Use the VList object to replace Parse.azVar for tracking the mapping between

SQL parameter names and parameter numbers.  There is a performance
improvement, though there are still a few hiccups in the current code.

FossilOrigin-Name: 68ecafa1425a41358c88f41efea3262f1b4490f2

src/sqliteInt.h

@@ -1046,6 +1046,14 @@ typedef struct Walker Walker;
 typedef struct WhereInfo WhereInfo;
 typedef struct With With;
 
+/* A VList object records a mapping between parameters/variables/wildcards
+** in the SQL statement (such as $abc, @pqr, or :xyz) and the integer
+** variable number associated with that parameter.  See the format description
+** on the sqlite3VListAdd() routine for more information.  A VList is really
+** just an array of integers.
+*/
+typedef int VList;
+
 /*
 ** Defer sourcing vdbe.h and btree.h until after the "u8" and
 ** "BusyHandler" typedefs. vdbe.h also requires a few of the opaque
@@ -2952,7 +2960,6 @@ struct Parse {
 
   Token sLastToken;       /* The last token parsed */
   ynVar nVar;               /* Number of '?' variables seen in the SQL so far */
-  int nzVar;                /* Number of available slots in azVar[] */
   u8 iPkSortOrder;          /* ASC or DESC for INTEGER PRIMARY KEY */
   u8 explain;               /* True if the EXPLAIN flag is found on the query */
 #ifndef SQLITE_OMIT_VIRTUALTABLE
@@ -2964,7 +2971,7 @@ struct Parse {
   int iSelectId;            /* ID of current select for EXPLAIN output */
   int iNextSelectId;        /* Next available select ID for EXPLAIN output */
 #endif
-  char **azVar;             /* Pointers to names of parameters */
+  VList *pVList;            /* Mapping between variable names and numbers */
   Vdbe *pReprepare;         /* VM being reprepared (sqlite3Reprepare()) */
   const char *zTail;        /* All SQL text past the last semicolon parsed */
   Table *pNewTable;         /* A table being constructed by CREATE TABLE */
@@ -3864,6 +3871,9 @@ LogEst sqlite3LogEstFromDouble(double);
     defined(SQLITE_EXPLAIN_ESTIMATED_ROWS)
 u64 sqlite3LogEstToInt(LogEst);
 #endif
+VList *sqlite3VListAdd(sqlite3*,VList*,const char*,int,int);
+const char *sqlite3VListNumToName(VList*,int);
+int sqlite3VListNameToNum(VList*,const char*,int);
 
 /*
 ** Routines to read and write variable-length integers.  These used to