Optimizations to link list merge sort code in vdbesort.c, pcache.c, and

rowset.c.  Resulting binaries are 10 bytes smaller and use 0.03% fewer CPU
cycles.

FossilOrigin-Name: 9033afbb31b28a8ad6856ac1f773d8e83bc9ec1c

manifest

@@ -1,5 +1,5 @@
-C For\squeries\swith\sboth\sORDER\sBY\sand\sLIMIT,\sif\sthe\srows\sof\sthe\sinner\sloop\sare\nemitted\sin\sORDER\sBY\sorder\sand\sthe\sLIMIT\shas\sbeen\sreached,\sthen\soptimize\sby\nexiting\sthe\sinner\sloop\sand\scontinuing\swith\sthe\snext\scycle\sof\sthe\sfirst\souter\nloop.
-D 2016-05-20T14:11:37.786
+C Optimizations\sto\slink\slist\smerge\ssort\scode\sin\svdbesort.c,\spcache.c,\sand\nrowset.c.\s\sResulting\sbinaries\sare\s10\sbytes\ssmaller\sand\suse\s0.03%\sfewer\sCPU\ncycles.
+D 2016-05-20T14:54:54.663
 F Makefile.in f59e0763ff448719fc1bd25513882b0567286317
 F Makefile.linux-gcc 7bc79876b875010e8c8f9502eb935ca92aa3c434
 F Makefile.msc 306d73e854b1a92ea06e5d1e637faa5c44de53c7
@@ -368,7 +368,7 @@ F src/os_win.h eb7a47aa17b26b77eb97e4823f20a00b8bda12ca
 F src/pager.c 3910579bfbe323dfabed2b95d201159b61b8ef42
 F src/pager.h 329bdf078a4e0a3b35084534d58625d21fd03681
 F src/parse.y 10eb2f3fb62341291528c7984498054731f9d31e
-F src/pcache.c f398c0084399e7481482cbc6a578a3cc4c3675f3
+F src/pcache.c 50fb5728dbfb92461f89f8763ff8b60d0dbeba2c
 F src/pcache.h 2cedcd8407eb23017d92790b112186886e179490
 F src/pcache1.c 7f51d2b541aab57596adf62db2c4bb025d34f04d
 F src/pragma.c faf42922bb7ab2f6672cb550356c1967abae3c84
@@ -377,7 +377,7 @@ F src/prepare.c 22df6171aec1d86904ed2ad30c2348a5748aa04e
 F src/printf.c a5f0ca08ddede803c241266abb46356ec748ded1
 F src/random.c ba2679f80ec82c4190062d756f22d0c358180696
 F src/resolve.c cca3aa77b95706df5d635a2141a4d1de60ae6598
-F src/rowset.c 49eb91c588a2bab36647368e031dc5b66928149d
+F src/rowset.c 7b7e7e479212e65b723bf40128c7b36dc5afdfac
 F src/select.c a0c4abf54bc6bd3a9c77a36ef3d1676045706cb2
 F src/shell.c 14ff7f660530a52b117d110ba3390b7b2eb719b6
 F src/sqlite.h.in 9984129d86243424b765fcb3f147c697bd20bb54
@@ -451,7 +451,7 @@ F src/vdbeapi.c ba85b78fe08dc4a9ce747e62c89a2b4a4547e74c
 F src/vdbeaux.c ace1875da40b7185e604586768d5ac90de7e4f7f
 F src/vdbeblob.c c9f2f494b911c6fa34efd9803f0a10807da80f77
 F src/vdbemem.c 5cfef60e60e19cab6275d1b975bf4c791d575beb
-F src/vdbesort.c 0a8f98366ae794442e6d1ef71d9553226d885d19
+F src/vdbesort.c 91fda3909326860382b0ca8aa251e609c6a9d62c
 F src/vdbetrace.c f75c5455d8cf389ef86a8bfdfd3177e0e3692484
 F src/vtab.c 23b6cdfa996152d43b390504ed4a942c8caf3a00
 F src/vxworks.h d2988f4e5a61a4dfe82c6524dd3d6e4f2ce3cdb9
@@ -1490,8 +1490,7 @@ F vsixtest/vsixtest.tcl 6a9a6ab600c25a91a7acc6293828957a386a8a93
 F vsixtest/vsixtest.vcxproj.data 2ed517e100c66dc455b492e1a33350c1b20fbcdc
 F vsixtest/vsixtest.vcxproj.filters 37e51ffedcdb064aad6ff33b6148725226cd608e
 F vsixtest/vsixtest_TemporaryKey.pfx e5b1b036facdb453873e7084e1cae9102ccc67a0
-P 645bd696dfd86d8c93080f6ebfddbc9639ec088b ed1b30dc932a7c03e173b130c5f55f9989c7e0b4
-R b166646a4114a46c17faadb7ecf63948
-T +closed ed1b30dc932a7c03e173b130c5f55f9989c7e0b4
+P 559733b09e9630fac9d9318a7ecbaba9134e9160
+R db641f928488147ea4b353a0a8e4e73d
 U drh
-Z aa696592564772ea00c367935ddfa343
+Z 8f08ede060795a413d5c246d730b7a0d

manifest.uuid

@@ -1 +1 @@
-559733b09e9630fac9d9318a7ecbaba9134e9160
+9033afbb31b28a8ad6856ac1f773d8e83bc9ec1c

src/pcache.c

@@ -692,23 +692,25 @@ void sqlite3PcacheClear(PCache *pCache){
 static PgHdr *pcacheMergeDirtyList(PgHdr *pA, PgHdr *pB){
   PgHdr result, *pTail;
   pTail = &result;
-  while( pA && pB ){
+  assert( pA!=0 && pB!=0 );
+  for(;;){
     if( pA->pgno<pB->pgno ){
       pTail->pDirty = pA;
       pTail = pA;
       pA = pA->pDirty;
+      if( pA==0 ){
+        pTail->pDirty = pB;
+        break;
+      }
     }else{
       pTail->pDirty = pB;
       pTail = pB;
       pB = pB->pDirty;
-    }
-  }
-  if( pA ){
+      if( pB==0 ){
         pTail->pDirty = pA;
-  }else if( pB ){
-    pTail->pDirty = pB;
-  }else{
-    pTail->pDirty = 0;
+        break;
+      }
+    }
   }
   return result.pDirty;
 }
@@ -750,7 +752,8 @@ static PgHdr *pcacheSortDirtyList(PgHdr *pIn){
   }
   p = a[0];
   for(i=1; i<N_SORT_BUCKET; i++){
-    p = pcacheMergeDirtyList(p, a[i]);
+    if( a[i]==0 ) continue;
+    p = p ? pcacheMergeDirtyList(p, a[i]) : a[i];
   }
   return p;
 }

src/rowset.c

@@ -242,27 +242,25 @@ static struct RowSetEntry *rowSetEntryMerge(
   struct RowSetEntry *pTail;
 
   pTail = &head;
-  while( pA && pB ){
+  assert( pA!=0 && pB!=0 );
+  for(;;){
     assert( pA->pRight==0 || pA->v<=pA->pRight->v );
     assert( pB->pRight==0 || pB->v<=pB->pRight->v );
-    if( pA->v<pB->v ){
-      pTail->pRight = pA;
+    if( pA->v<=pB->v ){
+      if( pA->v<pB->v ) pTail = pTail->pRight = pA;
       pA = pA->pRight;
-      pTail = pTail->pRight;
-    }else if( pB->v<pA->v ){
+      if( pA==0 ){
         pTail->pRight = pB;
+        break;
+      }
+    }else{
+      pTail = pTail->pRight = pB;
       pB = pB->pRight;
-      pTail = pTail->pRight;
-    }else{
-      pA = pA->pRight;
-    }
-  }
-  if( pA ){
-    assert( pA->pRight==0 || pA->v<=pA->pRight->v );
+      if( pB==0 ){
         pTail->pRight = pA;
-  }else{
-    assert( pB==0 || pB->pRight==0 || pB->v<=pB->pRight->v );
-    pTail->pRight = pB;
+        break;
+      }
+    }
   }
   return head.pRight;
 }
@@ -286,9 +284,10 @@ static struct RowSetEntry *rowSetEntrySort(struct RowSetEntry *pIn){
     aBucket[i] = pIn;
     pIn = pNext;
   }
-  pIn = 0;
-  for(i=0; i<sizeof(aBucket)/sizeof(aBucket[0]); i++){
-    pIn = rowSetEntryMerge(pIn, aBucket[i]);
+  pIn = aBucket[0];
+  for(i=1; i<sizeof(aBucket)/sizeof(aBucket[0]); i++){
+    if( aBucket[i]==0 ) continue;
+    pIn = pIn ? rowSetEntryMerge(pIn, aBucket[i]) : aBucket[i];
   }
   return pIn;
 }

src/vdbesort.c

@@ -1342,19 +1342,18 @@ static int vdbeSortAllocUnpacked(SortSubtask *pTask){
 
 /*
 ** Merge the two sorted lists p1 and p2 into a single list.
-** Set *ppOut to the head of the new list.
 */
-static void vdbeSorterMerge(
+static SorterRecord *vdbeSorterMerge(
   SortSubtask *pTask,             /* Calling thread context */
   SorterRecord *p1,               /* First list to merge */
-  SorterRecord *p2,               /* Second list to merge */
-  SorterRecord **ppOut            /* OUT: Head of merged list */
+  SorterRecord *p2                /* Second list to merge */
 ){
   SorterRecord *pFinal = 0;
   SorterRecord **pp = &pFinal;
   int bCached = 0;
 
-  while( p1 && p2 ){
+  assert( p1!=0 && p2!=0 );
+  for(;;){
     int res;
     res = pTask->xCompare(
         pTask, &bCached, SRVAL(p1), p1->nVal, SRVAL(p2), p2->nVal
@@ -1364,15 +1363,22 @@ static void vdbeSorterMerge(
       *pp = p1;
       pp = &p1->u.pNext;
       p1 = p1->u.pNext;
+      if( p1==0 ){
+        *pp = p2;
+        break;
+      }
     }else{
       *pp = p2;
       pp = &p2->u.pNext;
       p2 = p2->u.pNext;
       bCached = 0;
+      if( p2==0 ){
+        *pp = p1;
+        break;
       }
     }
-  *pp = p1 ? p1 : p2;
-  *ppOut = pFinal;
+  }
+  return pFinal;
 }
 
 /*
@@ -1425,7 +1431,7 @@ static int vdbeSorterSort(SortSubtask *pTask, SorterList *pList){
 
     p->u.pNext = 0;
     for(i=0; aSlot[i]; i++){
-      vdbeSorterMerge(pTask, p, aSlot[i], &p);
+      p = vdbeSorterMerge(pTask, p, aSlot[i]);
       aSlot[i] = 0;
     }
     aSlot[i] = p;
@@ -1434,7 +1440,8 @@ static int vdbeSorterSort(SortSubtask *pTask, SorterList *pList){
 
   p = 0;
   for(i=0; i<64; i++){
-    vdbeSorterMerge(pTask, p, aSlot[i], &p);
+    if( aSlot[i]==0 ) continue;
+    p = p ? vdbeSorterMerge(pTask, p, aSlot[i]) : aSlot[i];
   }
   pList->pList = p;