Add the new internal interface sqlite3DbNNFreeNN(db,ptr) where both the

db and ptr parameters are guaranteed to be non-NULL.  Use this where
appropriate to save more than 2 million CPU cycles on the standard
performance test.

FossilOrigin-Name: e5eaa80e81fdf86f2875a912b880272b8d099b82b08e945a7988c5dd0fe9d6b5

16 files changed, 106 insertions, 46 deletions

diff --git a/src/btmutex.c b/src/btmutex.c
index 275a93ff2..45745b001 100644
--- a/src/btmutex.c
+++ b/src/btmutex.c
@@ -252,6 +252,7 @@ int sqlite3BtreeHoldsAllMutexes(sqlite3 *db){
 int sqlite3SchemaMutexHeld(sqlite3 *db, int iDb, Schema *pSchema){
   Btree *p;
   assert( db!=0 );
+  if( db->pVfs==0 && db->nDb==0 ) return 1;
   if( pSchema ) iDb = sqlite3SchemaToIndex(db, pSchema);
   assert( iDb>=0 && iDb<db->nDb );
   if( !sqlite3_mutex_held(db->mutex) ) return 0;
diff --git a/src/build.c b/src/build.c
index e3e79df05..094cf7d61 100644
--- a/src/build.c
+++ b/src/build.c
@@ -775,16 +775,17 @@ void sqlite3DeleteColumnNames(sqlite3 *db, Table *pTable){
   int i;
   Column *pCol;
   assert( pTable!=0 );
+  assert( db!=0 );
   if( (pCol = pTable->aCol)!=0 ){
     for(i=0; i<pTable->nCol; i++, pCol++){
       assert( pCol->zCnName==0 || pCol->hName==sqlite3StrIHash(pCol->zCnName) );
       sqlite3DbFree(db, pCol->zCnName);
     }
-    sqlite3DbFree(db, pTable->aCol);
+    sqlite3DbNNFreeNN(db, pTable->aCol);
     if( IsOrdinaryTable(pTable) ){
       sqlite3ExprListDelete(db, pTable->u.tab.pDfltList);
     }
-    if( db==0 || db->pnBytesFreed==0 ){
+    if( db->pnBytesFreed==0 ){
       pTable->aCol = 0;
       pTable->nCol = 0;
       if( IsOrdinaryTable(pTable) ){
@@ -821,7 +822,8 @@ static void SQLITE_NOINLINE deleteTable(sqlite3 *db, Table *pTable){
   ** a Table object that was going to be marked ephemeral. So do not check
   ** that no lookaside memory is used in this case either. */
   int nLookaside = 0;
-  if( db && !db->mallocFailed && (pTable->tabFlags & TF_Ephemeral)==0 ){
+  assert( db!=0 );
+  if( !db->mallocFailed && (pTable->tabFlags & TF_Ephemeral)==0 ){
     nLookaside = sqlite3LookasideUsed(db, 0);
   }
 #endif
@@ -831,7 +833,7 @@ static void SQLITE_NOINLINE deleteTable(sqlite3 *db, Table *pTable){
     pNext = pIndex->pNext;
     assert( pIndex->pSchema==pTable->pSchema
          || (IsVirtual(pTable) && pIndex->idxType!=SQLITE_IDXTYPE_APPDEF) );
-    if( (db==0 || db->pnBytesFreed==0) && !IsVirtual(pTable) ){
+    if( db->pnBytesFreed==0 && !IsVirtual(pTable) ){
       char *zName = pIndex->zName; 
       TESTONLY ( Index *pOld = ) sqlite3HashInsert(
          &pIndex->pSchema->idxHash, zName, 0
@@ -868,8 +870,9 @@ static void SQLITE_NOINLINE deleteTable(sqlite3 *db, Table *pTable){
 }
 void sqlite3DeleteTable(sqlite3 *db, Table *pTable){
   /* Do not delete the table until the reference count reaches zero. */
+  assert( db!=0 );
   if( !pTable ) return;
-  if( ((!db || db->pnBytesFreed==0) && (--pTable->nTabRef)>0) ) return;
+  if( db->pnBytesFreed==0 && (--pTable->nTabRef)>0 ) return;
   deleteTable(db, pTable);
 }
 
@@ -4689,12 +4692,13 @@ IdList *sqlite3IdListAppend(Parse *pParse, IdList *pList, Token *pToken){
 */
 void sqlite3IdListDelete(sqlite3 *db, IdList *pList){
   int i;
+  assert( db!=0 );
   if( pList==0 ) return;
   assert( pList->eU4!=EU4_EXPR ); /* EU4_EXPR mode is not currently used */
   for(i=0; i<pList->nId; i++){
     sqlite3DbFree(db, pList->a[i].zName);
   }
-  sqlite3DbFreeNN(db, pList);
+  sqlite3DbNNFreeNN(db, pList);
 }
 
 /*
@@ -4897,11 +4901,12 @@ void sqlite3SrcListAssignCursors(Parse *pParse, SrcList *pList){
 void sqlite3SrcListDelete(sqlite3 *db, SrcList *pList){
   int i;
   SrcItem *pItem;
+  assert( db!=0 );
   if( pList==0 ) return;
   for(pItem=pList->a, i=0; i<pList->nSrc; i++, pItem++){
-    if( pItem->zDatabase ) sqlite3DbFreeNN(db, pItem->zDatabase);
-    sqlite3DbFree(db, pItem->zName);
-    if( pItem->zAlias ) sqlite3DbFreeNN(db, pItem->zAlias);
+    if( pItem->zDatabase ) sqlite3DbNNFreeNN(db, pItem->zDatabase);
+    if( pItem->zName ) sqlite3DbNNFreeNN(db, pItem->zName);
+    if( pItem->zAlias ) sqlite3DbNNFreeNN(db, pItem->zAlias);
     if( pItem->fg.isIndexedBy ) sqlite3DbFree(db, pItem->u1.zIndexedBy);
     if( pItem->fg.isTabFunc ) sqlite3ExprListDelete(db, pItem->u1.pFuncArg);
     sqlite3DeleteTable(db, pItem->pTab);
@@ -4912,7 +4917,7 @@ void sqlite3SrcListDelete(sqlite3 *db, SrcList *pList){
       sqlite3ExprDelete(db, pItem->u3.pOn);
     }
   }
-  sqlite3DbFreeNN(db, pList);
+  sqlite3DbNNFreeNN(db, pList);
 }
 
 /*
diff --git a/src/callback.c b/src/callback.c
index 7d8f9dcbc..6cbe8e584 100644
--- a/src/callback.c
+++ b/src/callback.c
@@ -490,19 +490,21 @@ void sqlite3SchemaClear(void *p){
   Hash temp2;
   HashElem *pElem;
   Schema *pSchema = (Schema *)p;
+  sqlite3 xdb;
 
+  memset(&xdb, 0, sizeof(xdb));
   temp1 = pSchema->tblHash;
   temp2 = pSchema->trigHash;
   sqlite3HashInit(&pSchema->trigHash);
   sqlite3HashClear(&pSchema->idxHash);
   for(pElem=sqliteHashFirst(&temp2); pElem; pElem=sqliteHashNext(pElem)){
-    sqlite3DeleteTrigger(0, (Trigger*)sqliteHashData(pElem));
+    sqlite3DeleteTrigger(&xdb, (Trigger*)sqliteHashData(pElem));
   }
   sqlite3HashClear(&temp2);
   sqlite3HashInit(&pSchema->tblHash);
   for(pElem=sqliteHashFirst(&temp1); pElem; pElem=sqliteHashNext(pElem)){
     Table *pTab = sqliteHashData(pElem);
-    sqlite3DeleteTable(0, pTab);
+    sqlite3DeleteTable(&xdb, pTab);
   }
   sqlite3HashClear(&temp1);
   sqlite3HashClear(&pSchema->fkeyHash);
diff --git a/src/delete.c b/src/delete.c
index 056d6f3be..704a3c711 100644
--- a/src/delete.c
+++ b/src/delete.c
@@ -676,7 +676,7 @@ delete_from_cleanup:
   sqlite3ExprListDelete(db, pOrderBy);
   sqlite3ExprDelete(db, pLimit);
 #endif
-  sqlite3DbFree(db, aToOpen);
+  if( aToOpen ) sqlite3DbNNFreeNN(db, aToOpen);
   return;
 }
 /* Make sure "isView" and other macros defined above are undefined. Otherwise
diff --git a/src/expr.c b/src/expr.c
index be3e73294..857251292 100644
--- a/src/expr.c
+++ b/src/expr.c
@@ -1220,6 +1220,7 @@ void sqlite3ExprAssignVarNumber(Parse *pParse, Expr *pExpr, u32 n){
 */
 static SQLITE_NOINLINE void sqlite3ExprDeleteNN(sqlite3 *db, Expr *p){
   assert( p!=0 );
+  assert( db!=0 );
   assert( !ExprUseUValue(p) || p->u.iValue>=0 );
   assert( !ExprUseYWin(p) || !ExprUseYSub(p) );
   assert( !ExprUseYWin(p) || p->y.pWin!=0 || db->mallocFailed );
@@ -1252,7 +1253,7 @@ static SQLITE_NOINLINE void sqlite3ExprDeleteNN(sqlite3 *db, Expr *p){
     }
   }
   if( !ExprHasProperty(p, EP_Static) ){
-    sqlite3DbFreeNN(db, p);
+    sqlite3DbNNFreeNN(db, p);
   }
 }
 void sqlite3ExprDelete(sqlite3 *db, Expr *p){
@@ -2038,12 +2039,13 @@ static SQLITE_NOINLINE void exprListDeleteNN(sqlite3 *db, ExprList *pList){
   int i = pList->nExpr;
   struct ExprList_item *pItem =  pList->a;
   assert( pList->nExpr>0 );
+  assert( db!=0 );
   do{
     sqlite3ExprDelete(db, pItem->pExpr);
-    sqlite3DbFree(db, pItem->zEName);
+    if( pItem->zEName ) sqlite3DbNNFreeNN(db, pItem->zEName);
     pItem++;
   }while( --i>0 );
-  sqlite3DbFreeNN(db, pList);
+  sqlite3DbNNFreeNN(db, pList);
 }
 void sqlite3ExprListDelete(sqlite3 *db, ExprList *pList){
   if( pList ) exprListDeleteNN(db, pList);
@@ -6075,6 +6077,7 @@ static int exprRefToSrcList(Walker *pWalker, Expr *pExpr){
 int sqlite3ReferencesSrcList(Parse *pParse, Expr *pExpr, SrcList *pSrcList){
   Walker w;
   struct RefSrcList x;
+  assert( pParse->db!=0 );
   memset(&w, 0, sizeof(w));
   memset(&x, 0, sizeof(x));
   w.xExprCallback = exprRefToSrcList;
@@ -6091,7 +6094,7 @@ int sqlite3ReferencesSrcList(Parse *pParse, Expr *pExpr, SrcList *pSrcList){
     sqlite3WalkExpr(&w, pExpr->y.pWin->pFilter);
   }
 #endif
-  sqlite3DbFree(pParse->db, x.aiExclude);
+  if( x.aiExclude ) sqlite3DbNNFreeNN(pParse->db, x.aiExclude);
   if( w.eCode & 0x01 ){
     return 1;
   }else if( w.eCode ){
diff --git a/src/fkey.c b/src/fkey.c
index a05792514..cae6bb19d 100644
--- a/src/fkey.c
+++ b/src/fkey.c
@@ -1439,11 +1439,12 @@ void sqlite3FkDelete(sqlite3 *db, Table *pTab){
   FKey *pNext;                    /* Copy of pFKey->pNextFrom */
 
   assert( IsOrdinaryTable(pTab) );
+  assert( db!=0 );
   for(pFKey=pTab->u.tab.pFKey; pFKey; pFKey=pNext){
     assert( db==0 || sqlite3SchemaMutexHeld(db, 0, pTab->pSchema) );
 
     /* Remove the FK from the fkeyHash hash table. */
-    if( !db || db->pnBytesFreed==0 ){
+    if( db->pnBytesFreed==0 ){
       if( pFKey->pPrevTo ){
         pFKey->pPrevTo->pNextTo = pFKey->pNextTo;
       }else{
diff --git a/src/insert.c b/src/insert.c
index 6de304848..6c71391a1 100644
--- a/src/insert.c
+++ b/src/insert.c
@@ -1417,7 +1417,7 @@ insert_cleanup:
   sqlite3UpsertDelete(db, pUpsert);
   sqlite3SelectDelete(db, pSelect);
   sqlite3IdListDelete(db, pColumn);
-  sqlite3DbFree(db, aRegIdx);
+  if( aRegIdx ) sqlite3DbNNFreeNN(db, aRegIdx);
 }
 
 /* Make sure "isView" and other macros defined above are undefined. Otherwise
diff --git a/src/malloc.c b/src/malloc.c
index c508bf752..d0ed48dba 100644
--- a/src/malloc.c
+++ b/src/malloc.c
@@ -441,6 +441,41 @@ void sqlite3DbFreeNN(sqlite3 *db, void *p){
   sqlite3MemdebugSetType(p, MEMTYPE_HEAP);
   sqlite3_free(p);
 }
+void sqlite3DbNNFreeNN(sqlite3 *db, void *p){
+  assert( db!=0 );
+  assert( sqlite3_mutex_held(db->mutex) );
+  assert( p!=0 );
+  if( db->pnBytesFreed ){
+    measureAllocationSize(db, p);
+    return;
+  }
+  if( ((uptr)p)<(uptr)(db->lookaside.pEnd) ){
+#ifndef SQLITE_OMIT_TWOSIZE_LOOKASIDE
+    if( ((uptr)p)>=(uptr)(db->lookaside.pMiddle) ){
+      LookasideSlot *pBuf = (LookasideSlot*)p;
+#ifdef SQLITE_DEBUG
+      memset(p, 0xaa, LOOKASIDE_SMALL);  /* Trash freed content */
+#endif
+      pBuf->pNext = db->lookaside.pSmallFree;
+      db->lookaside.pSmallFree = pBuf;
+      return;
+    }
+#endif /* SQLITE_OMIT_TWOSIZE_LOOKASIDE */
+    if( ((uptr)p)>=(uptr)(db->lookaside.pStart) ){
+      LookasideSlot *pBuf = (LookasideSlot*)p;
+#ifdef SQLITE_DEBUG
+      memset(p, 0xaa, db->lookaside.szTrue);  /* Trash freed content */
+#endif
+      pBuf->pNext = db->lookaside.pFree;
+      db->lookaside.pFree = pBuf;
+      return;
+    }
+  }
+  assert( sqlite3MemdebugHasType(p, (MEMTYPE_LOOKASIDE|MEMTYPE_HEAP)) );
+  assert( sqlite3MemdebugNoType(p, (u8)~(MEMTYPE_LOOKASIDE|MEMTYPE_HEAP)) );
+  sqlite3MemdebugSetType(p, MEMTYPE_HEAP);
+  sqlite3_free(p);
+}
 void sqlite3DbFree(sqlite3 *db, void *p){
   assert( db==0 || sqlite3_mutex_held(db->mutex) );
   if( p ) sqlite3DbFreeNN(db, p);
diff --git a/src/prepare.c b/src/prepare.c
index f55ff72fc..f66c366b9 100644
--- a/src/prepare.c
+++ b/src/prepare.c
@@ -574,15 +574,15 @@ void sqlite3ParseObjectReset(Parse *pParse){
   assert( db->pParse==pParse );
   assert( pParse->nested==0 );
 #ifndef SQLITE_OMIT_SHARED_CACHE
-  sqlite3DbFree(db, pParse->aTableLock);
+  if( pParse->aTableLock ) sqlite3DbNNFreeNN(db, pParse->aTableLock);
 #endif
   while( pParse->pCleanup ){
     ParseCleanup *pCleanup = pParse->pCleanup;
     pParse->pCleanup = pCleanup->pNext;
     pCleanup->xCleanup(db, pCleanup->pPtr);
-    sqlite3DbFreeNN(db, pCleanup);
+    sqlite3DbNNFreeNN(db, pCleanup);
   }
-  sqlite3DbFree(db, pParse->aLabel);
+  if( pParse->aLabel ) sqlite3DbNNFreeNN(db, pParse->aLabel);
   if( pParse->pConstExpr ){
     sqlite3ExprListDelete(db, pParse->pConstExpr);
   }
diff --git a/src/select.c b/src/select.c
index 3f80e44ce..39ec70f2b 100644
--- a/src/select.c
+++ b/src/select.c
@@ -76,6 +76,7 @@ struct SortCtx {
 ** If bFree==0, Leave the first Select object unfreed
 */
 static void clearSelect(sqlite3 *db, Select *p, int bFree){
+  assert( db!=0 );
   while( p ){
     Select *pPrior = p->pPrior;
     sqlite3ExprListDelete(db, p->pEList);
@@ -95,7 +96,7 @@ static void clearSelect(sqlite3 *db, Select *p, int bFree){
       sqlite3WindowUnlinkFromSelect(p->pWin);
     }
 #endif
-    if( bFree ) sqlite3DbFreeNN(db, p);
+    if( bFree ) sqlite3DbNNFreeNN(db, p);
     p = pPrior;
     bFree = 1;
   }
@@ -1501,9 +1502,10 @@ KeyInfo *sqlite3KeyInfoAlloc(sqlite3 *db, int N, int X){
 */
 void sqlite3KeyInfoUnref(KeyInfo *p){
   if( p ){
+    assert( p->db!=0 );
     assert( p->nRef>0 );
     p->nRef--;
-    if( p->nRef==0 ) sqlite3DbFreeNN(p->db, p);
+    if( p->nRef==0 ) sqlite3DbNNFreeNN(p->db, p);
   }
 }
 
diff --git a/src/sqliteInt.h b/src/sqliteInt.h
index 32e0e78e8..c53b4f3bb 100644
--- a/src/sqliteInt.h
+++ b/src/sqliteInt.h
@@ -4364,6 +4364,7 @@ void *sqlite3DbReallocOrFree(sqlite3 *, void *, u64);
 void *sqlite3DbRealloc(sqlite3 *, void *, u64);
 void sqlite3DbFree(sqlite3*, void*);
 void sqlite3DbFreeNN(sqlite3*, void*);
+void sqlite3DbNNFreeNN(sqlite3*, void*);
 int sqlite3MallocSize(const void*);
 int sqlite3DbMallocSize(sqlite3*, const void*);
 void *sqlite3PageMalloc(int);
diff --git a/src/tokenize.c b/src/tokenize.c
index b147cdb40..8dac9ece5 100644
--- a/src/tokenize.c
+++ b/src/tokenize.c
@@ -711,7 +711,7 @@ int sqlite3RunParser(Parse *pParse, const char *zSql){
   if( pParse->pNewTrigger && !IN_RENAME_OBJECT ){
     sqlite3DeleteTrigger(db, pParse->pNewTrigger);
   }
-  if( pParse->pVList ) sqlite3DbFreeNN(db, pParse->pVList);
+  if( pParse->pVList ) sqlite3DbNNFreeNN(db, pParse->pVList);
   db->pParse = pParentParse;
   assert( nErr==0 || pParse->rc!=SQLITE_OK );
   return nErr;
diff --git a/src/vdbeaux.c b/src/vdbeaux.c
index 8ab7978fa..ca711d8d0 100644
--- a/src/vdbeaux.c
+++ b/src/vdbeaux.c
@@ -884,7 +884,7 @@ static void resolveP2Values(Vdbe *p, int *pMaxFuncArgs){
   }
 resolve_p2_values_loop_exit:
   if( aLabel ){
-    sqlite3DbFreeNN(p->db, pParse->aLabel);
+    sqlite3DbNNFreeNN(p->db, pParse->aLabel);
     pParse->aLabel = 0;
   }
   pParse->nLabel = 0;
@@ -1195,8 +1195,9 @@ void sqlite3VdbeJumpHereOrPopInst(Vdbe *p, int addr){
 ** the FuncDef is not ephermal, then do nothing.
 */
 static void freeEphemeralFunction(sqlite3 *db, FuncDef *pDef){
+  assert( db!=0 );
   if( (pDef->funcFlags & SQLITE_FUNC_EPHEM)!=0 ){
-    sqlite3DbFreeNN(db, pDef);
+    sqlite3DbNNFreeNN(db, pDef);
   }
 }
 
@@ -1205,11 +1206,12 @@ static void freeEphemeralFunction(sqlite3 *db, FuncDef *pDef){
 */
 static SQLITE_NOINLINE void freeP4Mem(sqlite3 *db, Mem *p){
   if( p->szMalloc ) sqlite3DbFree(db, p->zMalloc);
-  sqlite3DbFreeNN(db, p);
+  sqlite3DbNNFreeNN(db, p);
 }
 static SQLITE_NOINLINE void freeP4FuncCtx(sqlite3 *db, sqlite3_context *p){
+  assert( db!=0 );
   freeEphemeralFunction(db, p->pFunc);
-  sqlite3DbFreeNN(db, p);
+  sqlite3DbNNFreeNN(db, p);
 }
 static void freeP4(sqlite3 *db, int p4type, void *p4){
   assert( db );
@@ -1222,7 +1224,7 @@ static void freeP4(sqlite3 *db, int p4type, void *p4){
     case P4_INT64:
     case P4_DYNAMIC:
     case P4_INTARRAY: {
-      sqlite3DbFree(db, p4);
+      if( p4 ) sqlite3DbNNFreeNN(db, p4);
       break;
     }
     case P4_KEYINFO: {
@@ -1261,6 +1263,7 @@ static void freeP4(sqlite3 *db, int p4type, void *p4){
 */
 static void vdbeFreeOpArray(sqlite3 *db, Op *aOp, int nOp){
   assert( nOp>=0 );
+  assert( db!=0 );
   if( aOp ){
     Op *pOp = &aOp[nOp-1];
     while(1){  /* Exit via break */
@@ -1271,7 +1274,7 @@ static void vdbeFreeOpArray(sqlite3 *db, Op *aOp, int nOp){
       if( pOp==aOp ) break;
       pOp--;
     }
-    sqlite3DbFreeNN(db, aOp);
+    sqlite3DbNNFreeNN(db, aOp);
   }
 }
 
@@ -2025,7 +2028,7 @@ static void releaseMemArray(Mem *p, int N){
         sqlite3VdbeMemRelease(p);
         p->flags = MEM_Undefined;
       }else if( p->szMalloc ){
-        sqlite3DbFreeNN(db, p->zMalloc);
+        sqlite3DbNNFreeNN(db, p->zMalloc);
         p->szMalloc = 0;
         p->flags = MEM_Undefined;
       }
@@ -3546,10 +3549,11 @@ void sqlite3VdbeDeleteAuxData(sqlite3 *db, AuxData **pp, int iOp, int mask){
 */
 static void sqlite3VdbeClearObject(sqlite3 *db, Vdbe *p){
   SubProgram *pSub, *pNext;
+  assert( db!=0 );
   assert( p->db==0 || p->db==db );
   if( p->aColName ){
     releaseMemArray(p->aColName, p->nResColumn*COLNAME_N);
-    sqlite3DbFreeNN(db, p->aColName);
+    sqlite3DbNNFreeNN(db, p->aColName);
   }
   for(pSub=p->pProgram; pSub; pSub=pNext){
     pNext = pSub->pNext;
@@ -3558,11 +3562,11 @@ static void sqlite3VdbeClearObject(sqlite3 *db, Vdbe *p){
   }
   if( p->eVdbeState!=VDBE_INIT_STATE ){
     releaseMemArray(p->aVar, p->nVar);
-    if( p->pVList ) sqlite3DbFreeNN(db, p->pVList);
-    if( p->pFree ) sqlite3DbFreeNN(db, p->pFree);
+    if( p->pVList ) sqlite3DbNNFreeNN(db, p->pVList);
+    if( p->pFree ) sqlite3DbNNFreeNN(db, p->pFree);
   }
   vdbeFreeOpArray(db, p->aOp, p->nOp);
-  sqlite3DbFree(db, p->zSql);
+  if( p->zSql ) sqlite3DbNNFreeNN(db, p->zSql);
 #ifdef SQLITE_ENABLE_NORMALIZE
   sqlite3DbFree(db, p->zNormSql);
   {
@@ -3592,6 +3596,7 @@ void sqlite3VdbeDelete(Vdbe *p){
 
   assert( p!=0 );
   db = p->db;
+  assert( db!=0 );
   assert( sqlite3_mutex_held(db->mutex) );
   sqlite3VdbeClearObject(db, p);
   if( db->pnBytesFreed==0 ){
@@ -3605,7 +3610,7 @@ void sqlite3VdbeDelete(Vdbe *p){
       p->pNext->pPrev = p->pPrev;
     }
   }
-  sqlite3DbFreeNN(db, p);
+  sqlite3DbNNFreeNN(db, p);
 }
 
 /*
@@ -5221,13 +5226,14 @@ void sqlite3VtabImportErrmsg(Vdbe *p, sqlite3_vtab *pVtab){
 ** the vdbeUnpackRecord() function found in vdbeapi.c.
 */
 static void vdbeFreeUnpacked(sqlite3 *db, int nField, UnpackedRecord *p){
+  assert( db!=0 );
   if( p ){
     int i;
     for(i=0; i<nField; i++){
       Mem *pMem = &p->aMem[i];
       if( pMem->zMalloc ) sqlite3VdbeMemReleaseMalloc(pMem);
     }
-    sqlite3DbFreeNN(db, p);
+    sqlite3DbNNFreeNN(db, p);
   }
 }
 #endif /* SQLITE_ENABLE_PREUPDATE_HOOK */
@@ -5298,7 +5304,7 @@ void sqlite3VdbePreUpdateHook(
     for(i=0; i<pCsr->nField; i++){
       sqlite3VdbeMemRelease(&preupdate.aNew[i]);
     }
-    sqlite3DbFreeNN(db, preupdate.aNew);
+    sqlite3DbNNFreeNN(db, preupdate.aNew);
   }
 }
 #endif /* SQLITE_ENABLE_PREUPDATE_HOOK */
diff --git a/src/vtab.c b/src/vtab.c
index b50ccd24a..9bf031faf 100644
--- a/src/vtab.c
+++ b/src/vtab.c
@@ -340,7 +340,8 @@ void sqlite3VtabUnlockList(sqlite3 *db){
 */
 void sqlite3VtabClear(sqlite3 *db, Table *p){
   assert( IsVirtual(p) );
-  if( !db || db->pnBytesFreed==0 ) vtabDisconnectAll(0, p);
+  assert( db!=0 );
+  if( db->pnBytesFreed==0 ) vtabDisconnectAll(0, p);
   if( p->u.vtab.azArg ){
     int i;
     for(i=0; i<p->u.vtab.nArg; i++){
diff --git a/src/where.c b/src/where.c
index 9c4678345..0a6f5e627 100644
--- a/src/where.c
+++ b/src/where.c
@@ -2251,8 +2251,9 @@ static int whereLoopXfer(sqlite3 *db, WhereLoop *pTo, WhereLoop *pFrom){
 ** Delete a WhereLoop object
 */
 static void whereLoopDelete(sqlite3 *db, WhereLoop *p){
+  assert( db!=0 );
   whereLoopClear(db, p);
-  sqlite3DbFreeNN(db, p);
+  sqlite3DbNNFreeNN(db, p);
 }
 
 /*
@@ -2260,6 +2261,7 @@ static void whereLoopDelete(sqlite3 *db, WhereLoop *p){
 */
 static void whereInfoFree(sqlite3 *db, WhereInfo *pWInfo){
   assert( pWInfo!=0 );
+  assert( db!=0 );
   sqlite3WhereClauseClear(&pWInfo->sWC);
   while( pWInfo->pLoops ){
     WhereLoop *p = pWInfo->pLoops;
@@ -2269,10 +2271,10 @@ static void whereInfoFree(sqlite3 *db, WhereInfo *pWInfo){
   assert( pWInfo->pExprMods==0 );
   while( pWInfo->pMemToFree ){
     WhereMemBlock *pNext = pWInfo->pMemToFree->pNext;
-    sqlite3DbFreeNN(db, pWInfo->pMemToFree);
+    sqlite3DbNNFreeNN(db, pWInfo->pMemToFree);
     pWInfo->pMemToFree = pNext;
   }
-  sqlite3DbFreeNN(db, pWInfo);
+  sqlite3DbNNFreeNN(db, pWInfo);
 }
 
 /* Undo all Expr node modifications
@@ -5073,7 +5075,8 @@ static int wherePathSolver(WhereInfo *pWInfo, LogEst nRowEst){
   pWInfo->nRowOut = pFrom->nRow;
 
   /* Free temporary memory and return success */
-  sqlite3DbFreeNN(db, pSpace);
+  assert( db!=0 );
+  sqlite3DbNNFreeNN(db, pSpace);
   return SQLITE_OK;
 }
 
diff --git a/src/wherecode.c b/src/wherecode.c
index 85df64279..4c34ea0dc 100644
--- a/src/wherecode.c
+++ b/src/wherecode.c
@@ -2109,8 +2109,8 @@ Bitmask sqlite3WhereCodeOneLoopStart(
       }
       nConstraint++;
     }
-    sqlite3DbFree(db, zStartAff);
-    sqlite3DbFree(db, zEndAff);
+    if( zStartAff ) sqlite3DbNNFreeNN(db, zStartAff);
+    if( zEndAff ) sqlite3DbNNFreeNN(db, zEndAff);
 
     /* Top of the loop body */
     if( pLevel->p2==0 ) pLevel->p2 = sqlite3VdbeCurrentAddr(v);