Compute WhereLevel.addrBrk and .addrHalt early so that those labels can be

used to abort loops early.  Use this to improve performance on two more
of the cases described by [forum:/forumpost/52651713ac|forum post 52651713ac].

FossilOrigin-Name: 6fc0b9ac23be6840542982de4bb282ebca1db8b5ab3baefdde95a997c1506e81

3 files changed, 27 insertions, 11 deletions

diff --git a/src/where.c b/src/where.c
index 11e24a8d3..824cfcd8c 100644
--- a/src/where.c
+++ b/src/where.c
@@ -1201,7 +1201,9 @@ static SQLITE_NOINLINE void constructAutomaticIndex(
     VdbeCoverage(v);
     VdbeComment((v, "next row of %s", pSrc->pSTab->zName));
   }else{
-    addrTop = sqlite3VdbeAddOp1(v, OP_Rewind, pLevel->iTabCur); VdbeCoverage(v);
+    assert( pLevel->addrHalt );
+    addrTop = sqlite3VdbeAddOp2(v, OP_Rewind,pLevel->iTabCur,pLevel->addrHalt);
+    VdbeCoverage(v);
   }
   if( pPartial ){
     iContinue = sqlite3VdbeMakeLabel(pParse);
@@ -1229,11 +1231,14 @@ static SQLITE_NOINLINE void constructAutomaticIndex(
                           pSrc->u4.pSubq->regResult, pLevel->iIdxCur);
     sqlite3VdbeGoto(v, addrTop);
     pSrc->fg.viaCoroutine = 0;
+    sqlite3VdbeJumpHere(v, addrTop);
   }else{
     sqlite3VdbeAddOp2(v, OP_Next, pLevel->iTabCur, addrTop+1); VdbeCoverage(v);
     sqlite3VdbeChangeP5(v, SQLITE_STMTSTATUS_AUTOINDEX);
+    if( (pSrc->fg.jointype & JT_LEFT)!=0 ){
+      sqlite3VdbeJumpHere(v, addrTop);
+    }
   }
-  sqlite3VdbeJumpHere(v, addrTop);
   sqlite3ReleaseTempReg(pParse, regRecord);
  
   /* Jump here when skipping the initialization */
@@ -7070,6 +7075,12 @@ WhereInfo *sqlite3WhereBegin(
     pTab = pTabItem->pSTab;
     iDb = sqlite3SchemaToIndex(db, pTab->pSchema);
     pLoop = pLevel->pWLoop;
+    pLevel->addrBrk = sqlite3VdbeMakeLabel(pParse);
+    if( ii==0 || (pTabItem[0].fg.jointype & JT_LEFT)!=0 ){
+      pLevel->addrHalt = pLevel->addrBrk;
+    }else{
+      pLevel->addrHalt = pWInfo->a[ii-1].addrHalt;
+    }
     if( (pTab->tabFlags & TF_Ephemeral)!=0 || IsView(pTab) ){
       /* Do nothing */
     }else
@@ -7200,6 +7211,7 @@ WhereInfo *sqlite3WhereBegin(
      && (pLevel->pRJ = sqlite3WhereMalloc(pWInfo, sizeof(WhereRightJoin)))!=0
     ){
       WhereRightJoin *pRJ = pLevel->pRJ;
+      pLevel->addrHalt = pLevel->addrBrk;
       pRJ->iMatch = pParse->nTab++;
       pRJ->regBloom = ++pParse->nMem;
       sqlite3VdbeAddOp2(v, OP_Blob, 65536, pRJ->regBloom);
diff --git a/src/whereInt.h b/src/whereInt.h
index 3a9353e07..09e02c8c7 100644
--- a/src/whereInt.h
+++ b/src/whereInt.h
@@ -75,6 +75,7 @@ struct WhereLevel {
   int iTabCur;          /* The VDBE cursor used to access the table */
   int iIdxCur;          /* The VDBE cursor used to access pIdx */
   int addrBrk;          /* Jump here to break out of the loop */
+  int addrHalt;         /* Abort the query due to empty table or similar */
   int addrNxt;          /* Jump here to start the next IN combination */
   int addrSkip;         /* Jump here for next iteration of skip-scan */
   int addrCont;         /* Jump here to continue with the next loop cycle */
diff --git a/src/wherecode.c b/src/wherecode.c
index 9581ac389..c5fa7a213 100644
--- a/src/wherecode.c
+++ b/src/wherecode.c
@@ -1400,6 +1400,7 @@ static SQLITE_NOINLINE void filterPullDown(
   int addrNxt,         /* Jump here to bypass inner loops */
   Bitmask notReady     /* Loops that are not ready */
 ){
+  int saved_addrBrk;
   while( ++iLevel < pWInfo->nLevel ){
     WhereLevel *pLevel = &pWInfo->a[iLevel];
     WhereLoop *pLoop = pLevel->pWLoop;
@@ -1408,7 +1409,7 @@ static SQLITE_NOINLINE void filterPullDown(
     /*         ,--- Because sqlite3ConstructBloomFilter() has will not have set
     **  vvvvv--'    pLevel->regFilter if this were true. */
     if( NEVER(pLoop->prereq & notReady) ) continue;
-    assert( pLevel->addrBrk==0 );
+    saved_addrBrk = pLevel->addrBrk;
     pLevel->addrBrk = addrNxt;
     if( pLoop->wsFlags & WHERE_IPK ){
       WhereTerm *pTerm = pLoop->aLTerm[0];
@@ -1438,7 +1439,7 @@ static SQLITE_NOINLINE void filterPullDown(
       VdbeCoverage(pParse->pVdbe);
     }
     pLevel->regFilter = 0;
-    pLevel->addrBrk = 0;
+    pLevel->addrBrk = saved_addrBrk;
   }
 }
 
@@ -1485,7 +1486,6 @@ Bitmask sqlite3WhereCodeOneLoopStart(
   sqlite3 *db;                    /* Database connection */
   SrcItem *pTabItem;              /* FROM clause term being coded */
   int addrBrk;                    /* Jump here to break out of the loop */
-  int addrHalt;                   /* addrBrk for the outermost loop */
   int addrCont;                   /* Jump here to continue with next cycle */
   int iRowidReg = 0;        /* Rowid is stored in this register, if not zero */
   int iReleaseReg = 0;      /* Temp register to free before returning */
@@ -1529,7 +1529,7 @@ Bitmask sqlite3WhereCodeOneLoopStart(
   ** there are no IN operators in the constraints, the "addrNxt" label
   ** is the same as "addrBrk".
   */
-  addrBrk = pLevel->addrBrk = pLevel->addrNxt = sqlite3VdbeMakeLabel(pParse);
+  addrBrk = pLevel->addrNxt = pLevel->addrBrk;
   addrCont = pLevel->addrCont = sqlite3VdbeMakeLabel(pParse);
 
   /* If this is the right table of a LEFT OUTER JOIN, allocate and
@@ -1545,13 +1545,16 @@ Bitmask sqlite3WhereCodeOneLoopStart(
     VdbeComment((v, "init LEFT JOIN match flag"));
   }
 
-  /* Compute a safe address to jump to if we discover that the table for
-  ** this loop is empty and can never contribute content. */
+#ifdef SQLITE_DEBUG
+  /* Re-compute the address to jump to if we discover that the table for
+  ** this loop is empty and can never contribute content.  Verify that the
+  ** computation here agrees with the one in sqlite3WhereBegin(). */
   for(j=iLevel; j>0; j--){
     if( pWInfo->a[j].iLeftJoin ) break;
     if( pWInfo->a[j].pRJ ) break;
   }
-  addrHalt = pWInfo->a[j].addrBrk;
+  assert( pWInfo->a[j].addrBrk==pLevel->addrHalt );
+#endif
 
   /* Special case of a FROM clause subquery implemented as a co-routine */
   if( pTabItem->fg.viaCoroutine ){
@@ -1791,7 +1794,7 @@ Bitmask sqlite3WhereCodeOneLoopStart(
       VdbeCoverageIf(v, pX->op==TK_GE);
       sqlite3ReleaseTempReg(pParse, rTemp);
     }else{
-      sqlite3VdbeAddOp2(v, bRev ? OP_Last : OP_Rewind, iCur, addrHalt);
+      sqlite3VdbeAddOp2(v, bRev ? OP_Last : OP_Rewind, iCur, pLevel->addrHalt);
       VdbeCoverageIf(v, bRev==0);
       VdbeCoverageIf(v, bRev!=0);
     }
@@ -2586,7 +2589,7 @@ Bitmask sqlite3WhereCodeOneLoopStart(
       codeCursorHint(pTabItem, pWInfo, pLevel, 0);
       pLevel->op = aStep[bRev];
       pLevel->p1 = iCur;
-      pLevel->p2 = 1 + sqlite3VdbeAddOp2(v, aStart[bRev], iCur, addrHalt);
+      pLevel->p2 = 1 + sqlite3VdbeAddOp2(v, aStart[bRev],iCur,pLevel->addrHalt);
       VdbeCoverageIf(v, bRev==0);
       VdbeCoverageIf(v, bRev!=0);
       pLevel->p5 = SQLITE_STMTSTATUS_FULLSCAN_STEP;