[sqlite] [patch] avoid dynamic alloc in vdbeSorterSort(...)

[Dominique Pellé]

Hi

Below is a patch which avoids a dynamic
allocation in vdbeSorterSort(...), using a local
stack array instead (faster and smaller code).
I assume that a local array of 64 pointers is small
enough to be in the stack.

Is this worth merging?

$ fossil diff  src/vdbesort.c
Index: src/vdbesort.c
==================================================================
--- src/vdbesort.c
+++ src/vdbesort.c
@@ -1394,25 +1394,20 @@
 ** SQLITE_OK if successful, or an SQLite error code (i.e. SQLITE_NOMEM) if
 ** an error occurs.
 */
 static int vdbeSorterSort(SortSubtask *pTask, SorterList *pList){
   int i;
-  SorterRecord **aSlot;
+  SorterRecord *aSlot[64] = { 0 };
   SorterRecord *p;
   int rc;

   rc = vdbeSortAllocUnpacked(pTask);
   if( rc!=SQLITE_OK ) return rc;

   p = pList->pList;
   pTask->xCompare = vdbeSorterGetCompare(pTask->pSorter);

-  aSlot = (SorterRecord **)sqlite3MallocZero(64 * sizeof(SorterRecord *));
-  if( !aSlot ){
-    return SQLITE_NOMEM_BKPT;
-  }
-
   while( p ){
     SorterRecord *pNext;
     if( pList->aMemory ){
       if( (u8*)p==pList->aMemory ){
         pNext = 0;
@@ -1438,11 +1433,10 @@
     if( aSlot[i]==0 ) continue;
     p = p ? vdbeSorterMerge(pTask, p, aSlot[i]) : aSlot[i];
   }
   pList->pList = p;

-  sqlite3_free(aSlot);
   assert( pTask->pUnpacked->errCode==SQLITE_OK
        || pTask->pUnpacked->errCode==SQLITE_NOMEM
   );
   return pTask->pUnpacked->errCode;
 }

Regards
Dominique
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