Add the ability to factor constant functions out of inner loops.  But do
not factor out non-constant functions, like random().

FossilOrigin-Name: 1b0f779e19a5c0d51eddd2d88db50034d77d132c
diff --git a/src/sqliteInt.h b/src/sqliteInt.h
index f52c6c1..84c6997 100644
--- a/src/sqliteInt.h
+++ b/src/sqliteInt.h
@@ -1143,6 +1143,7 @@
 #define SQLITE_FUNC_COUNT    0x100 /* Built-in count(*) aggregate */
 #define SQLITE_FUNC_COALESCE 0x200 /* Built-in coalesce() or ifnull() */
 #define SQLITE_FUNC_UNLIKELY 0x400 /* Built-in unlikely() function */
+#define SQLITE_FUNC_CONSTANT 0x800 /* Constant inputs give a constant output */
 
 /*
 ** The following three macros, FUNCTION(), LIKEFUNC() and AGGREGATE() are
@@ -1155,6 +1156,9 @@
 **     as the user-data (sqlite3_user_data()) for the function. If 
 **     argument bNC is true, then the SQLITE_FUNC_NEEDCOLL flag is set.
 **
+**   VFUNCTION(zName, nArg, iArg, bNC, xFunc)
+**     Like FUNCTION except it omits the SQLITE_FUNC_CONSTANT flag.
+**
 **   AGGREGATE(zName, nArg, iArg, bNC, xStep, xFinal)
 **     Used to create an aggregate function definition implemented by
 **     the C functions xStep and xFinal. The first four parameters
@@ -1170,16 +1174,20 @@
 **     parameter.
 */
 #define FUNCTION(zName, nArg, iArg, bNC, xFunc) \
+  {nArg, SQLITE_FUNC_CONSTANT|SQLITE_UTF8|(bNC*SQLITE_FUNC_NEEDCOLL), \
+   SQLITE_INT_TO_PTR(iArg), 0, xFunc, 0, 0, #zName, 0, 0}
+#define VFUNCTION(zName, nArg, iArg, bNC, xFunc) \
   {nArg, SQLITE_UTF8|(bNC*SQLITE_FUNC_NEEDCOLL), \
    SQLITE_INT_TO_PTR(iArg), 0, xFunc, 0, 0, #zName, 0, 0}
 #define FUNCTION2(zName, nArg, iArg, bNC, xFunc, extraFlags) \
-  {nArg, SQLITE_UTF8|(bNC*SQLITE_FUNC_NEEDCOLL)|extraFlags, \
+  {nArg,SQLITE_FUNC_CONSTANT|SQLITE_UTF8|(bNC*SQLITE_FUNC_NEEDCOLL)|extraFlags,\
    SQLITE_INT_TO_PTR(iArg), 0, xFunc, 0, 0, #zName, 0, 0}
 #define STR_FUNCTION(zName, nArg, pArg, bNC, xFunc) \
-  {nArg, SQLITE_UTF8|(bNC*SQLITE_FUNC_NEEDCOLL), \
+  {nArg, SQLITE_FUNC_CONSTANT|SQLITE_UTF8|(bNC*SQLITE_FUNC_NEEDCOLL), \
    pArg, 0, xFunc, 0, 0, #zName, 0, 0}
 #define LIKEFUNC(zName, nArg, arg, flags) \
-  {nArg, SQLITE_UTF8|flags, (void *)arg, 0, likeFunc, 0, 0, #zName, 0, 0}
+  {nArg, SQLITE_FUNC_CONSTANT|SQLITE_UTF8|flags, \
+   (void *)arg, 0, likeFunc, 0, 0, #zName, 0, 0}
 #define AGGREGATE(zName, nArg, arg, nc, xStep, xFinal) \
   {nArg, SQLITE_UTF8|(nc*SQLITE_FUNC_NEEDCOLL), \
    SQLITE_INT_TO_PTR(arg), 0, 0, xStep,xFinal,#zName,0,0}
@@ -1839,6 +1847,7 @@
 #define EP_MemToken  0x010000 /* Need to sqlite3DbFree() Expr.zToken */
 #define EP_NoReduce  0x020000 /* Cannot EXPRDUP_REDUCE this Expr */
 #define EP_Unlikely  0x040000 /* unlikely() or likelihood() function */
+#define EP_Constant  0x080000 /* Node is a constant */
 
 /*
 ** These macros can be used to test, set, or clear bits in the