Hello
This patch adds support for 8- and 16-bit sync_compare_and_swap
operations on AMD GCN. GCN does not natively support atomic compare and
swap for quantities smaller than 32-bit words, so the subword compare
and swap is implemented in terms of 32-bit compare and swap.
The algorithm is similar to that on other architectures (e.g.
SUBWORD_SYNC_OP in libgcc/config/arm/linux-atomic.c). i.e. It reads from
memory the word containing the subword, creates a new word by replacing
the subword with the swap value, then does a 32-bit atomic compare and
swap with the old and new words. If the operation is unsuccessful due to
a part of the word that is not the target subword changing values since
the last read, then it must try again using the updated word.
Okay for trunk?
Kwok
2020-01-08 Kwok Cheung Yeung <k...@codesourcery.com>
libgcc/
* config/gcn/atomic.c: New.
* config/gcn/t-amdgcn (LIB2ADD): Add atomic.c.
---
libgcc/config/gcn/atomic.c | 60
++++++++++++++++++++++++++++++++++++++++++++++
libgcc/config/gcn/t-amdgcn | 3 ++-
2 files changed, 62 insertions(+), 1 deletion(-)
create mode 100644 libgcc/config/gcn/atomic.c
diff --git a/libgcc/config/gcn/atomic.c b/libgcc/config/gcn/atomic.c
new file mode 100644
index 0000000..6514dfc
--- /dev/null
+++ b/libgcc/config/gcn/atomic.c
@@ -0,0 +1,60 @@
+/* AMD GCN atomic operations
+ Copyright (C) 2020 Free Software Foundation, Inc.
+ Contributed by Mentor Graphics.
+
+ This file is free software; you can redistribute it and/or modify it
+ under the terms of the GNU General Public License as published by the
+ Free Software Foundation; either version 3, or (at your option) any
+ later version.
+
+ This file is distributed in the hope that it will be useful, but
+ WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ General Public License for more details.
+
+ Under Section 7 of GPL version 3, you are granted additional
+ permissions described in the GCC Runtime Library Exception, version
+ 3.1, as published by the Free Software Foundation.
+
+ You should have received a copy of the GNU General Public License and
+ a copy of the GCC Runtime Library Exception along with this program;
+ see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
+ <http://www.gnu.org/licenses/>. */
+
+#include <stdbool.h>
+
+#define __sync_subword_compare_and_swap(type, size) \
+ \
+type \
+__sync_val_compare_and_swap_##size (type *ptr, type oldval, type
newval) \
+{ \
+ unsigned int *wordptr
\
+ = (unsigned int *)((unsigned long long) ptr & ~3ULL);
\
+ int shift = ((unsigned long long) ptr & 3ULL) * 8;
\
+ unsigned int valmask = (1 << (size * 8)) - 1; \
+ unsigned int wordmask = ~(valmask << shift); \
+ unsigned int oldword = *wordptr; \
+ for (;;) \
+ { \
+ type prevval = (oldword >> shift) & valmask; \
+ if (__builtin_expect (prevval != oldval, 0)) \
+ return prevval; \
+ unsigned int newword = oldword & wordmask; \
+ newword |= ((unsigned int) newval) << shift; \
+ unsigned int prevword \
+ = __sync_val_compare_and_swap_4 (wordptr, oldword, newword); \
+ if (__builtin_expect (prevword == oldword, 1)) \
+ return oldval; \
+ oldword = prevword; \
+ } \
+} \
+ \
+bool \
+__sync_bool_compare_and_swap_##size (type *ptr, type oldval, type
newval) \
+{ \
+ return __sync_val_compare_and_swap_##size(ptr, oldval, newval) ==
oldval; \
+}
+
+__sync_subword_compare_and_swap (unsigned char, 1)
+__sync_subword_compare_and_swap (unsigned short, 2)
+
diff --git a/libgcc/config/gcn/t-amdgcn b/libgcc/config/gcn/t-amdgcn
index adbd866..fe7b5fa 100644
--- a/libgcc/config/gcn/t-amdgcn
+++ b/libgcc/config/gcn/t-amdgcn
@@ -1,4 +1,5 @@
-LIB2ADD += $(srcdir)/config/gcn/lib2-divmod.c \
+LIB2ADD += $(srcdir)/config/gcn/atomic.c \
+ $(srcdir)/config/gcn/lib2-divmod.c \
$(srcdir)/config/gcn/lib2-divmod-hi.c \
$(srcdir)/config/gcn/unwind-gcn.c
--
2.8.1
