Claw back most of the performance lost in the previous commit.

FossilOrigin-Name: df8ce2675b070fcdc338918e7652a26ffc90439fe399ceac206fadf8a93a681f

manifest

@@ -1,5 +1,5 @@
-C Modify\sUPDATE\sso\sthat\stwo-pass\supdates\son\sa\srowid\stable\suse\san\sephemeral\ntable\sto\sstore\srowids\srather\sthan\sa\sRowSet.\s\sThis\suses\sless\smemory,\sthough\nit\sis\sslower.
-D 2020-11-14T20:03:34.128
+C Claw\sback\smost\sof\sthe\sperformance\slost\sin\sthe\sprevious\scommit.
+D 2020-11-17T21:26:13.913
 F .fossil-settings/empty-dirs dbb81e8fc0401ac46a1491ab34a7f2c7c0452f2f06b54ebb845d024ca8283ef1
 F .fossil-settings/ignore-glob 35175cdfcf539b2318cb04a9901442804be81cd677d8b889fcc9149c21f239ea
 F LICENSE.md df5091916dbb40e6e9686186587125e1b2ff51f022cc334e886c19a0e9982724
@@ -604,12 +604,12 @@ F src/threads.c 4ae07fa022a3dc7c5beb373cf744a85d3c5c6c3c
 F src/tokenize.c 4dc01b267593537e2a0d0efe9f80dabe24c5b6f7627bc6971c487fa6a1dacbbf
 F src/treeview.c 4b92992176fb2caefbe06ba5bd06e0e0ebcde3d5564758da672631f17aa51cda
 F src/trigger.c 515e79206d40d1d4149129318582e79a6e9db590a7b74e226fdb5b2a6c7e1b10
-F src/update.c 5d9894b53209e42f57141f1b3d9d86361993049c42b393243abbee0f4bdd49fa
+F src/update.c 9f126204a6acb96bbe47391ae48e0fc579105d8e76a6d9c4fab3271367476580
 F src/upsert.c 2920de71b20f04fe25eb00b655d086f0ba60ea133c59d7fa3325c49838818e78
 F src/utf.c ee39565f0843775cc2c81135751ddd93eceb91a673ea2c57f61c76f288b041a0
 F src/util.c c0c7977de7ef9b8cb10f6c85f2d0557889a658f817b0455909a49179ba4c8002
 F src/vacuum.c 492422c1463c076473bae1858799c7a0a5fe87a133d1223239447c422cd26286
-F src/vdbe.c 6f3fb4f058c478b38c5280ccfc939745076c6a693999e49846c99fdc761c9c90
+F src/vdbe.c 59e8caad2c5520c942ee8321a008991a0d36be2b0641fd16dd941d89e781ea97
 F src/vdbe.h 83603854bfa5851af601fc0947671eb260f4363e62e960e8a994fb9bbcd2aaa1
 F src/vdbeInt.h 3ca5e9fd6e095a8b6cf6bc3587a46fc93499503b2fe48951e1034ba9e2ce2f6e
 F src/vdbeapi.c c5e7cb2ab89a24d7f723e87b508f21bfb1359a04db5277d8a99fd1e015c12eb9
@@ -1883,10 +1883,7 @@ F vsixtest/vsixtest.tcl 6a9a6ab600c25a91a7acc6293828957a386a8a93
 F vsixtest/vsixtest.vcxproj.data 2ed517e100c66dc455b492e1a33350c1b20fbcdc
 F vsixtest/vsixtest.vcxproj.filters 37e51ffedcdb064aad6ff33b6148725226cd608e
 F vsixtest/vsixtest_TemporaryKey.pfx e5b1b036facdb453873e7084e1cae9102ccc67a0
-P 772ae83c61c87a9004a614d8ec120ba843286bff1edbd20b987fd592ced84d79
-R 87198020f818dc0e1868a0bdd49e2aaf
-T *branch * lowmem-update-exp
-T *sym-lowmem-update-exp *
-T -sym-trunk *
+P 4673096dd8c5ed7aed098ff518a6d01d35c40fad991b89fddd91c19a727a4308
+R 4e4cd284a246b3e7da3720d189e4cd5f
 U drh
-Z 026ca59c1df12878f7c57e2d3cf7ce51
+Z 9ab365bfaa4c57c68b10ad5bd403164d

manifest.uuid

@@ -1 +1 @@
-4673096dd8c5ed7aed098ff518a6d01d35c40fad991b89fddd91c19a727a4308
+df8ce2675b070fcdc338918e7652a26ffc90439fe399ceac206fadf8a93a681f

src/update.c

@@ -652,8 +652,7 @@ void sqlite3Update(
   if( nChangeFrom==0 && HasRowid(pTab) ){
     sqlite3VdbeAddOp3(v, OP_Null, 0, regRowSet, regOldRowid);
     iEph = pParse->nTab++;
-    addrOpen = sqlite3VdbeAddOp2(v, OP_OpenEphemeral, iEph, 0);
-    sqlite3VdbeLoadString(v, regRowSet, "");
+    addrOpen = sqlite3VdbeAddOp3(v, OP_OpenEphemeral, iEph, 0, regRowSet);
   }else{
     assert( pPk!=0 || HasRowid(pTab) );
     nPk = pPk ? pPk->nKeyCol : 0;
@@ -748,7 +747,7 @@ void sqlite3Update(
         aRegIdx[nAllIdx] = ++pParse->nMem;
         sqlite3VdbeAddOp3(v, OP_Insert, iEph, regRowSet, regOldRowid);
       }else{
-        if( addrOpen ) sqlite3VdbeChangeToNoop(v, addrOpen);
+        if( ALWAYS(addrOpen) ) sqlite3VdbeChangeToNoop(v, addrOpen);
       }
     }else{
       /* Read the PK of the current row into an array of registers. In
@@ -1088,11 +1087,9 @@ void sqlite3Update(
   }else if( eOnePass==ONEPASS_MULTI ){
     sqlite3VdbeResolveLabel(v, labelContinue);
     sqlite3WhereEnd(pWInfo);
-  }else /*if( pPk || nChangeFrom )*/{
+  }else{
     sqlite3VdbeResolveLabel(v, labelContinue);
     sqlite3VdbeAddOp2(v, OP_Next, iEph, addrTop); VdbeCoverage(v);
-//  }else{
-//    sqlite3VdbeGoto(v, labelContinue);
   }
   sqlite3VdbeResolveLabel(v, labelBreak);
 

src/vdbe.c

@@ -3901,7 +3901,7 @@ case OP_OpenDup: {
 }
 
 
-/* Opcode: OpenEphemeral P1 P2 * P4 P5
+/* Opcode: OpenEphemeral P1 P2 P3 P4 P5
 ** Synopsis: nColumn=P2
 **
 ** Open a new cursor P1 to a transient table.
@@ -3921,6 +3921,10 @@ case OP_OpenDup: {
 ** in btree.h.  These flags control aspects of the operation of
 ** the btree.  The BTREE_OMIT_JOURNAL and BTREE_SINGLE flags are
 ** added automatically.
+**
+** If P3 is positive, then reg[P3] is modified slightly so that it
+** can be used as zero-length data for OP_Insert.  This is an optimization
+** that avoids an extra OP_Blob opcode to initialize that register.
 */
 /* Opcode: OpenAutoindex P1 P2 * P4 *
 ** Synopsis: nColumn=P2
@@ -3943,6 +3947,15 @@ case OP_OpenEphemeral: {
       SQLITE_OPEN_TRANSIENT_DB;
   assert( pOp->p1>=0 );
   assert( pOp->p2>=0 );
+  if( pOp->p3>0 ){
+    /* Make register reg[P3] into a value that can be used as the data
+    ** form sqlite3BtreeInsert() where the length of the data is zero. */
+    assert( pOp->p2==0 ); /* Only used when number of columns is zero */
+    assert( pOp->opcode==OP_OpenEphemeral );
+    assert( aMem[pOp->p3].flags & MEM_Null );
+    aMem[pOp->p3].n = 0;
+    aMem[pOp->p3].z = "";
+  }
   pCx = p->apCsr[pOp->p1];
   if( pCx && pCx->pBtx ){
     /* If the ephermeral table is already open, erase all existing content
@@ -5102,7 +5115,7 @@ case OP_Insert: {
 
   if( pOp->p5 & OPFLAG_NCHANGE ) p->nChange++;
   if( pOp->p5 & OPFLAG_LASTROWID ) db->lastRowid = x.nKey;
-  assert( pData->flags & (MEM_Blob|MEM_Str) );
+  assert( (pData->flags & (MEM_Blob|MEM_Str))!=0 || pData->n==0 );
   x.pData = pData->z;
   x.nData = pData->n;
   seekResult = ((pOp->p5 & OPFLAG_USESEEKRESULT) ? pC->seekResult : 0);