[PATCH] nvptx: Add support for subword compare-and-swap

[Kwok Cheung Yeung <kcy@codesourcery.com>]

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Hello

This patch adds support on nvptx for __sync_val_compare_and_swap operations on 
1- and 2-byte values. The implementation is a straight copy of the version for 
AMD GCN.

I have added a new libgomp test that exercises the new operation. I have also 
verified that the new code does not cause any regressions on the nvptx 
offloading tests, and that the new test passes with both nvptx and amdgcn as 
offload targets.

Okay for master and OG10?

Kwok


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commit 7c3a9c23ba9f5b8fe953aa5492ae75617f2444a3
Author: Kwok Cheung Yeung <kcy@codesourcery.com>
Date:   Mon Jun 15 12:34:55 2020 -0700

    nvptx: Add support for subword compare-and-swap
    
    2020-06-15  Kwok Cheung Yeung  <kcy@codesourcery.com>
    
    	libgcc/
    	* config/nvptx/atomic.c: New.
    	* config/nvptx/t-nvptx (LIB2ADD): Add atomic.c.
    
    	libgomp/
    	* testsuite/libgomp.c-c++-common/reduction-16.c: New.

diff --git a/libgcc/config/nvptx/atomic.c b/libgcc/config/nvptx/atomic.c
new file mode 100644
index 0000000..4becbd2
--- /dev/null
+++ b/libgcc/config/nvptx/atomic.c
@@ -0,0 +1,59 @@
+/* NVPTX 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 *)((__UINTPTR_TYPE__ ) ptr & ~3UL);  \
+  int shift = ((__UINTPTR_TYPE__ ) ptr & 3UL) * 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/nvptx/t-nvptx b/libgcc/config/nvptx/t-nvptx
index c4d20c9..ede0bf0 100644
--- a/libgcc/config/nvptx/t-nvptx
+++ b/libgcc/config/nvptx/t-nvptx
@@ -1,5 +1,6 @@
 LIB2ADD=$(srcdir)/config/nvptx/reduction.c \
-	$(srcdir)/config/nvptx/mgomp.c
+	$(srcdir)/config/nvptx/mgomp.c \
+	$(srcdir)/config/nvptx/atomic.c
 
 LIB2ADDEH=
 LIB2FUNCS_EXCLUDE=__main
diff --git a/libgomp/testsuite/libgomp.c-c++-common/reduction-16.c b/libgomp/testsuite/libgomp.c-c++-common/reduction-16.c
new file mode 100644
index 0000000..951e522
--- /dev/null
+++ b/libgomp/testsuite/libgomp.c-c++-common/reduction-16.c
@@ -0,0 +1,46 @@
+/* { dg-do run } */
+
+#include <stdlib.h>
+
+#define N 512
+
+#define GENERATE_TEST(T)	\
+int test_##T (void)		\
+{				\
+  T a[N], res = 0;		\
+				\
+  for (int i = 0; i < N; ++i)	\
+    a[i] = i & 1;		\
+				\
+_Pragma("omp target teams distribute reduction(||:res) defaultmap(tofrom:scalar)") \
+  for (int i = 0; i < N; ++i)	\
+    res = res || a[i];		\
+				\
+  /* res should be non-zero.  */\
+  if (!res)			\
+    return 1;			\
+				\
+_Pragma("omp target teams distribute reduction(&&:res) defaultmap(tofrom:scalar)") \
+  for (int i = 0; i < N; ++i)	\
+    res = res && a[i];		\
+				\
+  /* res should be zero.  */	\
+  return res;			\
+}
+
+GENERATE_TEST(char)
+GENERATE_TEST(short)
+GENERATE_TEST(int)
+GENERATE_TEST(long)
+
+int main(void)
+{
+  if (test_char ())
+    abort ();
+  if (test_short ())
+    abort ();
+  if (test_int ())
+    abort ();
+  if (test_long ())
+    abort ();
+}