Work toward reducing the incremental size of an ExprList object to 24-byte

per entry, from 32-bytes (on a 64-bit machine).  This helps the new
mini-lookaside allocator to run better by avoiding excessive reallocs.
The current change mostly works, but still has a few loose ends to tie up.
This check-in is merely a snapshot to save my work.

FossilOrigin-Name: fdda76cfb01bf2b19522ac4558b443634d28a69b0828677c42682b645eae1f3b

6 files changed, 54 insertions, 39 deletions

diff --git a/manifest b/manifest
index 5f8fb620c..e886d85f4 100644
--- a/manifest
+++ b/manifest
@@ -1,5 +1,5 @@
-C Fix\san\sissue\swhere\smalloc\scould\sbe\sused\sto\sfulfill\sa\ssmall\sallocation\swhen\sa\slarge\slookaside\sslot\scould\shave\sbeeen\sused\sinstead.
-D 2019-12-12T20:39:47.705
+C Work\stoward\sreducing\sthe\sincremental\ssize\sof\san\sExprList\sobject\sto\s24-byte\nper\sentry,\sfrom\s32-bytes\s(on\sa\s64-bit\smachine).\s\sThis\shelps\sthe\snew\nmini-lookaside\sallocator\sto\srun\sbetter\sby\savoiding\sexcessive\sreallocs.\nThe\scurrent\schange\smostly\sworks,\sbut\sstill\shas\sa\sfew\sloose\sends\sto\stie\sup.\nThis\scheck-in\sis\smerely\sa\ssnapshot\sto\ssave\smy\swork.
+D 2019-12-12T22:11:33.445
 F .fossil-settings/empty-dirs dbb81e8fc0401ac46a1491ab34a7f2c7c0452f2f06b54ebb845d024ca8283ef1
 F .fossil-settings/ignore-glob 35175cdfcf539b2318cb04a9901442804be81cd677d8b889fcc9149c21f239ea
 F LICENSE.md df5091916dbb40e6e9686186587125e1b2ff51f022cc334e886c19a0e9982724
@@ -479,7 +479,7 @@ F src/date.c e1d8ac7102f3f283e63e13867acb0efa33861cf34f0faf4cdbaf9fa7a1eb7041
 F src/dbpage.c 135eb3b5e74f9ef74bde5cec2571192c90c86984fa534c88bf4a055076fa19b7
 F src/dbstat.c 6c407e549406c10fde9ac3987f6d734459205239ad370369bc5fcd683084a4fa
 F src/delete.c a5c59b9c0251cf7682bc52af0d64f09b1aefc6781a63592c8f1136f7b73c66e4
-F src/expr.c eefc9abca2d8bb8b2cad063dd65c764e5264f1d80c83268a9debcfff2f7a32bb
+F src/expr.c 828bc6ae0c15e60a5b0a5fb17ddf98fb3f9a52752fb34cbbdc15ea4868afcf90
 F src/fault.c 460f3e55994363812d9d60844b2a6de88826e007
 F src/fkey.c 92a248ec0fa4ed8ab60c98d9b188ce173aaf218f32e7737ba77deb2a684f9847
 F src/func.c ed33e38cd642058182a31a3f518f2e34f4bbe53aa483335705c153c4d3e50b12
@@ -525,14 +525,14 @@ F src/pragma.h ec3b31eac9b1df040f1cc8cb3d89bc06605c3b4cb3d76f833de8d6d6c3f77f04
 F src/prepare.c 6049beb71385f017af6fc320d2c75a4e50b75e280c54232442b785fbb83df057
 F src/printf.c 9be6945837c839ba57837b4bc3af349eba630920fa5532aa518816defe42a7d4
 F src/random.c 80f5d666f23feb3e6665a6ce04c7197212a88384
-F src/resolve.c d703803412770e100be0d79adc4d0b52a99c49715ba8d4a736e503ee5526d473
+F src/resolve.c fc7bed8f23355db3af73859b4af42af4ee2f7cf3467aa5e242321575203e2896
 F src/rowset.c d977b011993aaea002cab3e0bb2ce50cf346000dff94e944d547b989f4b1fe93
-F src/select.c 39a9e180a2fdf738f3a02977684bc4cad3f5ff8d9f949f2aa48eef2ce5ff29aa
+F src/select.c b5702ca6b2f215bb8bee27f591d72dfd52250a680b5fa11871a1a7be69dff758
 F src/shell.c.in 4a3a9e1c11847b1904f2b01d087af1c052f660902755abab457cab1756817ded
 F src/sqlite.h.in 2a23e8161775253d9cf383c2c6aa559005dc787d350dcb0be67a6c4cc3bd1d19
 F src/sqlite3.rc 5121c9e10c3964d5755191c80dd1180c122fc3a8
 F src/sqlite3ext.h 72af51aa4e912e14cd495fb6e7fac65f0940db80ed950d90911aff292cc47ce2
-F src/sqliteInt.h ebb8c7e6439dc4cd6abad9fed0d01751160115328c8670b733505d7c5c6b12a4
+F src/sqliteInt.h 5be56f6523e0980b4ab66d6420e11dbe66c060c7b2e20aa28344fd67457cbe32
 F src/sqliteLimit.h 1513bfb7b20378aa0041e7022d04acb73525de35b80b252f1b83fedb4de6a76b
 F src/status.c 0fe55b92810509eac821ded2e177e1da944a78cdcdfec7813ad1d6b36d6d667e
 F src/table.c b46ad567748f24a326d9de40e5b9659f96ffff34
@@ -1852,7 +1852,10 @@ F vsixtest/vsixtest.tcl 6a9a6ab600c25a91a7acc6293828957a386a8a93
 F vsixtest/vsixtest.vcxproj.data 2ed517e100c66dc455b492e1a33350c1b20fbcdc
 F vsixtest/vsixtest.vcxproj.filters 37e51ffedcdb064aad6ff33b6148725226cd608e
 F vsixtest/vsixtest_TemporaryKey.pfx e5b1b036facdb453873e7084e1cae9102ccc67a0
-P d3783357f8fa76c42a86f12b214522f0388c37773c36ab8c5ce0623abbc4436a
-R 419a6defa175975b0c1f1ba26db0be60
-U numist
-Z c7e98609c62b97e8952867680421d71f
+P 611020e3378f4c81c277cccd84807ae51a816bbab6c3d887c91c5e5af3b5225f
+R 162199bc809f1616aa82013813cc7e3c
+T *branch * exprlist-size-reduction
+T *sym-exprlist-size-reduction *
+T -sym-mini-lookaside-take-2 *
+U drh
+Z 2404f597cd0a4292958003b4ec4cbb04
diff --git a/manifest.uuid b/manifest.uuid
index 50a02db88..fe20ecead 100644
--- a/manifest.uuid
+++ b/manifest.uuid
@@ -1 +1 @@
-611020e3378f4c81c277cccd84807ae51a816bbab6c3d887c91c5e5af3b5225f
\ No newline at end of file
+fdda76cfb01bf2b19522ac4558b443634d28a69b0828677c42682b645eae1f3b
\ No newline at end of file
diff --git a/src/expr.c b/src/expr.c
index f9c57baa9..0ca1d0407 100644
--- a/src/expr.c
+++ b/src/expr.c
@@ -1437,11 +1437,10 @@ ExprList *sqlite3ExprListDup(sqlite3 *db, ExprList *p, int flags){
       }
     }
     pItem->zEName = sqlite3DbStrDup(db, pOldItem->zEName);
-    pItem->zSpan = sqlite3DbStrDup(db, pOldItem->zSpan);
     pItem->sortFlags = pOldItem->sortFlags;
+    pItem->eEName = pOldItem->eEName;
     pItem->done = 0;
     pItem->bNulls = pOldItem->bNulls;
-    pItem->bSpanIsTab = pOldItem->bSpanIsTab;
     pItem->bSorterRef = pOldItem->bSorterRef;
     pItem->u = pOldItem->u;
   }
@@ -1773,8 +1772,10 @@ void sqlite3ExprListSetSpan(
   if( pList ){
     struct ExprList_item *pItem = &pList->a[pList->nExpr-1];
     assert( pList->nExpr>0 );
-    sqlite3DbFree(db, pItem->zSpan);
-    pItem->zSpan = sqlite3DbSpanDup(db, zStart, zEnd);
+    if( pItem->zEName==0 ){
+      pItem->zEName = sqlite3DbSpanDup(db, zStart, zEnd);
+      pItem->eEName = ENAME_SPAN;
+    }
   }
 }
 
@@ -1805,7 +1806,6 @@ static SQLITE_NOINLINE void exprListDeleteNN(sqlite3 *db, ExprList *pList){
   do{
     sqlite3ExprDelete(db, pItem->pExpr);
     sqlite3DbFree(db, pItem->zEName);
-    sqlite3DbFree(db, pItem->zSpan);
     pItem++;
   }while( --i>0 );
   sqlite3DbFreeNN(db, pList);
diff --git a/src/resolve.c b/src/resolve.c
index b3c331535..cce921031 100644
--- a/src/resolve.c
+++ b/src/resolve.c
@@ -267,7 +267,7 @@ static int lookupName(
           int hit = 0;
           pEList = pItem->pSelect->pEList;
           for(j=0; j<pEList->nExpr; j++){
-            if( sqlite3MatchSpanName(pEList->a[j].zSpan, zCol, zTab, zDb) ){
+            if( sqlite3MatchSpanName(pEList->a[j].zEName, zCol, zTab, zDb) ){
               cnt++;
               cntTab = 2;
               pMatch = pItem;
diff --git a/src/select.c b/src/select.c
index b99b1459b..57bf685ed 100644
--- a/src/select.c
+++ b/src/select.c
@@ -1539,7 +1539,7 @@ static void generateSortTail(
         iRead = iCol--;
       }
       sqlite3VdbeAddOp3(v, OP_Column, iSortTab, iRead, regRow+i);
-      VdbeComment((v, "%s", aOutEx[i].zEName?aOutEx[i].zEName:aOutEx[i].zSpan));
+      VdbeComment((v, "%s", aOutEx[i].zEName));
     }
   }
   switch( eDest ){
@@ -1873,7 +1873,7 @@ static void generateColumnNames(
     assert( p!=0 );
     assert( p->op!=TK_AGG_COLUMN );  /* Agg processing has not run yet */
     assert( p->op!=TK_COLUMN || p->y.pTab!=0 ); /* Covering idx not yet coded */
-    if( pEList->a[i].zEName ){
+    if( pEList->a[i].zEName && pEList->a[i].eEName==ENAME_NAME ){
       /* An AS clause always takes first priority */
       char *zName = pEList->a[i].zEName;
       sqlite3VdbeSetColName(v, i, COLNAME_NAME, zName, SQLITE_TRANSIENT);
@@ -1897,7 +1897,7 @@ static void generateColumnNames(
         sqlite3VdbeSetColName(v, i, COLNAME_NAME, zCol, SQLITE_TRANSIENT);
       }
     }else{
-      const char *z = pEList->a[i].zSpan;
+      const char *z = pEList->a[i].zEName;
       z = z==0 ? sqlite3MPrintf(db, "column%d", i+1) : sqlite3DbStrDup(db, z);
       sqlite3VdbeSetColName(v, i, COLNAME_NAME, z, SQLITE_DYNAMIC);
     }
@@ -1959,7 +1959,7 @@ int sqlite3ColumnsFromExprList(
   for(i=0, pCol=aCol; i<nCol && !db->mallocFailed; i++, pCol++){
     /* Get an appropriate name for the column
     */
-    if( (zName = pEList->a[i].zEName)!=0 ){
+    if( (zName = pEList->a[i].zEName)!=0 && pEList->a[i].eEName==ENAME_NAME ){
       /* If the column contains an "AS <name>" phrase, use <name> as the name */
     }else{
       Expr *pColExpr = sqlite3ExprSkipCollateAndLikely(pEList->a[i].pExpr);
@@ -1979,7 +1979,7 @@ int sqlite3ColumnsFromExprList(
         zName = pColExpr->u.zToken;
       }else{
         /* Use the original text of the column expression as its name */
-        zName = pEList->a[i].zSpan;
+        zName = pEList->a[i].zEName;
       }
     }
     if( zName ){
@@ -5004,9 +5004,8 @@ static int selectExpander(Walker *pWalker, Select *p){
         pNew = sqlite3ExprListAppend(pParse, pNew, a[k].pExpr);
         if( pNew ){
           pNew->a[pNew->nExpr-1].zEName = a[k].zEName;
-          pNew->a[pNew->nExpr-1].zSpan = a[k].zSpan;
+          pNew->a[pNew->nExpr-1].eEName = a[k].eEName;
           a[k].zEName = 0;
-          a[k].zSpan = 0;
         }
         a[k].pExpr = 0;
       }else{
@@ -5045,7 +5044,7 @@ static int selectExpander(Walker *pWalker, Select *p){
 
             assert( zName );
             if( zTName && pSub
-             && sqlite3MatchSpanName(pSub->pEList->a[j].zSpan, 0, zTName, 0)==0
+             && sqlite3MatchSpanName(pSub->pEList->a[j].zEName, 0, zTName, 0)==0
             ){
               continue;
             }
@@ -5098,15 +5097,16 @@ static int selectExpander(Walker *pWalker, Select *p){
             sqlite3ExprListSetName(pParse, pNew, &sColname, 0);
             if( pNew && (p->selFlags & SF_NestedFrom)!=0 ){
               struct ExprList_item *pX = &pNew->a[pNew->nExpr-1];
+              sqlite3DbFree(db, pX->zEName);
               if( pSub ){
-                pX->zSpan = sqlite3DbStrDup(db, pSub->pEList->a[j].zSpan);
-                testcase( pX->zSpan==0 );
+                pX->zEName = sqlite3DbStrDup(db, pSub->pEList->a[j].zEName);
+                testcase( pX->zEName==0 );
               }else{
-                pX->zSpan = sqlite3MPrintf(db, "%s.%s.%s",
+                pX->zEName = sqlite3MPrintf(db, "%s.%s.%s",
                                            zSchemaName, zTabName, zColname);
-                testcase( pX->zSpan==0 );
+                testcase( pX->zEName==0 );
               }
-              pX->bSpanIsTab = 1;
+              pX->eEName = ENAME_TAB;
             }
             sqlite3DbFree(db, zToFree);
           }
diff --git a/src/sqliteInt.h b/src/sqliteInt.h
index 3de659f79..7425b2988 100644
--- a/src/sqliteInt.h
+++ b/src/sqliteInt.h
@@ -2650,23 +2650,28 @@ struct Expr {
 ** also be used as the argument to a function, in which case the a.zName
 ** field is not used.
 **
-** By default the Expr.zSpan field holds a human-readable description of
-** the expression that is used in the generation of error messages and
-** column labels.  In this case, Expr.zSpan is typically the text of a
-** column expression as it exists in a SELECT statement.  However, if
-** the bSpanIsTab flag is set, then zSpan is overloaded to mean the name
-** of the result column in the form: DATABASE.TABLE.COLUMN.  This later
-** form is used for name resolution with nested FROM clauses.
+** In order to try to keep memory usage down, the Expr.a.zEName field
+** is used for multiple purposes:
+**
+**     bNameIsTab    bNameIsSpan        Usage
+**     ----------    -----------        -------------------------
+**       false          false           (1) the AS of result set column
+**                                      (2) COLUMN= of an UPDATE
+**
+**       true           false           DB.TABLE.NAME used to resolve names
+**                                      of subqueries
+**
+**       false          true            Text of the original result set
+**                                      expression.
 */
 struct ExprList {
   int nExpr;             /* Number of expressions on the list */
   struct ExprList_item { /* For each expression in the list */
     Expr *pExpr;            /* The parse tree for this expression */
     char *zEName;           /* Token associated with this expression */
-    char *zSpan;            /* Original text of the expression */
     u8 sortFlags;           /* Mask of KEYINFO_ORDER_* flags */
+    unsigned eEName :2;     /* Meaning of zEName */
     unsigned done :1;       /* A flag to indicate when processing is finished */
-    unsigned bSpanIsTab :1; /* zSpan holds DB.TABLE.COLUMN */
     unsigned reusable :1;   /* Constant expression is reusable */
     unsigned bSorterRef :1; /* Defer evaluation until after sorting */
     unsigned bNulls: 1;     /* True if explicit "NULLS FIRST/LAST" */
@@ -2681,6 +2686,13 @@ struct ExprList {
 };
 
 /*
+** Allowed values for Expr.a.eEName
+*/
+#define ENAME_NAME  0       /* The AS clause of a result set */
+#define ENAME_SPAN  1       /* Complete text of the result set expression */
+#define ENAME_TAB   2       /* "DB.TABLE.NAME" for the result set */
+
+/*
 ** An instance of this structure can hold a simple list of identifiers,
 ** such as the list "a,b,c" in the following statements:
 **