Add opcodes OP_InitCoroutine and OP_EndCoroutine. Use these to remove the

need for separate boolean registers to record when a co-routine has finished.

FossilOrigin-Name: 5a88b6a7aef3a0d5380e19eee2ee38439cc9b08b

7 files changed, 107 insertions, 126 deletions

diff --git a/src/insert.c b/src/insert.c
index a2366360c..5dbdf9108 100644
--- a/src/insert.c
+++ b/src/insert.c
@@ -349,17 +349,13 @@ void sqlite3AutoincrementEnd(Parse *pParse){
 **                       co-routine.  Run the co-routine to its next breakpoint
 **                       by calling "OP_Yield $X" where $X is pDest->iSDParm.
 **
-**   pDest->iSDParm+1    The register holding the "completed" flag for the
-**                       co-routine. This register is 0 if the previous Yield
-**                       generated a new result row, or 1 if the subquery
-**                       has completed.  If the Yield is called again
-**                       after this register becomes 1, then the VDBE will
-**                       halt with an SQLITE_INTERNAL error.
-**
 **   pDest->iSdst        First result register.
 **
 **   pDest->nSdst        Number of result registers.
 **
+** At EOF the first result register will be marked as "undefined" so that
+** the caller can know when to stop reading results.
+**
 ** This routine handles all of the register allocation and fills in the
 ** pDest structure appropriately.
 **
@@ -370,7 +366,6 @@ void sqlite3AutoincrementEnd(Parse *pParse){
 ** reg[pDest->iSdst+pDest->nSdst-1]:
 **
 **         X <- A
-**         EOF <- 0
 **         goto B
 **      A: setup for the SELECT
 **         loop rows in the SELECT
@@ -378,16 +373,13 @@ void sqlite3AutoincrementEnd(Parse *pParse){
 **           yield X
 **         end loop
 **         cleanup after the SELECT
-**         EOF <- 1
-**         yield X
-**         halt-error
+**         end co-routine R
 **      B:
 **
 ** To use this subroutine, the caller generates code as follows:
 **
 **         [ Co-routine generated by this subroutine, shown above ]
-**      S: yield X
-**         if EOF goto E
+**      S: yield X, at EOF goto E
 **         if skip this row, goto C
 **         if terminate loop, goto E
 **         deal with this row
@@ -396,31 +388,21 @@ void sqlite3AutoincrementEnd(Parse *pParse){
 */
 int sqlite3CodeCoroutine(Parse *pParse, Select *pSelect, SelectDest *pDest){
   int regYield;       /* Register holding co-routine entry-point */
-  int regEof;         /* Register holding co-routine completion flag */
   int addrTop;        /* Top of the co-routine */
-  int j1;             /* Jump instruction */
   int rc;             /* Result code */
   Vdbe *v;            /* VDBE under construction */
 
   regYield = ++pParse->nMem;
-  regEof = ++pParse->nMem;
   v = sqlite3GetVdbe(pParse);
-  addrTop = sqlite3VdbeCurrentAddr(v);
-  sqlite3VdbeAddOp2(v, OP_Integer, addrTop+2, regYield); /* X <- A */
-  VdbeComment((v, "Co-routine entry point"));
-  sqlite3VdbeAddOp2(v, OP_Integer, 0, regEof);           /* EOF <- 0 */
-  VdbeComment((v, "Co-routine completion flag"));
+  addrTop = sqlite3VdbeCurrentAddr(v) + 1;
+  sqlite3VdbeAddOp3(v, OP_InitCoroutine, regYield, 0, addrTop);
   sqlite3SelectDestInit(pDest, SRT_Coroutine, regYield);
-  j1 = sqlite3VdbeAddOp2(v, OP_Goto, 0, 0);
   rc = sqlite3Select(pParse, pSelect, pDest);
   assert( pParse->nErr==0 || rc );
   if( pParse->db->mallocFailed && rc==SQLITE_OK ) rc = SQLITE_NOMEM;
   if( rc ) return rc;
-  sqlite3VdbeAddOp2(v, OP_Integer, 1, regEof);            /* EOF <- 1 */
-  sqlite3VdbeAddOp1(v, OP_Yield, regYield);   /* yield X */
-  sqlite3VdbeAddOp2(v, OP_Halt, SQLITE_INTERNAL, OE_Abort);
-  VdbeComment((v, "End of coroutine"));
-  sqlite3VdbeJumpHere(v, j1);                             /* label B: */
+  sqlite3VdbeAddOp1(v, OP_EndCoroutine, regYield);
+  sqlite3VdbeJumpHere(v, addrTop - 1);                       /* label B: */
   return rc;
 }
 
@@ -488,7 +470,6 @@ static int xferOptimization(
 ** and the SELECT clause does not read from <table> at any time.
 ** The generated code follows this template:
 **
-**         EOF <- 0
 **         X <- A
 **         goto B
 **      A: setup for the SELECT
@@ -497,12 +478,9 @@ static int xferOptimization(
 **           yield X
 **         end loop
 **         cleanup after the SELECT
-**         EOF <- 1
-**         yield X
-**         goto A
+**         end-coroutine X
 **      B: open write cursor to <table> and its indices
-**      C: yield X
-**         if EOF goto D
+**      C: yield X, at EOF goto D
 **         insert the select result into <table> from R..R+n
 **         goto C
 **      D: cleanup
@@ -513,7 +491,6 @@ static int xferOptimization(
 ** we have to use a intermediate table to store the results of
 ** the select.  The template is like this:
 **
-**         EOF <- 0
 **         X <- A
 **         goto B
 **      A: setup for the SELECT
@@ -522,12 +499,9 @@ static int xferOptimization(
 **           yield X
 **         end loop
 **         cleanup after the SELECT
-**         EOF <- 1
-**         yield X
-**         halt-error
+**         end co-routine R
 **      B: open temp table
-**      L: yield X
-**         if EOF goto M
+**      L: yield X, at EOF goto M
 **         insert row from R..R+n into temp table
 **         goto L
 **      M: open write cursor to <table> and its indices
@@ -576,7 +550,6 @@ void sqlite3Insert(
   int regIns;           /* Block of regs holding rowid+data being inserted */
   int regRowid;         /* registers holding insert rowid */
   int regData;          /* register holding first column to insert */
-  int regEof = 0;       /* Register recording end of SELECT data */
   int *aRegIdx = 0;     /* One register allocated to each index */
 
 #ifndef SQLITE_OMIT_TRIGGER
@@ -689,7 +662,6 @@ void sqlite3Insert(
     int rc = sqlite3CodeCoroutine(pParse, pSelect, &dest);
     if( rc ) goto insert_cleanup;
 
-    regEof = dest.iSDParm + 1;
     regFromSelect = dest.iSdst;
     assert( pSelect->pEList );
     nColumn = pSelect->pEList->nExpr;
@@ -714,8 +686,7 @@ void sqlite3Insert(
       ** here is from the 4th template:
       **
       **      B: open temp table
-      **      L: yield X
-      **         if EOF goto M
+      **      L: yield X, goto M at EOF
       **         insert row from R..R+n into temp table
       **         goto L
       **      M: ...
@@ -723,19 +694,17 @@ void sqlite3Insert(
       int regRec;          /* Register to hold packed record */
       int regTempRowid;    /* Register to hold temp table ROWID */
       int addrTop;         /* Label "L" */
-      int addrIf;          /* Address of jump to M */
 
       srcTab = pParse->nTab++;
       regRec = sqlite3GetTempReg(pParse);
       regTempRowid = sqlite3GetTempReg(pParse);
       sqlite3VdbeAddOp2(v, OP_OpenEphemeral, srcTab, nColumn);
       addrTop = sqlite3VdbeAddOp1(v, OP_Yield, dest.iSDParm);
-      addrIf = sqlite3VdbeAddOp1(v, OP_If, regEof);
       sqlite3VdbeAddOp3(v, OP_MakeRecord, regFromSelect, nColumn, regRec);
       sqlite3VdbeAddOp2(v, OP_NewRowid, srcTab, regTempRowid);
       sqlite3VdbeAddOp3(v, OP_Insert, srcTab, regRec, regTempRowid);
       sqlite3VdbeAddOp2(v, OP_Goto, 0, addrTop);
-      sqlite3VdbeJumpHere(v, addrIf);
+      sqlite3VdbeJumpHere(v, addrTop);
       sqlite3ReleaseTempReg(pParse, regRec);
       sqlite3ReleaseTempReg(pParse, regTempRowid);
     }
@@ -847,7 +816,7 @@ void sqlite3Insert(
     /* This block codes the top of loop only.  The complete loop is the
     ** following pseudocode (template 4):
     **
-    **         rewind temp table
+    **         rewind temp table, if empty goto D
     **      C: loop over rows of intermediate table
     **           transfer values form intermediate table into <table>
     **         end loop
@@ -859,14 +828,12 @@ void sqlite3Insert(
     /* This block codes the top of loop only.  The complete loop is the
     ** following pseudocode (template 3):
     **
-    **      C: yield X
-    **         if EOF goto D
+    **      C: yield X, at EOF goto D
     **         insert the select result into <table> from R..R+n
     **         goto C
     **      D: ...
     */
-    addrCont = sqlite3VdbeAddOp1(v, OP_Yield, dest.iSDParm);
-    addrInsTop = sqlite3VdbeAddOp1(v, OP_If, regEof);
+    addrInsTop = addrCont = sqlite3VdbeAddOp1(v, OP_Yield, dest.iSDParm);
   }
 
   /* Allocate registers for holding the rowid of the new row,
diff --git a/src/select.c b/src/select.c
index f923766c8..c0728f887 100644
--- a/src/select.c
+++ b/src/select.c
@@ -765,12 +765,8 @@ static void selectInnerLoop(
     }
 #endif /* #ifndef SQLITE_OMIT_SUBQUERY */
 
-    /* Send the data to the callback function or to a subroutine.  In the
-    ** case of a subroutine, the subroutine itself is responsible for
-    ** popping the data from the stack.
-    */
-    case SRT_Coroutine:
-    case SRT_Output: {
+    case SRT_Coroutine:       /* Send data to a co-routine */
+    case SRT_Output: {        /* Return the results */
       testcase( eDest==SRT_Coroutine );
       testcase( eDest==SRT_Output );
       if( pOrderBy ){
@@ -2572,9 +2568,7 @@ static int multiSelectOrderBy(
   SelectDest destA;     /* Destination for coroutine A */
   SelectDest destB;     /* Destination for coroutine B */
   int regAddrA;         /* Address register for select-A coroutine */
-  int regEofA;          /* Flag to indicate when select-A is complete */
   int regAddrB;         /* Address register for select-B coroutine */
-  int regEofB;          /* Flag to indicate when select-B is complete */
   int addrSelectA;      /* Address of the select-A coroutine */
   int addrSelectB;      /* Address of the select-B coroutine */
   int regOutA;          /* Address register for the output-A subroutine */
@@ -2582,6 +2576,7 @@ static int multiSelectOrderBy(
   int addrOutA;         /* Address of the output-A subroutine */
   int addrOutB = 0;     /* Address of the output-B subroutine */
   int addrEofA;         /* Address of the select-A-exhausted subroutine */
+  int addrEofA_noB;     /* Alternate addrEofA if B is uninitialized */
   int addrEofB;         /* Address of the select-B-exhausted subroutine */
   int addrAltB;         /* Address of the A<B subroutine */
   int addrAeqB;         /* Address of the A==B subroutine */
@@ -2718,37 +2713,30 @@ static int multiSelectOrderBy(
   p->pOffset = 0;
 
   regAddrA = ++pParse->nMem;
-  regEofA = ++pParse->nMem;
   regAddrB = ++pParse->nMem;
-  regEofB = ++pParse->nMem;
   regOutA = ++pParse->nMem;
   regOutB = ++pParse->nMem;
   sqlite3SelectDestInit(&destA, SRT_Coroutine, regAddrA);
   sqlite3SelectDestInit(&destB, SRT_Coroutine, regAddrB);
 
-  /* Jump past the various subroutines and coroutines to the main
-  ** merge loop
-  */
-  j1 = sqlite3VdbeAddOp0(v, OP_Goto);
-  addrSelectA = sqlite3VdbeCurrentAddr(v);
-
-
   /* Generate a coroutine to evaluate the SELECT statement to the
   ** left of the compound operator - the "A" select.
   */
-  VdbeNoopComment((v, "Begin coroutine for left SELECT"));
+  addrSelectA = sqlite3VdbeCurrentAddr(v) + 1;
+  j1 = sqlite3VdbeAddOp3(v, OP_InitCoroutine, regAddrA, 0, addrSelectA);
+  VdbeComment((v, "left SELECT"));
   pPrior->iLimit = regLimitA;
   explainSetInteger(iSub1, pParse->iNextSelectId);
   sqlite3Select(pParse, pPrior, &destA);
-  sqlite3VdbeAddOp2(v, OP_Integer, 1, regEofA);
-  sqlite3VdbeAddOp1(v, OP_Yield, regAddrA);
-  VdbeNoopComment((v, "End coroutine for left SELECT"));
+  sqlite3VdbeAddOp1(v, OP_EndCoroutine, regAddrA);
+  sqlite3VdbeJumpHere(v, j1);
 
   /* Generate a coroutine to evaluate the SELECT statement on 
   ** the right - the "B" select
   */
-  addrSelectB = sqlite3VdbeCurrentAddr(v);
-  VdbeNoopComment((v, "Begin coroutine for right SELECT"));
+  addrSelectB = sqlite3VdbeCurrentAddr(v) + 1;
+  j1 = sqlite3VdbeAddOp3(v, OP_InitCoroutine, regAddrB, 0, addrSelectB);
+  VdbeComment((v, "right SELECT"));
   savedLimit = p->iLimit;
   savedOffset = p->iOffset;
   p->iLimit = regLimitB;
@@ -2757,9 +2745,7 @@ static int multiSelectOrderBy(
   sqlite3Select(pParse, p, &destB);
   p->iLimit = savedLimit;
   p->iOffset = savedOffset;
-  sqlite3VdbeAddOp2(v, OP_Integer, 1, regEofB);
-  sqlite3VdbeAddOp1(v, OP_Yield, regAddrB);
-  VdbeNoopComment((v, "End coroutine for right SELECT"));
+  sqlite3VdbeAddOp1(v, OP_EndCoroutine, regAddrB);
 
   /* Generate a subroutine that outputs the current row of the A
   ** select as the next output row of the compound select.
@@ -2783,13 +2769,12 @@ static int multiSelectOrderBy(
   /* Generate a subroutine to run when the results from select A
   ** are exhausted and only data in select B remains.
   */
-  VdbeNoopComment((v, "eof-A subroutine"));
   if( op==TK_EXCEPT || op==TK_INTERSECT ){
-    addrEofA = sqlite3VdbeAddOp2(v, OP_Goto, 0, labelEnd);
+    addrEofA_noB = addrEofA = labelEnd;
   }else{  
-    addrEofA = sqlite3VdbeAddOp2(v, OP_If, regEofB, labelEnd);
-    sqlite3VdbeAddOp2(v, OP_Gosub, regOutB, addrOutB);
-    sqlite3VdbeAddOp1(v, OP_Yield, regAddrB);
+    VdbeNoopComment((v, "eof-A subroutine"));
+    addrEofA = sqlite3VdbeAddOp2(v, OP_Gosub, regOutB, addrOutB);
+    addrEofA_noB = sqlite3VdbeAddOp2(v, OP_Yield, regAddrB, labelEnd);
     sqlite3VdbeAddOp2(v, OP_Goto, 0, addrEofA);
     p->nSelectRow += pPrior->nSelectRow;
   }
@@ -2802,9 +2787,8 @@ static int multiSelectOrderBy(
     if( p->nSelectRow > pPrior->nSelectRow ) p->nSelectRow = pPrior->nSelectRow;
   }else{  
     VdbeNoopComment((v, "eof-B subroutine"));
-    addrEofB = sqlite3VdbeAddOp2(v, OP_If, regEofA, labelEnd);
-    sqlite3VdbeAddOp2(v, OP_Gosub, regOutA, addrOutA);
-    sqlite3VdbeAddOp1(v, OP_Yield, regAddrA);
+    addrEofB = sqlite3VdbeAddOp2(v, OP_Gosub, regOutA, addrOutA);
+    sqlite3VdbeAddOp2(v, OP_Yield, regAddrA, labelEnd);
     sqlite3VdbeAddOp2(v, OP_Goto, 0, addrEofB);
   }
 
@@ -2812,8 +2796,7 @@ static int multiSelectOrderBy(
   */
   VdbeNoopComment((v, "A-lt-B subroutine"));
   addrAltB = sqlite3VdbeAddOp2(v, OP_Gosub, regOutA, addrOutA);
-  sqlite3VdbeAddOp1(v, OP_Yield, regAddrA);
-  sqlite3VdbeAddOp2(v, OP_If, regEofA, addrEofA);
+  sqlite3VdbeAddOp2(v, OP_Yield, regAddrA, addrEofA);
   sqlite3VdbeAddOp2(v, OP_Goto, 0, labelCmpr);
 
   /* Generate code to handle the case of A==B
@@ -2826,8 +2809,7 @@ static int multiSelectOrderBy(
   }else{
     VdbeNoopComment((v, "A-eq-B subroutine"));
     addrAeqB =
-    sqlite3VdbeAddOp1(v, OP_Yield, regAddrA);
-    sqlite3VdbeAddOp2(v, OP_If, regEofA, addrEofA);
+    sqlite3VdbeAddOp2(v, OP_Yield, regAddrA, addrEofA);
     sqlite3VdbeAddOp2(v, OP_Goto, 0, labelCmpr);
   }
 
@@ -2838,19 +2820,14 @@ static int multiSelectOrderBy(
   if( op==TK_ALL || op==TK_UNION ){
     sqlite3VdbeAddOp2(v, OP_Gosub, regOutB, addrOutB);
   }
-  sqlite3VdbeAddOp1(v, OP_Yield, regAddrB);
-  sqlite3VdbeAddOp2(v, OP_If, regEofB, addrEofB);
+  sqlite3VdbeAddOp2(v, OP_Yield, regAddrB, addrEofB);
   sqlite3VdbeAddOp2(v, OP_Goto, 0, labelCmpr);
 
   /* This code runs once to initialize everything.
   */
   sqlite3VdbeJumpHere(v, j1);
-  sqlite3VdbeAddOp2(v, OP_Integer, 0, regEofA);
-  sqlite3VdbeAddOp2(v, OP_Integer, 0, regEofB);
-  sqlite3VdbeAddOp2(v, OP_Gosub, regAddrA, addrSelectA);
-  sqlite3VdbeAddOp2(v, OP_Gosub, regAddrB, addrSelectB);
-  sqlite3VdbeAddOp2(v, OP_If, regEofA, addrEofA);
-  sqlite3VdbeAddOp2(v, OP_If, regEofB, addrEofB);
+  sqlite3VdbeAddOp2(v, OP_Yield, regAddrA, addrEofA_noB);
+  sqlite3VdbeAddOp2(v, OP_Yield, regAddrB, addrEofB);
 
   /* Implement the main merge loop
   */
@@ -4559,9 +4536,7 @@ int sqlite3Select(
       ** set on each invocation.
       */
       int addrTop;
-      int addrEof;
       pItem->regReturn = ++pParse->nMem;
-      addrEof = ++pParse->nMem;
       /* Before coding the OP_Goto to jump to the start of the main routine,
       ** ensure that the jump to the verify-schema routine has already
       ** been coded. Otherwise, the verify-schema would likely be coded as 
@@ -4574,10 +4549,8 @@ int sqlite3Select(
       sqlite3VdbeAddOp0(v, OP_Goto);
       addrTop = sqlite3VdbeAddOp1(v, OP_OpenPseudo, pItem->iCursor);
       sqlite3VdbeChangeP5(v, 1);
-      VdbeComment((v, "coroutine for %s", pItem->pTab->zName));
+      VdbeComment((v, "coroutine %s", pItem->pTab->zName));
       pItem->addrFillSub = addrTop;
-      sqlite3VdbeAddOp2(v, OP_Integer, 0, addrEof);
-      sqlite3VdbeChangeP5(v, 1);
       sqlite3SelectDestInit(&dest, SRT_Coroutine, pItem->regReturn);
       explainSetInteger(pItem->iSelectId, (u8)pParse->iNextSelectId);
       sqlite3Select(pParse, pSub, &dest);
@@ -4585,9 +4558,7 @@ int sqlite3Select(
       pItem->viaCoroutine = 1;
       sqlite3VdbeChangeP2(v, addrTop, dest.iSdst);
       sqlite3VdbeChangeP3(v, addrTop, dest.nSdst);
-      sqlite3VdbeAddOp2(v, OP_Integer, 1, addrEof);
-      sqlite3VdbeAddOp1(v, OP_Yield, pItem->regReturn);
-      VdbeComment((v, "end %s", pItem->pTab->zName));
+      sqlite3VdbeAddOp1(v, OP_EndCoroutine, pItem->regReturn);
       sqlite3VdbeJumpHere(v, addrTop-1);
       sqlite3ClearTempRegCache(pParse);
     }else{
diff --git a/src/vdbe.c b/src/vdbe.c
index 5816c4a79..8067f9a12 100644
--- a/src/vdbe.c
+++ b/src/vdbe.c
@@ -393,7 +393,7 @@ void sqlite3VdbeMemPrettyPrint(Mem *pMem, char *zBuf){
 ** Print the value of a register for tracing purposes:
 */
 static void memTracePrint(Mem *p){
-  if( p->flags & MEM_Invalid ){
+  if( p->flags & MEM_Undefined ){
     printf(" undefined");
   }else if( p->flags & MEM_Null ){
     printf(" NULL");
@@ -702,7 +702,6 @@ check_for_interrupt:
 }
 
 /* Opcode:  Gosub P1 P2 * * *
-** Synopsis:  r[P1]=pc; pc=P2
 **
 ** Write the current address onto register P1
 ** and then jump to address P2.
@@ -720,23 +719,67 @@ case OP_Gosub: {            /* jump */
 }
 
 /* Opcode:  Return P1 * * * *
-** Synopsis:  pc=r[P1]+1
 **
-** Jump to the next instruction after the address in register P1.
+** Jump to the next instruction after the address in register P1.  After
+** the jump, register P1 becomes undefined.
 */
 case OP_Return: {           /* in1 */
   pIn1 = &aMem[pOp->p1];
-  assert( pIn1->flags & MEM_Int );
+  assert( pIn1->flags==MEM_Int );
   pc = (int)pIn1->u.i;
+  pIn1->flags = MEM_Undefined;
   break;
 }
 
-/* Opcode:  Yield P1 * * * *
-** Synopsis: swap(pc,r[P1])
+/* Opcode: InitCoroutine P1 P2 P3 * *
+**
+** Set up register P1 so that it will OP_Yield to the co-routine
+** located at address P3.
+**
+** If P2!=0 then the co-routine implementation immediately follows
+** this opcode.  So jump over the co-routine implementation to
+** address P2.
+*/
+case OP_InitCoroutine: {     /* jump */
+  assert( pOp->p1>0 &&  pOp->p1<=(p->nMem-p->nCursor) );
+  assert( pOp->p2>=0 && pOp->p2<p->nOp );
+  assert( pOp->p3>=0 && pOp->p3<p->nOp );
+  pOut = &aMem[pOp->p1];
+  assert( !VdbeMemDynamic(pOut) );
+  pOut->u.i = pOp->p3 - 1;
+  pOut->flags = MEM_Int;
+  if( pOp->p2 ) pc = pOp->p2 - 1;
+  break;
+}
+
+/* Opcode:  EndCoroutine P1 * * * *
+**
+** The instruction at the address in register P1 is an OP_Yield.
+** Jump to the P2 parameter of that OP_Yield.
+** After the jump, register P1 becomes undefined.
+*/
+case OP_EndCoroutine: {           /* in1 */
+  VdbeOp *pCaller;
+  pIn1 = &aMem[pOp->p1];
+  assert( pIn1->flags==MEM_Int );
+  assert( pIn1->u.i>=0 && pIn1->u.i<p->nOp );
+  pCaller = &aOp[pIn1->u.i];
+  assert( pCaller->opcode==OP_Yield );
+  assert( pCaller->p2>=0 && pCaller->p2<p->nOp );
+  pc = pCaller->p2 - 1;
+  pIn1->flags = MEM_Undefined;
+  break;
+}
+
+/* Opcode:  Yield P1 P2 * * *
 **
 ** Swap the program counter with the value in register P1.
+**
+** If the co-routine ends with OP_Yield or OP_Return then continue
+** to the next instruction.  But if the co-routine ends with
+** OP_EndCoroutine, jump immediately to P2.
 */
-case OP_Yield: {            /* in1 */
+case OP_Yield: {            /* in1, jump */
   int pcDest;
   pIn1 = &aMem[pOp->p1];
   assert( (pIn1->flags & MEM_Dyn)==0 );
@@ -974,7 +1017,7 @@ case OP_Null: {           /* out2-prerelease */
 }
 
 
-/* Opcode: Blob P1 P2 * P4
+/* Opcode: Blob P1 P2 * P4 *
 ** Synopsis: r[P2]=P4 (len=P1)
 **
 ** P4 points to a blob of data P1 bytes long.  Store this
@@ -5191,7 +5234,7 @@ case OP_Program: {        /* jump */
 
     pEnd = &VdbeFrameMem(pFrame)[pFrame->nChildMem];
     for(pMem=VdbeFrameMem(pFrame); pMem!=pEnd; pMem++){
-      pMem->flags = MEM_Invalid;
+      pMem->flags = MEM_Undefined;
       pMem->db = db;
     }
   }else{
diff --git a/src/vdbeInt.h b/src/vdbeInt.h
index c4fa26cc0..f1d136a8e 100644
--- a/src/vdbeInt.h
+++ b/src/vdbeInt.h
@@ -198,7 +198,7 @@ struct Mem {
 #define MEM_Blob      0x0010   /* Value is a BLOB */
 #define MEM_RowSet    0x0020   /* Value is a RowSet object */
 #define MEM_Frame     0x0040   /* Value is a VdbeFrame object */
-#define MEM_Invalid   0x0080   /* Value is undefined */
+#define MEM_Undefined 0x0080   /* Value is undefined */
 #define MEM_Cleared   0x0100   /* NULL set by OP_Null, not from data */
 #define MEM_TypeMask  0x01ff   /* Mask of type bits */
 
@@ -230,7 +230,7 @@ struct Mem {
 ** is for use inside assert() statements only.
 */
 #ifdef SQLITE_DEBUG
-#define memIsValid(M)  ((M)->flags & MEM_Invalid)==0
+#define memIsValid(M)  ((M)->flags & MEM_Undefined)==0
 #endif
 
 /*
@@ -425,9 +425,10 @@ int sqlite3VdbeMemNumerify(Mem*);
 int sqlite3VdbeMemFromBtree(BtCursor*,u32,u32,int,Mem*);
 void sqlite3VdbeMemRelease(Mem *p);
 void sqlite3VdbeMemReleaseExternal(Mem *p);
+#define VdbeMemDynamic(X)  \
+  (((X)->flags&(MEM_Agg|MEM_Dyn|MEM_RowSet|MEM_Frame))!=0)
 #define VdbeMemRelease(X)  \
-  if((X)->flags&(MEM_Agg|MEM_Dyn|MEM_RowSet|MEM_Frame)) \
-    sqlite3VdbeMemReleaseExternal(X);
+  if( VdbeMemDynamic(X) ) sqlite3VdbeMemReleaseExternal(X);
 int sqlite3VdbeMemFinalize(Mem*, FuncDef*);
 const char *sqlite3OpcodeName(int);
 int sqlite3VdbeMemGrow(Mem *pMem, int n, int preserve);
diff --git a/src/vdbeaux.c b/src/vdbeaux.c
index 69611622a..59b766a79 100644
--- a/src/vdbeaux.c
+++ b/src/vdbeaux.c
@@ -1234,7 +1234,7 @@ static void releaseMemArray(Mem *p, int N){
         p->zMalloc = 0;
       }
 
-      p->flags = MEM_Invalid;
+      p->flags = MEM_Undefined;
     }
     db->mallocFailed = malloc_failed;
   }
@@ -1702,7 +1702,7 @@ void sqlite3VdbeMakeReady(
     p->aMem--;                      /* aMem[] goes from 1..nMem */
     p->nMem = nMem;                 /*       not from 0..nMem-1 */
     for(n=1; n<=nMem; n++){
-      p->aMem[n].flags = MEM_Invalid;
+      p->aMem[n].flags = MEM_Undefined;
       p->aMem[n].db = db;
     }
   }
@@ -1814,7 +1814,7 @@ static void Cleanup(Vdbe *p){
   int i;
   if( p->apCsr ) for(i=0; i<p->nCursor; i++) assert( p->apCsr[i]==0 );
   if( p->aMem ){
-    for(i=1; i<=p->nMem; i++) assert( p->aMem[i].flags==MEM_Invalid );
+    for(i=1; i<=p->nMem; i++) assert( p->aMem[i].flags==MEM_Undefined );
   }
 #endif
 
diff --git a/src/vdbemem.c b/src/vdbemem.c
index 9a621d1f7..982a44537 100644
--- a/src/vdbemem.c
+++ b/src/vdbemem.c
@@ -587,7 +587,7 @@ void sqlite3VdbeMemAboutToChange(Vdbe *pVdbe, Mem *pMem){
   Mem *pX;
   for(i=1, pX=&pVdbe->aMem[1]; i<=pVdbe->nMem; i++, pX++){
     if( pX->pScopyFrom==pMem ){
-      pX->flags |= MEM_Invalid;
+      pX->flags |= MEM_Undefined;
       pX->pScopyFrom = 0;
     }
   }
diff --git a/src/where.c b/src/where.c
index a900dd0b8..9abe3ad1c 100644
--- a/src/where.c
+++ b/src/where.c
@@ -2785,10 +2785,9 @@ static Bitmask codeOneLoopStart(
   /* Special case of a FROM clause subquery implemented as a co-routine */
   if( pTabItem->viaCoroutine ){
     int regYield = pTabItem->regReturn;
-    sqlite3VdbeAddOp2(v, OP_Integer, pTabItem->addrFillSub-1, regYield);
-    pLevel->p2 =  sqlite3VdbeAddOp1(v, OP_Yield, regYield);
+    sqlite3VdbeAddOp3(v, OP_InitCoroutine, regYield, 0, pTabItem->addrFillSub);
+    pLevel->p2 =  sqlite3VdbeAddOp2(v, OP_Yield, regYield, addrBrk);
     VdbeComment((v, "next row of co-routine %s", pTabItem->pTab->zName));
-    sqlite3VdbeAddOp2(v, OP_If, regYield+1, addrBrk);
     pLevel->op = OP_Goto;
   }else