[PATCH, libgfortran] Replace sync builtins with atomic builtins

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[PATCH, libgfortran] Replace sync builtins with atomic builtins

Janne Blomqvist-3
The old __sync builtins have been deprecated for a long time now in
favor of the __atomic builtins following the C++11/C11 memory model.
This patch converts libgfortran to use the modern __atomic builtins.

At the same time I weakened the consistency to acquire-release as that
should be enough for this particular case.  Jakub, as the original
author of the algorithm, do you concur?

Regtested on x86_64-pc-linux-gnu, Ok for trunk?

libgfortran/ChangeLog:

2018-11-09  Janne Blomqvist  <[hidden email]>

        * acinclude.m4 (LIBGFOR_CHECK_ATOMIC_FETCH_ADD): Rename and test
        presence of atomic builtins instead of sync builtins.
        * configure.ac (LIBGFOR_CHECK_ATOMIC_FETCH_ADD): Call new test.
        * io/io.h (inc_waiting_locked): Use __atomic_fetch_add.
        (predec_waiting_locked): Use __atomic_add_fetch.
        (dec_waiting_unlocked): Use __atomic_fetch_add.
        * config.h.in: Regenerated.
        * configure: Regenerated.
---
 libgfortran/acinclude.m4 | 20 ++++++++++----------
 libgfortran/configure.ac |  4 ++--
 libgfortran/io/io.h      | 12 ++++++------
 3 files changed, 18 insertions(+), 18 deletions(-)

diff --git a/libgfortran/acinclude.m4 b/libgfortran/acinclude.m4
index dd5429ac0d2..5b0c094e716 100644
--- a/libgfortran/acinclude.m4
+++ b/libgfortran/acinclude.m4
@@ -59,17 +59,17 @@ extern void bar(void) __attribute__((alias("foo")));]],
       [Define to 1 if the target supports __attribute__((alias(...))).])
   fi])
 
-dnl Check whether the target supports __sync_fetch_and_add.
-AC_DEFUN([LIBGFOR_CHECK_SYNC_FETCH_AND_ADD], [
-  AC_CACHE_CHECK([whether the target supports __sync_fetch_and_add],
- libgfor_cv_have_sync_fetch_and_add, [
+dnl Check whether the target supports __atomic_fetch_add.
+AC_DEFUN([LIBGFOR_CHECK_ATOMIC_FETCH_ADD], [
+  AC_CACHE_CHECK([whether the target supports __atomic_fetch_add],
+ libgfor_cv_have_atomic_fetch_add, [
   AC_LINK_IFELSE([AC_LANG_PROGRAM([[int foovar = 0;]], [[
-if (foovar <= 0) return __sync_fetch_and_add (&foovar, 1);
-if (foovar > 10) return __sync_add_and_fetch (&foovar, -1);]])],
-      libgfor_cv_have_sync_fetch_and_add=yes, libgfor_cv_have_sync_fetch_and_add=no)])
-  if test $libgfor_cv_have_sync_fetch_and_add = yes; then
-    AC_DEFINE(HAVE_SYNC_FETCH_AND_ADD, 1,
-      [Define to 1 if the target supports __sync_fetch_and_add])
+if (foovar <= 0) return __atomic_fetch_add (&foovar, 1, __ATOMIC_ACQ_REL);
+if (foovar > 10) return __atomic_add_fetch (&foovar, -1, __ATOMIC_ACQ_REL);]])],
+      libgfor_cv_have_atomic_fetch_add=yes, libgfor_cv_have_atomic_fetch_add=no)])
+  if test $libgfor_cv_have_atomic_fetch_add = yes; then
+    AC_DEFINE(HAVE_ATOMIC_FETCH_ADD, 1,
+      [Define to 1 if the target supports __atomic_fetch_add])
   fi])
 
 dnl Check for pragma weak.
diff --git a/libgfortran/configure.ac b/libgfortran/configure.ac
index 76007d38f6f..30ff8734760 100644
--- a/libgfortran/configure.ac
+++ b/libgfortran/configure.ac
@@ -608,8 +608,8 @@ fi
 LIBGFOR_CHECK_ATTRIBUTE_VISIBILITY
 LIBGFOR_CHECK_ATTRIBUTE_ALIAS
 
-# Check out sync builtins support.
-LIBGFOR_CHECK_SYNC_FETCH_AND_ADD
+# Check out atomic builtins support.
+LIBGFOR_CHECK_ATOMIC_FETCH_ADD
 
 # Check out #pragma weak.
 LIBGFOR_GTHREAD_WEAK
diff --git a/libgfortran/io/io.h b/libgfortran/io/io.h
index 902eb412848..36245cbff1f 100644
--- a/libgfortran/io/io.h
+++ b/libgfortran/io/io.h
@@ -961,8 +961,8 @@ internal_proto(free_ionml);
 static inline void
 inc_waiting_locked (gfc_unit *u)
 {
-#ifdef HAVE_SYNC_FETCH_AND_ADD
-  (void) __sync_fetch_and_add (&u->waiting, 1);
+#ifdef HAVE_ATOMIC_FETCH_ADD
+  (void) __atomic_fetch_add (&u->waiting, 1, __ATOMIC_ACQ_REL);
 #else
   u->waiting++;
 #endif
@@ -971,8 +971,8 @@ inc_waiting_locked (gfc_unit *u)
 static inline int
 predec_waiting_locked (gfc_unit *u)
 {
-#ifdef HAVE_SYNC_FETCH_AND_ADD
-  return __sync_add_and_fetch (&u->waiting, -1);
+#ifdef HAVE_ATOMIC_FETCH_ADD
+  return __atomic_add_fetch (&u->waiting, -1, __ATOMIC_ACQ_REL);
 #else
   return --u->waiting;
 #endif
@@ -981,8 +981,8 @@ predec_waiting_locked (gfc_unit *u)
 static inline void
 dec_waiting_unlocked (gfc_unit *u)
 {
-#ifdef HAVE_SYNC_FETCH_AND_ADD
-  (void) __sync_fetch_and_add (&u->waiting, -1);
+#ifdef HAVE_ATOMIC_FETCH_ADD
+  (void) __atomic_fetch_add (&u->waiting, -1, __ATOMIC_ACQ_REL);
 #else
   __gthread_mutex_lock (&unit_lock);
   u->waiting--;
--
2.17.1