3 files changed, 19 insertions, 8 deletions
diff --git a/src/include/c.h b/src/include/c.h
index 802a731267f..00e41ac546a 100644
--- a/src/include/c.h
+++ b/src/include/c.h
@@ -491,6 +491,12 @@ typedef signed int Offset;
 typedef float float4;
 typedef double float8;
 
+#ifdef USE_FLOAT8_BYVAL
+#define FLOAT8PASSBYVAL true
+#else
+#define FLOAT8PASSBYVAL false
+#endif
+
 /*
  * Oid, RegProcedure, TransactionId, SubTransactionId, MultiXactId,
  * CommandId
diff --git a/src/include/pg_config.h.in b/src/include/pg_config.h.in
index 6f8549bc03b..c208dcdfc71 100644
--- a/src/include/pg_config.h.in
+++ b/src/include/pg_config.h.in
@@ -70,10 +70,6 @@
    MSVC and with C++ compilers. */
 #undef FLEXIBLE_ARRAY_MEMBER
 
-/* float8, int8, and related values are passed by value if 'true', by
-   reference if 'false' */
-#undef FLOAT8PASSBYVAL
-
 /* Define to 1 if gettimeofday() takes only 1 argument. */
 #undef GETTIMEOFDAY_1ARG
 
@@ -898,10 +894,6 @@
 /* Define to use /dev/urandom for random number generation */
 #undef USE_DEV_URANDOM
 
-/* Define to 1 if you want float8, int8, etc values to be passed by value.
-   (--enable-float8-byval) */
-#undef USE_FLOAT8_BYVAL
-
 /* Define to build with ICU support. (--with-icu) */
 #undef USE_ICU
 
diff --git a/src/include/pg_config_manual.h b/src/include/pg_config_manual.h
index 743401cb969..61b667d1663 100644
--- a/src/include/pg_config_manual.h
+++ b/src/include/pg_config_manual.h
@@ -57,6 +57,19 @@
 #define PARTITION_MAX_KEYS	32
 
 /*
+ * Decide whether built-in 8-byte types, including float8, int8, and
+ * timestamp, are passed by value.  This is on by default if sizeof(Datum) >=
+ * 8 (that is, on 64-bit platforms).  If sizeof(Datum) < 8 (32-bit platforms),
+ * this must be off.  We keep this here as an option so that it is easy to
+ * test the pass-by-reference code paths on 64-bit platforms.
+ *
+ * Changing this requires an initdb.
+ */
+#if SIZEOF_VOID_P >= 8
+#define USE_FLOAT8_BYVAL 1
+#endif
+
+/*
  * When we don't have native spinlocks, we use semaphores to simulate them.
  * Decreasing this value reduces consumption of OS resources; increasing it
  * may improve performance, but supplying a real spinlock implementation is