78 lines
3.5 KiB
C
78 lines
3.5 KiB
C
/* NVPTX atomic operations
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Copyright (C) 2020-2021 Free Software Foundation, Inc.
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Contributed by Mentor Graphics.
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This file is free software; you can redistribute it and/or modify it
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under the terms of the GNU General Public License as published by the
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Free Software Foundation; either version 3, or (at your option) any
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later version.
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This file is distributed in the hope that it will be useful, but
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WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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General Public License for more details.
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Under Section 7 of GPL version 3, you are granted additional
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permissions described in the GCC Runtime Library Exception, version
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3.1, as published by the Free Software Foundation.
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You should have received a copy of the GNU General Public License and
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a copy of the GCC Runtime Library Exception along with this program;
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see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
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<http://www.gnu.org/licenses/>. */
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#include <stdbool.h>
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/* Implement __sync_val_compare_and_swap and __sync_bool_compare_and_swap
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for 1 and 2-byte values (which are not natively supported) in terms of
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__sync_val_compare_and_swap for 4-byte values (which is supported).
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This assumes that the contents of the word surrounding the subword
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value that we are interested in are accessible as well (which should
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normally be the case). Note that if the contents of the word surrounding
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the subword changes between the __sync_val_compare_and_swap_4 and the
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preceeding load of oldword, while the subword does not, the implementation
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loops, which may manifest worst-case as a hang. */
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#define __SYNC_SUBWORD_COMPARE_AND_SWAP(TYPE, SIZE) \
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\
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TYPE \
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__sync_val_compare_and_swap_##SIZE (volatile void *vptr, TYPE oldval, \
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TYPE newval) \
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{ \
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volatile TYPE *ptr = vptr; \
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volatile unsigned int *wordptr \
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= (volatile unsigned int *)((__UINTPTR_TYPE__) ptr & ~3UL); \
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int shift = ((__UINTPTR_TYPE__) ptr & 3UL) * 8; \
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unsigned int valmask = (1 << (SIZE * 8)) - 1; \
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unsigned int wordmask = ~(valmask << shift); \
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unsigned int oldword = *wordptr; \
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for (;;) \
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{ \
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TYPE prevval = (oldword >> shift) & valmask; \
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/* Exit if the subword value previously read from memory is not */ \
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/* equal to the expected value OLDVAL. */ \
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if (__builtin_expect (prevval != oldval, 0)) \
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return prevval; \
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unsigned int newword = oldword & wordmask; \
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newword |= ((unsigned int) newval) << shift; \
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unsigned int prevword \
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= __sync_val_compare_and_swap_4 (wordptr, oldword, newword); \
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/* Exit only if the compare-and-swap succeeds on the whole word */ \
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/* (i.e. the contents of *WORDPTR have not changed since the last */ \
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/* memory read). */ \
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if (__builtin_expect (prevword == oldword, 1)) \
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return oldval; \
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oldword = prevword; \
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} \
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} \
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\
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bool \
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__sync_bool_compare_and_swap_##SIZE (volatile void *ptr, TYPE oldval, \
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TYPE newval) \
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{ \
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return __sync_val_compare_and_swap_##SIZE (ptr, oldval, newval) == oldval; \
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}
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__SYNC_SUBWORD_COMPARE_AND_SWAP (unsigned char, 1)
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__SYNC_SUBWORD_COMPARE_AND_SWAP (unsigned short, 2)
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