Change the OP_Last opcode so that it is a no-op if the cursor is already

pointing at the end of the b-tree.

FossilOrigin-Name: 663473850c4274270445b3771911fa773a8c405f

manifest

@@ -1,5 +1,5 @@
-C Make\sthe\sVACUUM\scommand\sabout\s9%\sfaster\sby\savoiding\sunnecessary\scalls\nto\ssqlite3BtreeMovetoUnpacked()\swhile\scopying\srowid\stables.
-D 2016-11-15T02:46:39.239
+C Change\sthe\sOP_Last\sopcode\sso\sthat\sit\sis\sa\sno-op\sif\sthe\scursor\sis\salready\npointing\sat\sthe\send\sof\sthe\sb-tree.
+D 2016-11-15T04:00:24.244
 F Makefile.in 6b572807415d3f0a379cebc9461416d8df4a12c8
 F Makefile.linux-gcc 7bc79876b875010e8c8f9502eb935ca92aa3c434
 F Makefile.msc bb4d970894abbbe0e88d00aac29bd52af8bc95f4
@@ -330,8 +330,8 @@ F src/auth.c 930b376a9c56998557367e6f7f8aaeac82a2a792
 F src/backup.c faf17e60b43233c214aae6a8179d24503a61e83b
 F src/bitvec.c 3ee4c8b2c94ed3a7377256e18199e6ff5cf33f63
 F src/btmutex.c bc87dd3b062cc26edfe79918de2200ccb8d41e73
-F src/btree.c cfe038d1844420caddfa0238d52b7b2102dda98b
-F src/btree.h 630303068c82a359f6ddf202b205ae927721b090
+F src/btree.c a7ed407f879be72c94b81f965d552e51b54a971f
+F src/btree.h 01ec45846fa177e929f01ee36a8e34337d653544
 F src/btreeInt.h c18b7d2a3494695133e4e60ee36061d37f45d9a5
 F src/build.c 178f16698cbcb43402c343a9413fe22c99ffee21
 F src/callback.c 2e76147783386374bf01b227f752c81ec872d730
@@ -454,7 +454,7 @@ F src/update.c bb9854778bdbbbca55d7533e55058733bd3fefe3
 F src/utf.c 699001c79f28e48e9bcdf8a463da029ea660540c
 F src/util.c 3e2da6101888d073e79ecc6af5e0a2f70fa1e498
 F src/vacuum.c 33c174b28886b2faf26e503b5a49a1c01a9b1c16
-F src/vdbe.c f1a8e5bf7747f2e731812804cb65d4d07d86862e
+F src/vdbe.c e76ee960a2e6d099838173599ae2d0999dc3aa63
 F src/vdbe.h c044be7050ac6bf596eecc6ab159f5dbc020a3b7
 F src/vdbeInt.h 29b25318a0286c4b2599c0fbef6acf524398489a
 F src/vdbeapi.c 97129bec6b1553da50d8e73f523c278bda66d9f6
@@ -1534,7 +1534,7 @@ F vsixtest/vsixtest.tcl 6a9a6ab600c25a91a7acc6293828957a386a8a93
 F vsixtest/vsixtest.vcxproj.data 2ed517e100c66dc455b492e1a33350c1b20fbcdc
 F vsixtest/vsixtest.vcxproj.filters 37e51ffedcdb064aad6ff33b6148725226cd608e
 F vsixtest/vsixtest_TemporaryKey.pfx e5b1b036facdb453873e7084e1cae9102ccc67a0
-P 03f75a67c320f21192d721a8c34d49dea48ffdbb
-R 8e81a23a0b0c79dacc7554a88cc14173
+P 5ed0bd387699a0f3b477d4f3cfcb460a6a44cb84
+R 666875522a5a69f5f9bb179805474981
 U drh
-Z deb6f2821ede2b99520e7ac64aa770e4
+Z 3c6d6cf804e5301c81a1f9af34f5b4ed

manifest.uuid

@@ -1 +1 @@
-5ed0bd387699a0f3b477d4f3cfcb460a6a44cb84
+663473850c4274270445b3771911fa773a8c405f

src/btree.c

@@ -4278,6 +4278,10 @@ int sqlite3BtreeCursorIsValid(BtCursor *pCur){
   return pCur && pCur->eState==CURSOR_VALID;
 }
 #endif /* NDEBUG */
+int sqlite3BtreeCursorIsValidNN(BtCursor *pCur){
+  assert( pCur!=0 );
+  return pCur->eState==CURSOR_VALID;
+}
 
 /*
 ** Return the value of the integer key or "rowid" for a table btree.

src/btree.h

@@ -310,6 +310,7 @@ int sqlite3HeaderSizeBtree(void);
 #ifndef NDEBUG
 int sqlite3BtreeCursorIsValid(BtCursor*);
 #endif
+int sqlite3BtreeCursorIsValidNN(BtCursor*);
 
 #ifndef SQLITE_OMIT_BTREECOUNT
 int sqlite3BtreeCount(BtCursor *, i64 *);

src/vdbe.c

@@ -4799,6 +4799,13 @@ case OP_NullRow: {
 ** This opcode leaves the cursor configured to move in reverse order,
 ** from the end toward the beginning.  In other words, the cursor is
 ** configured to use Prev, not Next.
+**
+** If P3 is -1, then the cursor is positioned at the end of the btree
+** for the purpose of appending a new entry onto the btree.  In that
+** case P2 must be 0.  It is assumed that the cursor is used only for
+** appending and so if the cursor is valid, then the cursor must already
+** be pointing at the end of the btree and so no changes are made to
+** the cursor.
 */
 case OP_Last: {        /* jump */
   VdbeCursor *pC;
@@ -4812,18 +4819,22 @@ case OP_Last: {        /* jump */
   pCrsr = pC->uc.pCursor;
   res = 0;
   assert( pCrsr!=0 );
-  rc = sqlite3BtreeLast(pCrsr, &res);
-  pC->nullRow = (u8)res;
-  pC->deferredMoveto = 0;
-  pC->cacheStatus = CACHE_STALE;
   pC->seekResult = pOp->p3;
 #ifdef SQLITE_DEBUG
   pC->seekOp = OP_Last;
 #endif
-  if( rc ) goto abort_due_to_error;
-  if( pOp->p2>0 ){
-    VdbeBranchTaken(res!=0,2);
-    if( res ) goto jump_to_p2;
+  if( pOp->p3==0 || !sqlite3BtreeCursorIsValidNN(pCrsr) ){
+    rc = sqlite3BtreeLast(pCrsr, &res);
+    pC->nullRow = (u8)res;
+    pC->deferredMoveto = 0;
+    pC->cacheStatus = CACHE_STALE;
+    if( rc ) goto abort_due_to_error;
+    if( pOp->p2>0 ){
+      VdbeBranchTaken(res!=0,2);
+      if( res ) goto jump_to_p2;
+    }
+  }else{
+    assert( pOp->p2==0 );
   }
   break;
 }