Invert the meaning of the regBignull flag so that it is 1 when doing the

normal scan and 1 when scanning nulls.  This enables the re-do jump at the
bottom of the loop to be coded with a single OP_IfNotZero opcode, rather
than a sequence of OP_If, OP_Integer, OP_Goto.

FossilOrigin-Name: bf875e1a259a4167694e06349458452dc36c1d38aa6843518d9ae46ce74e5559

manifest

@@ -1,5 +1,5 @@
-C Extra\sVDBE\scomments\sin\sthe\sNULLS\sLAST\slogic\sprovide\slandmarks\sto\shelp\nunderstand\sthe\sEXPLAIN\soutput.
+C Invert\sthe\smeaning\sof\sthe\sregBignull\sflag\sso\sthat\sit\sis\s1\swhen\sdoing\sthe\nnormal\sscan\sand\s1\swhen\sscanning\snulls.\s\sThis\senables\sthe\sre-do\sjump\sat\sthe\nbottom\sof\sthe\sloop\sto\sbe\scoded\swith\sa\ssingle\sOP_IfNotZero\sopcode,\srather\nthan\sa\ssequence\sof\sOP_If,\sOP_Integer,\sOP_Goto.
-D 2019-08-23T13:08:49.776
+D 2019-08-23T13:32:03.306
 F .fossil-settings/empty-dirs dbb81e8fc0401ac46a1491ab34a7f2c7c0452f2f06b54ebb845d024ca8283ef1
 F .fossil-settings/ignore-glob 35175cdfcf539b2318cb04a9901442804be81cd677d8b889fcc9149c21f239ea
 F LICENSE.md df5091916dbb40e6e9686186587125e1b2ff51f022cc334e886c19a0e9982724
@@ -609,9 +609,9 @@ F src/vxworks.h d2988f4e5a61a4dfe82c6524dd3d6e4f2ce3cdb9
 F src/wal.c bbd6838bd79c0a32144d482fb0b6a9d2d1a252fb3b16d5005ec30f2f80413b0d
 F src/wal.h 606292549f5a7be50b6227bd685fa76e3a4affad71bb8ac5ce4cb5c79f6a176a
 F src/walker.c d5a94907dcac990e31976be9dc769d17f6a806782593d6aec9d760ee01ec22cd
-F src/where.c cba20474827dfb3e6bfe7835635e0f018a67d4b8faef4c90d4f28b81b81a8915
+F src/where.c 10e21ac338582a4f87b2d09f09dd812c9bda0a0c4c456f54daeeee355afae733
-F src/whereInt.h cce97c33db637c027bd6f3601a5ff845bd65c833b6465e3b091d48f6a7f51268
+F src/whereInt.h 4a296fd4fa79fdcbc2b5e8c1b898901617655811223e1082b899c23ecb092217
-F src/wherecode.c 1700806bb5bb507ff3614d0836893f35a5a5c438087ee6f373f2ecdf32156d71
+F src/wherecode.c c02ff23ea48b8980d003817bd412e3ce7ce4982159a090566a24cb6101688a9d
 F src/whereexpr.c 2757afbd5cfdbb420f9d0392e1bd5f5c0e33dee50a8c692befc7e502308e449f
 F src/window.c 3ea716bb0dd5ffc8cdbaa48baffc525958b51bc61b2afd73a56baccfcd7ceb2f
 F test/8_3_names.test ebbb5cd36741350040fd28b432ceadf495be25b2
@@ -1837,7 +1837,7 @@ F vsixtest/vsixtest.tcl 6a9a6ab600c25a91a7acc6293828957a386a8a93
 F vsixtest/vsixtest.vcxproj.data 2ed517e100c66dc455b492e1a33350c1b20fbcdc
 F vsixtest/vsixtest.vcxproj.filters 37e51ffedcdb064aad6ff33b6148725226cd608e
 F vsixtest/vsixtest_TemporaryKey.pfx e5b1b036facdb453873e7084e1cae9102ccc67a0
-P d3531f5be7d3769689e2cd8bdc9bab5608759de027d44cc123996f32a4a89583
+P 649b08ead50f10a9ec0357a5e1ed020195d9f93be61ef703ea036a8e53f07a34
-R ab23b496c06c535da116ba045bb5e66a
+R c7fec8ea82d2ec3c4ef608bd58d88fd0
 U drh
-Z 115e4fb3e71b36cfad63bc3458a08668
+Z 0dcd16d55adeefa06ece8236ed711d36

manifest.uuid

@@ -1 +1 @@
-649b08ead50f10a9ec0357a5e1ed020195d9f93be61ef703ea036a8e53f07a34
+bf875e1a259a4167694e06349458452dc36c1d38aa6843518d9ae46ce74e5559

src/where.c

@@ -5218,13 +5218,7 @@ void sqlite3WhereEnd(WhereInfo *pWInfo){
       VdbeCoverageIf(v, pLevel->op==OP_VNext);
       if( pLevel->regBignull ){
         sqlite3VdbeResolveLabel(v, pLevel->addrBignull);
-        addr = sqlite3VdbeAddOp1(v, OP_If, pLevel->regBignull);
+        sqlite3VdbeAddOp2(v, OP_IfNotZero, pLevel->regBignull, pLevel->p2-1);
-        VdbeComment((v, "If NULL-scan done"));
-        VdbeCoverage(v);
-        sqlite3VdbeAddOp2(v, OP_Integer, 1, pLevel->regBignull);
-        sqlite3VdbeAddOp2(v, OP_Goto, 0, pLevel->p2-1);
-        VdbeComment((v, "Do the NULL-scan"));
-        sqlite3VdbeJumpHere(v, addr);
       }
 #ifndef SQLITE_DISABLE_SKIPAHEAD_DISTINCT
       if( addrSeek ) sqlite3VdbeJumpHere(v, addrSeek);

src/whereInt.h

@@ -71,7 +71,7 @@ struct WhereLevel {
   int addrCont;         /* Jump here to continue with the next loop cycle */
   int addrFirst;        /* First instruction of interior of the loop */
   int addrBody;         /* Beginning of the body of this loop */
-  int regBignull;       /* big-null flag reg. True if NULLs not yet scanned */
+  int regBignull;       /* big-null flag reg. True if a NULL-scan is needed */
   int addrBignull;      /* Jump here for next part of big-null scan */
 #ifndef SQLITE_LIKE_DOESNT_MATCH_BLOBS
   u32 iLikeRepCntr;     /* LIKE range processing counter register (times 2) */

src/wherecode.c

@@ -1690,8 +1690,8 @@ Bitmask sqlite3WhereCodeOneLoopStart(
         sqlite3VdbeAddOp1(v, OP_SeekHit, iIdxCur);
       }
       if( regBignull ){
-        sqlite3VdbeAddOp2(v, OP_Integer, 0, regBignull);
+        sqlite3VdbeAddOp2(v, OP_Integer, 1, regBignull);
-        VdbeComment((v, "NULL-scan flag"));
+        VdbeComment((v, "NULL-scan needed flag"));
       }
 
       op = aStartOp[(start_constraints<<2) + (startEq<<1) + bRev];
@@ -1776,8 +1776,8 @@ Bitmask sqlite3WhereCodeOneLoopStart(
     /* Check if the index cursor is past the end of the range. */
     if( nConstraint ){
       if( regBignull ){
-        sqlite3VdbeAddOp2(v, OP_If, regBignull, sqlite3VdbeCurrentAddr(v)+3);
+        sqlite3VdbeAddOp2(v, OP_IfNot, regBignull, sqlite3VdbeCurrentAddr(v)+3);
-        VdbeComment((v, "If in NULL-scan"));
+        VdbeComment((v, "If NULL-scan active"));
         VdbeCoverage(v);
       }
       op = aEndOp[bRev*2 + endEq];
@@ -1788,8 +1788,8 @@ Bitmask sqlite3WhereCodeOneLoopStart(
       testcase( op==OP_IdxLE );  VdbeCoverageIf(v, op==OP_IdxLE );
     }
     if( regBignull ){
-      sqlite3VdbeAddOp2(v, OP_IfNot, regBignull, sqlite3VdbeCurrentAddr(v)+2);
+      sqlite3VdbeAddOp2(v, OP_If, regBignull, sqlite3VdbeCurrentAddr(v)+2);
-      VdbeComment((v, "If not in NULL-scan"));
+      VdbeComment((v, "If NULL-scan pending"));
       VdbeCoverage(v);
       if( bStopAtNull ){
         op = aEndOp[bRev*2 + 0];