t)*)&l->_count, 1, __ATOMIC_RELEASE);
  __c11_atomic_thread_fence(__ATOMIC_SEQ_CST);
  if (l->_has_waiters)
      _umtx_op(l, UMTX_OP_SEM_WAKE, 1, 0, 0);
}
__inline static void lock(Lock *l) {
  uint32_t old = 1;
  while (!__c11_atomic_compare_exchange_weak((_Atomic(uint32_t)*)&l->_count, &old,
        0, __ATOMIC_ACQUIRE, __ATOMIC_RELAXED)) {
    _umtx_op(l, UMTX_OP_SEM_WAIT, 0, 0, 0);
    old = 1;
  }
}
/// locks for atomic operations
static Lock locks[SPINLOCK_COUNT] = { [0 ...  SPINLOCK_COUNT-1] = {0,1,0} };

#elif defined(__APPLE__)
#include <libkern/OSAtomic.h>
typedef OSSpinLock Lock;
__inline static void unlock(Lock *l) {
  OSSpinLockUnlock(l);
}
/// Locks a lock.  In the current implementation, this is potentially
/// unbounded in the contended case.
__inline static void lock(Lock *l) {
  OSSpinLockLock(l);
}
static Lock locks[SPINLOCK_COUNT]; // initialized to OS_SPINLOCK_INIT which is 0

#else
typedef _Atomic(uintptr_t) Lock;
/// Unlock a lock.  This is a release operation.
__inline static void unlock(Lock *l) {
  __c11_atomic_store(l, 0, __ATOMIC_RELEASE);
}
/// Locks a lock.  In the current implementation, this is potentially
/// unbounded in the contended case.
__inline static void lock(Lock *l) {
  uintptr_t old = 0;
  while (!__c11_atomic_compare_exchange_weak(l, &old, 1, __ATOMIC_ACQUIRE,
        __ATOMIC_RELAXED))
    old = 0;
}
/// locks for atomic operations
static Lock locks[SPINLOCK_COUNT];
#endif


/// Returns a lock to use for a given pointer.
static __inline Lock *lock_for_pointer(void *ptr) {
  intptr_t hash = (intptr_t)ptr;
  // Disregard the lowest 4 bits.  We want all values that may be part of the
  // same memory operation to hash to the same value and therefore use the same
  // lock.
  hash >>= 4;
  // Use the next bits as the basis for the hash
  intptr_t low = hash & SPINLOCK_MASK;
  // Now use the high(er) set of bits to perturb the hash, so that we don't
  // get collisions from atomic fields in a single object
  hash >>= 16;
  hash ^= low;
  // Return a pointer to the word to use
  return locks + (hash & SPINLOCK_MASK);
}

/// Macros for determining whether a size is lock free.  Clang can not yet
/// codegen __atomic_is_lock_free(16), so for now we assume 16-byte values are
/// not lock free.
#define IS_LOCK_FREE_1 __c11_atomic_is_lock_free(1)
#define IS_LOCK_FREE_2 __c11_atomic_is_lock_free(2)
#define IS_LOCK_FREE_4 __c11_atomic_is_lock_free(4)
#define IS_LOCK_FREE_8 __c11_atomic_is_lock_free(8)
#define IS_LOCK_FREE_16 0

/// Macro that calls the compiler-generated lock-free versions of functions
/// when they exist.
#define LOCK_FREE_CASES() \
  do {\
  switch (size) {\
    case 2:\
      if (IS_LOCK_FREE_2) {\
        LOCK_FREE_ACTION(uint16_t);\
      }\
    case 4:\
      if (IS_LOCK_FREE_4) {\
        LOCK_FREE_ACTION(uint32_t);\
      }\
    case 8:\
      if (IS_LOCK_FREE_8) {\
        LOCK_FREE_ACTION(uint64_t);\
      }\
    case 16:\
      if (IS_LOCK_FREE_16) {\
        /* FIXME: __uint128_t isn't available on 32 bit platforms.
        LOCK_FREE_ACTION(__uint128_t);*/\
      }\
  }\
  } while (0)


/// An atomic load operation.  This is atomic with respect to the source
/// pointer only.
void __atomic_load_c(int size, void *src, void *dest, int model) {
#define LOCK_FREE_ACTION(type) \
    *((type*)dest) = __c11_atomic_load((_Atomic(type)*)src, model);\
    return;
  LOCK_FREE_CASES();
#undef LOCK_FREE_ACTION
  Lock *l = lock_for_pointer(src);
  lock(l);
  memcpy(dest, src, size);
  unlock(l);
}

/// An atomic store operation.  This is atomic with respect to the destination
/// pointer only.
void __atomic_store_c(int size, void *dest, void *src, int model) {
#define LOCK_FREE_ACTION(type) \
    __c11_atomic_store((_Atomic(type)*)dest, *(type*)dest, model);\
    return;
  LOCK_FREE_CASES();
#undef LOCK_FREE_ACTION
  Lock *l = lock_for_pointer(dest);
  lock(l);
  memcpy(dest, src, size);
  unlock(l);
}

/// Atomic compare and exchange operation.  If the value at *ptr is identical
/// to the value at *expected, then this copies value at *desired to *ptr.  If
/// they  are not, then this stores the current value from *ptr in *expected.
///
/// This function returns 1 if the exchange takes place or 0 if it fails.
int __atomic_compare_exchange_c(int size, void *ptr, void *expected,
    void *desired, int success, int failure) {
#define LOCK_FREE_ACTION(type) \
  return __c11_atomic_compare_exchange_strong((_Atomic(type)*)ptr, (type*)expected,\
      *(type*)desired, success, failure)
  LOCK_FREE_CASES();
#undef LOCK_FREE_ACTION
  Lock *l = lock_for_pointer(ptr);
  lock(l);
  if (memcmp(ptr, expected, size) == 0) {
    memcpy(ptr, desired, size);
    unlock(l);
    return 1;
  }
  memcpy(expected, ptr, size);
  unlock(l);
  return 0;
}

/// Performs an atomic exchange operation between two pointers.  This is atomic
/// with respect to the target address.
void __atomic_exchange_c(int size, void *ptr, void *val, void *old, int model) {
#define LOCK_FREE_ACTION(type) \
    *(type*)old = __c11_atomic_exchange((_Atomic(type)*)ptr, *(type*)val,\
        model);\
    return;
  LOCK_FREE_CASES();
#undef LOCK_FREE_ACTION
  Lock *l = lock_for_pointer(ptr);
  lock(l);
  memcpy(old, ptr, size);
  memcpy(ptr, val, size);
  unlock(l);
}

////////////////////////////////////////////////////////////////////////////////
// Where the size is known at compile time, the compiler may emit calls to
// specialised versions of the above functions.
////////////////////////////////////////////////////////////////////////////////
#define OPTIMISED_CASES\
  OPTIMISED_CASE(1, IS_LOCK_FREE_1, uint8_t)\
  OPTIMISED_CASE(2, IS_LOCK_FREE_2, uint16_t)\
  OPTIMISED_CASE(4, IS_LOCK_FREE_4, uint32_t)\
  OPTIMISED_CASE(8, IS_LOCK_FREE_8, uint64_t)\
  /* FIXME: __uint128_t isn't available on 32 bit platforms.
  OPTIMISED_CASE(16, IS_LOCK_FREE_16, __uint128_t)*/\

#define OPTIMISED_CASE(n, lockfree, type)\
type __atomic_load_##n(type *src, int model) {\
  if (lockfree)\
    return __c11_atomic_load((_Atomic(type)*)src, model);\
  Lock *l = lock_for_pointer(src);\
  lock(l);\
  type val = *src;\
  unlock(l);\
  return val;\
}
OPTIMISED_CASES
#undef OPTIMISED_CASE

#define OPTIMISED_CASE(n, lockfree, type)\
void  __atomic_store_##n(type *dest, type val, int model) {\
  if (lockfree) {\
    __c11_atomic_store((_Atomic(type)*)dest, val, model);\
    return;\
  }\
  Lock *l = lock_for_pointer(dest);\
  lock(l);\
  *dest = val;\
  unlock(l);\
  return;\
}
OPTIMISED_CASES
#undef OPTIMISED_CASE

#define OPTIMISED_CASE(n, lockfree, type)\
type __atomic_exchange_##n(type *dest, type val, int model) {\
  if (lockfree)\
    return __c11_atomic_exchange((_Atomic(type)*)dest, val, model);\
  Lock *l = lock_for_pointer(dest);\
  lock(l);\
  type tmp = *dest;\
  *dest = val;\
  unlock(l);\
  return tmp;\
}
OPTIMISED_CASES
#undef OPTIMISED_CASE

#define OPTIMISED_CASE(n, lockfree, type)\
int __atomic_compare_exchange_##n(type *ptr, type *expected, type desired,\
    int success, int failure) {\
  if (lockfree)\
    return __c11_atomic_compare_exchange_strong((_Atomic(type)*)ptr, expected, desired,\
        success, failure);\
  Lock *l = lock_for_pointer(ptr);\
  lock(l);\
  if (*ptr == *expected) {\
    *ptr = desired;\
    unlock(l);\
    return 1;\
  }\
  *expected = *ptr;\
  unlock(l);\
  return 0;\
}
OPTIMISED_CASES
#undef OPTIMISED_CASE

////////////////////////////////////////////////////////////////////////////////
// Atomic read-modify-write operations for integers of various sizes.
////////////////////////////////////////////////////////////////////////////////
#define ATOMIC_RMW(n, lockfree, type, opname, op) \
type __atomic_fetch_##opname##_##n(type *ptr, type val, int model) {\
  if (lockfree) \
    return __c11_atomic_fetch_##opname((_Atomic(type)*)ptr, val, model);\
  Lock *l = lock_for_pointer(ptr);\
  lock(l);\
  type tmp = *ptr;\
  *ptr = tmp op val;\
  unlock(l);\
  return tmp;\
}

#define OPTIMISED_CASE(n, lockfree, type) ATOMIC_RMW(n, lockfree, type, add, +)
OPTIMISED_CASES
#undef OPTIMISED_CASE
#define OPTIMISED_CASE(n, lockfree, type) ATOMIC_RMW(n, lockfree, type, sub, -)
OPTIMISED_CASES
#undef OPTIMISED_CASE
#define OPTIMISED_CASE(n, lockfree, type) ATOMIC_RMW(n, lockfree, type, and, &)
OPTIMISED_CASES
#undef OPTIMISED_CASE
#define OPTIMISED_CASE(n, lockfree, type) ATOMIC_RMW(n, lockfree, type, or, |)
OPTIMISED_CASES
#undef OPTIMISED_CASE
#define OPTIMISED_CASE(n, lockfree, type) ATOMIC_RMW(n, lockfree, type, xor, ^)
OPTIMISED_CASES
#undef OPTIMISED_CASE


Generated by: GCOVR (Version 3.3)

Line	Branch	Exec	Source
1			/*===-- atomic.c - Implement support functions for atomic operations.------===
2			*
3			* The LLVM Compiler Infrastructure
4			*
5			* This file is dual licensed under the MIT and the University of Illinois Open
6			* Source Licenses. See LICENSE.TXT for details.
7			*
8			*===----------------------------------------------------------------------===
9			*
10			* atomic.c defines a set of functions for performing atomic accesses on
11			* arbitrary-sized memory locations. This design uses locks that should
12			* be fast in the uncontended case, for two reasons:
13			*
14			* 1) This code must work with C programs that do not link to anything
15			* (including pthreads) and so it should not depend on any pthread
16			* functions.
17			* 2) Atomic operations, rather than explicit mutexes, are most commonly used
18			* on code where contended operations are rate.
19			*
20			* To avoid needing a per-object lock, this code allocates an array of
21			* locks and hashes the object pointers to find the one that it should use.
22			* For operations that must be atomic on two locations, the lower lock is
23			* always acquired first, to avoid deadlock.
24			*
25			*===----------------------------------------------------------------------===
26			*/
27
28			#include <stdint.h>
29			#include <string.h>
30
31			#include "assembly.h"
32
33			// Clang objects if you redefine a builtin. This little hack allows us to
34			// define a function with the same name as an intrinsic.
35			#pragma redefine_extname __atomic_load_c SYMBOL_NAME(__atomic_load)
36			#pragma redefine_extname __atomic_store_c SYMBOL_NAME(__atomic_store)
37			#pragma redefine_extname __atomic_exchange_c SYMBOL_NAME(__atomic_exchange)
38			#pragma redefine_extname __atomic_compare_exchange_c SYMBOL_NAME(__atomic_compare_exchange)
39
40			/// Number of locks. This allocates one page on 32-bit platforms, two on
41			/// 64-bit. This can be specified externally if a different trade between
42			/// memory usage and contention probability is required for a given platform.
43			#ifndef SPINLOCK_COUNT
44			#define SPINLOCK_COUNT (1<<10)
45			#endif
46			static const long SPINLOCK_MASK = SPINLOCK_COUNT - 1;
47
48			////////////////////////////////////////////////////////////////////////////////
49			// Platform-specific lock implementation. Falls back to spinlocks if none is
50			// defined. Each platform should define the Lock type, and corresponding
51			// lock() and unlock() functions.
52			////////////////////////////////////////////////////////////////////////////////
53			#ifdef __FreeBSD__
54			#include <errno.h>
55			#include <sys/types.h>
56			#include <machine/atomic.h>
57			#include <sys/umtx.h>
58			typedef struct _usem Lock;
59			__inline static void unlock(Lock *l) {
60			__c11_atomic_store((_Atomic(uint32_t)*)&l->_count, 1, __ATOMIC_RELEASE);
61			__c11_atomic_thread_fence(__ATOMIC_SEQ_CST);
62			if (l->_has_waiters)
63			_umtx_op(l, UMTX_OP_SEM_WAKE, 1, 0, 0);
64			}
65			__inline static void lock(Lock *l) {
66			uint32_t old = 1;
67			while (!__c11_atomic_compare_exchange_weak((_Atomic(uint32_t)*)&l->_count, &old,
68			0, __ATOMIC_ACQUIRE, __ATOMIC_RELAXED)) {
69			_umtx_op(l, UMTX_OP_SEM_WAIT, 0, 0, 0);
70			old = 1;
71			}
72			}
73			/// locks for atomic operations
74			static Lock locks[SPINLOCK_COUNT] = { [0 ... SPINLOCK_COUNT-1] = {0,1,0} };
75
76			#elif defined(__APPLE__)
77			#include <libkern/OSAtomic.h>
78			typedef OSSpinLock Lock;
79			__inline static void unlock(Lock *l) {
80			OSSpinLockUnlock(l);
81			}
82			/// Locks a lock. In the current implementation, this is potentially
83			/// unbounded in the contended case.
84			__inline static void lock(Lock *l) {
85			OSSpinLockLock(l);
86			}
87			static Lock locks[SPINLOCK_COUNT]; // initialized to OS_SPINLOCK_INIT which is 0
88
89			#else
90			typedef _Atomic(uintptr_t) Lock;
91			/// Unlock a lock. This is a release operation.
92			__inline static void unlock(Lock *l) {
93			__c11_atomic_store(l, 0, __ATOMIC_RELEASE);
94			}
95			/// Locks a lock. In the current implementation, this is potentially
96			/// unbounded in the contended case.
97			__inline static void lock(Lock *l) {
98			uintptr_t old = 0;
99			while (!__c11_atomic_compare_exchange_weak(l, &old, 1, __ATOMIC_ACQUIRE,
100			__ATOMIC_RELAXED))
101			old = 0;
102			}
103			/// locks for atomic operations
104			static Lock locks[SPINLOCK_COUNT];
105			#endif
106
107
108			/// Returns a lock to use for a given pointer.
109			static __inline Lock lock_for_pointer(void ptr) {
110			intptr_t hash = (intptr_t)ptr;
111			// Disregard the lowest 4 bits. We want all values that may be part of the
112			// same memory operation to hash to the same value and therefore use the same
113			// lock.
114			hash >>= 4;
115			// Use the next bits as the basis for the hash
116			intptr_t low = hash & SPINLOCK_MASK;
117			// Now use the high(er) set of bits to perturb the hash, so that we don't
118			// get collisions from atomic fields in a single object
119			hash >>= 16;
120			hash ^= low;
121			// Return a pointer to the word to use
122			return locks + (hash & SPINLOCK_MASK);
123			}
124
125			/// Macros for determining whether a size is lock free. Clang can not yet
126			/// codegen __atomic_is_lock_free(16), so for now we assume 16-byte values are
127			/// not lock free.
128			#define IS_LOCK_FREE_1 __c11_atomic_is_lock_free(1)
129			#define IS_LOCK_FREE_2 __c11_atomic_is_lock_free(2)
130			#define IS_LOCK_FREE_4 __c11_atomic_is_lock_free(4)
131			#define IS_LOCK_FREE_8 __c11_atomic_is_lock_free(8)
132			#define IS_LOCK_FREE_16 0
133
134			/// Macro that calls the compiler-generated lock-free versions of functions
135			/// when they exist.
136			#define LOCK_FREE_CASES() \
137			do {\
138			switch (size) {\
139			case 2:\
140			if (IS_LOCK_FREE_2) {\
141			LOCK_FREE_ACTION(uint16_t);\
142			}\
143			case 4:\
144			if (IS_LOCK_FREE_4) {\
145			LOCK_FREE_ACTION(uint32_t);\
146			}\
147			case 8:\
148			if (IS_LOCK_FREE_8) {\
149			LOCK_FREE_ACTION(uint64_t);\
150			}\
151			case 16:\
152			if (IS_LOCK_FREE_16) {\
153			/* FIXME: __uint128_t isn't available on 32 bit platforms.
154			LOCK_FREE_ACTION(__uint128_t);*/\
155			}\
156			}\
157			} while (0)
158
159
160			/// An atomic load operation. This is atomic with respect to the source
161			/// pointer only.
162			void __atomic_load_c(int size, void src, void dest, int model) {
163			#define LOCK_FREE_ACTION(type) \
164			((type)dest) = __c11_atomic_load((_Atomic(type)*)src, model);\
165			return;
166			LOCK_FREE_CASES();
167			#undef LOCK_FREE_ACTION
168			Lock *l = lock_for_pointer(src);
169			lock(l);
170			memcpy(dest, src, size);
171			unlock(l);
172			}
173
174			/// An atomic store operation. This is atomic with respect to the destination
175			/// pointer only.
176			void __atomic_store_c(int size, void dest, void src, int model) {
177			#define LOCK_FREE_ACTION(type) \
178			__c11_atomic_store((_Atomic(type))dest, (type*)dest, model);\
179			return;
180			LOCK_FREE_CASES();
181			#undef LOCK_FREE_ACTION
182			Lock *l = lock_for_pointer(dest);
183			lock(l);
184			memcpy(dest, src, size);
185			unlock(l);
186			}
187
188			/// Atomic compare and exchange operation. If the value at *ptr is identical
189			/// to the value at expected, then this copies value at desired to *ptr. If
190			/// they are not, then this stores the current value from ptr in expected.
191			///
192			/// This function returns 1 if the exchange takes place or 0 if it fails.
193			int __atomic_compare_exchange_c(int size, void ptr, void expected,
194			void *desired, int success, int failure) {
195			#define LOCK_FREE_ACTION(type) \
196			return __c11_atomic_compare_exchange_strong((_Atomic(type))ptr, (type)expected,\
197			(type)desired, success, failure)
198			LOCK_FREE_CASES();
199			#undef LOCK_FREE_ACTION
200			Lock *l = lock_for_pointer(ptr);
201			lock(l);
202			if (memcmp(ptr, expected, size) == 0) {
203			memcpy(ptr, desired, size);
204			unlock(l);
205			return 1;
206			}
207			memcpy(expected, ptr, size);
208			unlock(l);
209			return 0;
210			}
211
212			/// Performs an atomic exchange operation between two pointers. This is atomic
213			/// with respect to the target address.
214			void __atomic_exchange_c(int size, void ptr, void val, void *old, int model) {
215			#define LOCK_FREE_ACTION(type) \
216			(type)old = __c11_atomic_exchange((_Atomic(type))ptr, (type*)val,\
217			model);\
218			return;
219			LOCK_FREE_CASES();
220			#undef LOCK_FREE_ACTION
221			Lock *l = lock_for_pointer(ptr);
222			lock(l);
223			memcpy(old, ptr, size);
224			memcpy(ptr, val, size);
225			unlock(l);
226			}
227
228			////////////////////////////////////////////////////////////////////////////////
229			// Where the size is known at compile time, the compiler may emit calls to
230			// specialised versions of the above functions.
231			////////////////////////////////////////////////////////////////////////////////
232			#define OPTIMISED_CASES\
233			OPTIMISED_CASE(1, IS_LOCK_FREE_1, uint8_t)\
234			OPTIMISED_CASE(2, IS_LOCK_FREE_2, uint16_t)\
235			OPTIMISED_CASE(4, IS_LOCK_FREE_4, uint32_t)\
236			OPTIMISED_CASE(8, IS_LOCK_FREE_8, uint64_t)\
237			/* FIXME: __uint128_t isn't available on 32 bit platforms.
238			OPTIMISED_CASE(16, IS_LOCK_FREE_16, __uint128_t)*/\
239
240			#define OPTIMISED_CASE(n, lockfree, type)\
241			type __atomic_load_##n(type *src, int model) {\
242			if (lockfree)\
243			return __c11_atomic_load((_Atomic(type)*)src, model);\
244			Lock *l = lock_for_pointer(src);\
245			lock(l);\
246			type val = *src;\
247			unlock(l);\
248			return val;\
249			}
250			OPTIMISED_CASES
251			#undef OPTIMISED_CASE
252
253			#define OPTIMISED_CASE(n, lockfree, type)\
254			void __atomic_store_##n(type *dest, type val, int model) {\
255			if (lockfree) {\
256			__c11_atomic_store((_Atomic(type)*)dest, val, model);\
257			return;\
258			}\
259			Lock *l = lock_for_pointer(dest);\
260			lock(l);\
261			*dest = val;\
262			unlock(l);\
263			return;\
264			}
265			OPTIMISED_CASES
266			#undef OPTIMISED_CASE
267
268			#define OPTIMISED_CASE(n, lockfree, type)\
269			type __atomic_exchange_##n(type *dest, type val, int model) {\
270			if (lockfree)\
271			return __c11_atomic_exchange((_Atomic(type)*)dest, val, model);\
272			Lock *l = lock_for_pointer(dest);\
273			lock(l);\
274			type tmp = *dest;\
275			*dest = val;\
276			unlock(l);\
277			return tmp;\
278			}
279			OPTIMISED_CASES
280			#undef OPTIMISED_CASE
281
282			#define OPTIMISED_CASE(n, lockfree, type)\
283			int __atomic_compare_exchange_##n(type ptr, type expected, type desired,\
284			int success, int failure) {\
285			if (lockfree)\
286			return __c11_atomic_compare_exchange_strong((_Atomic(type)*)ptr, expected, desired,\
287			success, failure);\
288			Lock *l = lock_for_pointer(ptr);\
289			lock(l);\
290			if (ptr == expected) {\
291			*ptr = desired;\
292			unlock(l);\
293			return 1;\
294			}\
295			expected = ptr;\
296			unlock(l);\
297			return 0;\
298			}
299			OPTIMISED_CASES
300			#undef OPTIMISED_CASE
301
302			////////////////////////////////////////////////////////////////////////////////
303			// Atomic read-modify-write operations for integers of various sizes.
304			////////////////////////////////////////////////////////////////////////////////
305			#define ATOMIC_RMW(n, lockfree, type, opname, op) \
306			type __atomic_fetch_##opname##_##n(type *ptr, type val, int model) {\
307			if (lockfree) \
308			return __c11_atomic_fetch_##opname((_Atomic(type)*)ptr, val, model);\
309			Lock *l = lock_for_pointer(ptr);\
310			lock(l);\
311			type tmp = *ptr;\
312			*ptr = tmp op val;\
313			unlock(l);\
314			return tmp;\
315			}
316
317			#define OPTIMISED_CASE(n, lockfree, type) ATOMIC_RMW(n, lockfree, type, add, +)
318			OPTIMISED_CASES
319			#undef OPTIMISED_CASE
320			#define OPTIMISED_CASE(n, lockfree, type) ATOMIC_RMW(n, lockfree, type, sub, -)
321			OPTIMISED_CASES
322			#undef OPTIMISED_CASE
323			#define OPTIMISED_CASE(n, lockfree, type) ATOMIC_RMW(n, lockfree, type, and, &)
324			OPTIMISED_CASES
325			#undef OPTIMISED_CASE
326			#define OPTIMISED_CASE(n, lockfree, type) ATOMIC_RMW(n, lockfree, type, or, \|)
327			OPTIMISED_CASES
328			#undef OPTIMISED_CASE
329			#define OPTIMISED_CASE(n, lockfree, type) ATOMIC_RMW(n, lockfree, type, xor, ^)
330			OPTIMISED_CASES
331			#undef OPTIMISED_CASE