Avoid unexpected conversion overflow in planner for distant date values.

The "date" type supports a wider range of dates than int64 timestamps do.
However, there is pre-int64-timestamp code in the planner that assumes that
all date values can be converted to timestamp with impunity.  Fortunately,
what we really need out of the conversion is always a double (float8)
value; so even when the date is out of timestamp's range it's possible to
produce a sane answer.  All we need is a code path that doesn't try to
force the result into int64.  Per trouble report from David Rericha.

Back-patch to all supported versions.  Although this is surely a corner
case, there's not much point in advertising a date range wider than
timestamp's if we will choke on such values in unexpected places.

src/backend/utils/adt/date.c

@@ -459,6 +459,39 @@ date2timestamptz(DateADT dateVal)
 	return result;
 }
 
+/*
+ * date2timestamp_no_overflow
+ *
+ * This is chartered to produce a double value that is numerically
+ * equivalent to the corresponding Timestamp value, if the date is in the
+ * valid range of Timestamps, but in any case not throw an overflow error.
+ * We can do this since the numerical range of double is greater than
+ * that of non-erroneous timestamps.  The results are currently only
+ * used for statistical estimation purposes.
+ */
+double
+date2timestamp_no_overflow(DateADT dateVal)
+{
+	double	result;
+
+	if (DATE_IS_NOBEGIN(dateVal))
+		result = -DBL_MAX;
+	else if (DATE_IS_NOEND(dateVal))
+		result = DBL_MAX;
+	else
+	{
+#ifdef HAVE_INT64_TIMESTAMP
+		/* date is days since 2000, timestamp is microseconds since same... */
+		result = dateVal * (double) USECS_PER_DAY;
+#else
+		/* date is days since 2000, timestamp is seconds since same... */
+		result = dateVal * (double) SECS_PER_DAY;
+#endif
+	}
+
+	return result;
+}
+
 
 /*
  * Crosstype comparison functions for dates

src/backend/utils/adt/selfuncs.c

@@ -3865,8 +3865,7 @@ convert_timevalue_to_scalar(Datum value, Oid typid)
 			return DatumGetTimestamp(DirectFunctionCall1(abstime_timestamp,
 														 value));
 		case DATEOID:
-			return DatumGetTimestamp(DirectFunctionCall1(date_timestamp,
-														 value));
+			return date2timestamp_no_overflow(DatumGetDateADT(value));
 		case INTERVALOID:
 			{
 				Interval   *interval = DatumGetIntervalP(value);

src/include/utils/date.h

@@ -91,6 +91,8 @@ typedef struct
 
 
 /* date.c */
+extern double date2timestamp_no_overflow(DateADT dateVal);
+
 extern Datum date_in(PG_FUNCTION_ARGS);
 extern Datum date_out(PG_FUNCTION_ARGS);
 extern Datum date_recv(PG_FUNCTION_ARGS);