Fix issues in e8fdbd58fe.

When the 64bit atomics simulation is in use, we can't necessarily
guarantee the correct alignment of the atomics due to lack of compiler
support for doing so- that's fine from a safety perspective, because
everything is protected by a lock, but we asserted the alignment in
all cases.  Weaken them.  Per complaint from Alvaro Herrera.

My #ifdefery for PG_HAVE_8BYTE_SINGLE_COPY_ATOMICITY wasn't
sufficient. Fix that.  Per complaint from Alexander Korotkov.

1 files changed, 35 insertions, 14 deletions

diff --git a/src/include/port/atomics/generic.h b/src/include/port/atomics/generic.h
index c0942482fc5..424543604ab 100644
--- a/src/include/port/atomics/generic.h
+++ b/src/include/port/atomics/generic.h
@@ -271,26 +271,26 @@ pg_atomic_exchange_u64_impl(volatile pg_atomic_uint64 *ptr, uint64 xchg_)
 }
 #endif
 
-#ifndef PG_HAVE_ATOMIC_READ_U64
-#define PG_HAVE_ATOMIC_READ_U64
-static inline uint64
-pg_atomic_read_u64_impl(volatile pg_atomic_uint64 *ptr)
-{
-	return *(&ptr->value);
-}
-#endif
-
 #ifndef PG_HAVE_ATOMIC_WRITE_U64
 #define PG_HAVE_ATOMIC_WRITE_U64
+
+#if defined(PG_HAVE_8BYTE_SINGLE_COPY_ATOMICITY) && \
+	!defined(PG_HAVE_ATOMIC_U64_SIMULATION)
+
 static inline void
 pg_atomic_write_u64_impl(volatile pg_atomic_uint64 *ptr, uint64 val)
 {
+	/*
+	 * On this platform aligned 64bit writes are guaranteed to be atomic,
+	 * except if using the fallback implementation, where can't guarantee the
+	 * required alignment.
+	 */
+	AssertPointerAlignment(ptr, 8);
 	ptr->value = val;
 }
-#endif
 
-#ifndef PG_HAVE_ATOMIC_WRITE_U64
-#define PG_HAVE_ATOMIC_WRITE_U64
+#else
+
 static inline void
 pg_atomic_write_u64_impl(volatile pg_atomic_uint64 *ptr, uint64 val)
 {
@@ -300,10 +300,30 @@ pg_atomic_write_u64_impl(volatile pg_atomic_uint64 *ptr, uint64 val)
 	 */
 	pg_atomic_exchange_u64_impl(ptr, val);
 }
-#endif
+
+#endif /* PG_HAVE_8BYTE_SINGLE_COPY_ATOMICITY && !PG_HAVE_ATOMIC_U64_SIMULATION */
+#endif /* PG_HAVE_ATOMIC_WRITE_U64 */
 
 #ifndef PG_HAVE_ATOMIC_READ_U64
 #define PG_HAVE_ATOMIC_READ_U64
+
+#if defined(PG_HAVE_8BYTE_SINGLE_COPY_ATOMICITY) && \
+	!defined(PG_HAVE_ATOMIC_U64_SIMULATION)
+
+static inline uint64
+pg_atomic_read_u64_impl(volatile pg_atomic_uint64 *ptr)
+{
+	/*
+	 * On this platform aligned 64bit reads are guaranteed to be atomic,
+	 * except if using the fallback implementation, where can't guarantee the
+	 * required alignment.
+	 */
+	AssertPointerAlignment(ptr, 8);
+	return *(&ptr->value);
+}
+
+#else
+
 static inline uint64
 pg_atomic_read_u64_impl(volatile pg_atomic_uint64 *ptr)
 {
@@ -319,7 +339,8 @@ pg_atomic_read_u64_impl(volatile pg_atomic_uint64 *ptr)
 
 	return old;
 }
-#endif
+#endif /* PG_HAVE_8BYTE_SINGLE_COPY_ATOMICITY && !PG_HAVE_ATOMIC_U64_SIMULATION */
+#endif /* PG_HAVE_ATOMIC_READ_U64 */
 
 #ifndef PG_HAVE_ATOMIC_INIT_U64
 #define PG_HAVE_ATOMIC_INIT_U64