Simplified experimental changes to promote the use of co-routines. Less

cruft than the coroutines-exp1 branch, but still does not work.  Checked in
as a work-in-progress.

FossilOrigin-Name: e2318a30bf6ad2aeb4c4cb29661bc24ff78eb51bf07decc4b8da1ecac0015ef0

manifest

@@ -1,5 +1,5 @@
-C Fix\scompiler\swarnings\sin\sthe\snew\sdynamic\scontinuation\sprompt\slogic\sof\nthe\sCLI.
+C Simplified\sexperimental\schanges\sto\spromote\sthe\suse\sof\sco-routines.\s\sLess\ncruft\sthan\sthe\scoroutines-exp1\sbranch,\sbut\sstill\sdoes\snot\swork.\s\sChecked\sin\nas\sa\swork-in-progress.
-D 2022-12-06T15:11:13.637
+D 2022-12-06T15:24:05.905
 F .fossil-settings/empty-dirs dbb81e8fc0401ac46a1491ab34a7f2c7c0452f2f06b54ebb845d024ca8283ef1
 F .fossil-settings/ignore-glob 35175cdfcf539b2318cb04a9901442804be81cd677d8b889fcc9149c21f239ea
 F LICENSE.md df5091916dbb40e6e9686186587125e1b2ff51f022cc334e886c19a0e9982724
@@ -645,12 +645,12 @@ F src/printf.c e99ee9741e79ae3873458146f59644276657340385ade4e76a5f5d1c25793764
 F src/random.c 606b00941a1d7dd09c381d3279a058d771f406c5213c9932bbd93d5587be4b9c
 F src/resolve.c efea4e5fbecfd6d0a9071b0be0d952620991673391b6ffaaf4c277b0bb674633
 F src/rowset.c ba9515a922af32abe1f7d39406b9d35730ed65efab9443dc5702693b60854c92
-F src/select.c 56162cde2f71314826f831618eae853205628080afa25cd90faef7a9b761dee4
+F src/select.c cbb0ce95039273f436cdad9308251ab3affd69482fd9927495e1c37875afeeb1
 F src/shell.c.in f37273af2d5cd2299091b3c1e260254ebd7cd16d7602426983b36009290e8577
 F src/sqlite.h.in 1fe1836879ecbb2e28f00f44eb6092db09a2a06bf072af351c6c2466bd515496
 F src/sqlite3.rc 5121c9e10c3964d5755191c80dd1180c122fc3a8
 F src/sqlite3ext.h c4b9fa7a7e2bcdf850cfeb4b8a91d5ec47b7a00033bc996fd2ee96cbf2741f5f
-F src/sqliteInt.h 0c9934acd88e0fa14f0d4743233b4cd7bd7bbc84099ba3cad50d8e69676ce2b9
+F src/sqliteInt.h 5a91a427ab821dd3db556411ec0bf0f02bea796ce9927183979c2a1954ae4630
 F src/sqliteLimit.h d7323ffea5208c6af2734574bae933ca8ed2ab728083caa117c9738581a31657
 F src/status.c 160c445d7d28c984a0eae38c144f6419311ed3eace59b44ac6dafc20db4af749
 F src/table.c 0f141b58a16de7e2fbe81c308379e7279f4c6b50eb08efeec5892794a0ba30d1
@@ -712,13 +712,13 @@ F src/threads.c 4ae07fa022a3dc7c5beb373cf744a85d3c5c6c3c
 F src/tokenize.c 1305797eab3542a0896b552c6e7669c972c1468e11e92b370533c1f37a37082b
 F src/treeview.c 29b1dc7e0f84ba090734febe27393d4719682af0cae1b902d5ebf0236ecebea4
 F src/trigger.c 5e68b790f022b8dafbfb0eb244786512a95c9575fc198719d2557d73e5795858
-F src/update.c 5b0302c47cf31b533d5dff04c497ca1d8b9d89c39727e633fbe7b882fd5ac5aa
+F src/update.c 3cf1cb45674177e09338bdbe5454fb62207c7f2eb8cea288e74286467e901959
 F src/upsert.c 5303dc6c518fa7d4b280ec65170f465c7a70b7ac2b22491598f6d0b4875b3145
 F src/utf.c ee39565f0843775cc2c81135751ddd93eceb91a673ea2c57f61c76f288b041a0
 F src/util.c 313f3154e2b85a447326f5dd15de8d31a4df6ab0c3579bd58f426ff634ec9050
 F src/vacuum.c 84ce7f01f8a7a08748e107a441db83bcec13970190ddcb0c9ff522adbc1c23fd
 F src/vdbe.c e744259050ec9bbcd47acf9a03a66fe3305d7429c823995de11ed524ca06d16f
-F src/vdbe.h 6d921884cf8ec6a53efba99f8b68e32e955367631743e29039840e781aaf547c
+F src/vdbe.h c93d4bc242fc9109558aa6b3ce8acef7effe100a42c148dc63239c488ad6c060
 F src/vdbeInt.h e83be1eea422758d42302941e96e59d93193c373da655a87befdc03a851e0f95
 F src/vdbeapi.c 959cef4c1e5cb6589e67b3295fe9d3e45cbd109ae6618d57b74c900dbd6be0cd
 F src/vdbeaux.c 0b81f317c86ed9f4ba822af66a52777fed6e8180edc79d4fc62ffe75c8e52d80
@@ -2067,8 +2067,11 @@ F vsixtest/vsixtest.tcl 6a9a6ab600c25a91a7acc6293828957a386a8a93
 F vsixtest/vsixtest.vcxproj.data 2ed517e100c66dc455b492e1a33350c1b20fbcdc
 F vsixtest/vsixtest.vcxproj.filters 37e51ffedcdb064aad6ff33b6148725226cd608e
 F vsixtest/vsixtest_TemporaryKey.pfx e5b1b036facdb453873e7084e1cae9102ccc67a0
-P c0cfe0582add87981826d124a0763482f51fae4b105b5a970dd56919f1d04d60
+P 0d80500d358fa1c9b5867c2c8250d278ba813bf2ad81bb0bc3f820a71489b374
-R 19f4ce887fdd7ce982932018e71e1a9d
+R da3604bd27058bf7971e3104c707bf9f
+T *branch * coroutines-exp2
+T *sym-coroutines-exp2 *
+T -sym-trunk *
 U drh
-Z 087fdbe4ee41c07ef7676876e727f795
+Z 83efea07fbf822c79733971b25cfb62c
 # Remove this line to create a well-formed Fossil manifest.

manifest.uuid

@@ -1 +1 @@
-0d80500d358fa1c9b5867c2c8250d278ba813bf2ad81bb0bc3f820a71489b374
+e2318a30bf6ad2aeb4c4cb29661bc24ff78eb51bf07decc4b8da1ecac0015ef0

src/select.c

@@ -6854,6 +6854,52 @@ static int sameSrcAlias(SrcItem *p0, SrcList *pSrc){
   return 0;
 }
 
+/*
+** Return TRUE (non-zero) if the i-th entry in the pTabList SrcList can
+** be implemented as a co-routine.  The i-th entry is guaranteed to be
+** a subquery.
+**
+** The subquery is implemented as a co-routine if all of the following are
+** true:
+**
+**    (1)  Either of the following are true:
+**         (1a)  The subquery must be the outer loop because it is either
+**               (i) the only term in the FROM clause, or because (ii) it
+**               is the left-most term and a CROSS JOIN or similar requires
+**               it to be the outer loop. subquery and there is nothing
+**         (1b)  There is nothing that would prevent the subquery from
+**               being an outer loop and the SQLITE_PREPARE_SAFESQL flag
+**               is not set.
+**    (2)  The subquery is not a CTE that should be materialized
+**    (3)  The subquery is not part of a left operand for a RIGHT JOIN
+**    (4)  The SQLITE_Coroutine optimization disable flag is not set
+*/
+static int fromClauseTermCanBeCoroutine(
+  Parse *pParse,            /* Parsing context */
+  SrcList *pTabList,        /* FROM clause */
+  int i                     /* Which term of the FROM clause */
+){
+  SrcItem *pItem = &pTabList->a[i];
+  if( pItem->fg.isCte && pItem->u2.pCteUse->eM10d==M10d_Yes ) return 0;/* (2) */
+  if( pTabList->a[0].fg.jointype & JT_LTORJ ) return 0;                /* (3) */
+  if( OptimizationDisabled(pParse->db, SQLITE_Coroutines) ) return 0;  /* (4) */
+  if( i==0 ){
+    if( pTabList->nSrc==1 ) return 1;                              /* (1a-i) */
+    if( pTabList->a[1].fg.jointype & JT_CROSS ) return 1;          /* (1a-ii) */
+    if( pParse->prepFlags & SQLITE_PREPARE_SAFEOPT ) return 0;     
+    return 1;
+  }
+  if( pParse->prepFlags & SQLITE_PREPARE_SAFEOPT ) return 0;
+  while( 1 /*exit-by-break*/ ){
+    if( pItem->fg.jointype & (JT_OUTER|JT_CROSS)  ) return 0;
+    if( i==0 ) break;
+    i--;
+    pItem--;
+    if( pItem->pSelect!=0 ) return 0;
+  }
+  return 1;
+}
+
 /*
 ** Generate code for the SELECT statement given in the p argument.  
 **
@@ -7241,35 +7287,19 @@ int sqlite3Select(
     pParse->zAuthContext = pItem->zName;
 
     /* Generate code to implement the subquery
-    **
-    ** The subquery is implemented as a co-routine if all of the following are
-    ** true:
-    **
-    **    (1)  the subquery is guaranteed to be the outer loop (so that
-    **         it does not need to be computed more than once), and
-    **    (2)  the subquery is not a CTE that should be materialized
-    **    (3)  the subquery is not part of a left operand for a RIGHT JOIN
     */
-    if( i==0
+    if( fromClauseTermCanBeCoroutine(pParse, pTabList, i) ){
-     && (pTabList->nSrc==1
-            || (pTabList->a[1].fg.jointype&(JT_OUTER|JT_CROSS))!=0)  /* (1) */
-     && (pItem->fg.isCte==0 || pItem->u2.pCteUse->eM10d!=M10d_Yes)   /* (2) */
-     && (pTabList->a[0].fg.jointype & JT_LTORJ)==0                   /* (3) */
-    ){
       /* Implement a co-routine that will return a single row of the result
       ** set on each invocation.
       */
       int addrTop = sqlite3VdbeCurrentAddr(v)+1;
-#ifdef SQLITE_ENABLE_STMT_SCANSTATUS
-      int addrExplain;
-#endif
      
       pItem->regReturn = ++pParse->nMem;
       sqlite3VdbeAddOp3(v, OP_InitCoroutine, pItem->regReturn, 0, addrTop);
       VdbeComment((v, "%!S", pItem));
       pItem->addrFillSub = addrTop;
       sqlite3SelectDestInit(&dest, SRT_Coroutine, pItem->regReturn);
-      ExplainQueryPlan2(addrExplain, (pParse, 1, "CO-ROUTINE %!S", pItem));
+      ExplainQueryPlan((pParse, 1, "CO-ROUTINE %!S", pItem));
       sqlite3Select(pParse, pSub, &dest);
       pItem->pTab->nRowLogEst = pSub->nSelectRow;
       pItem->fg.viaCoroutine = 1;
@@ -7277,10 +7307,6 @@ int sqlite3Select(
       sqlite3VdbeEndCoroutine(v, pItem->regReturn);
       sqlite3VdbeJumpHere(v, addrTop-1);
       sqlite3ClearTempRegCache(pParse);
-      /* For SQLITE_SCANSTAT_NCYCLE, all instructions from the 
-      ** OP_InitCoroutine coded above until this point are attributed to 
-      ** the CO-ROUTINE query element.  */
-      sqlite3VdbeScanStatusRange(v, addrExplain, addrExplain-1, -1);
     }else if( pItem->fg.isCte && pItem->u2.pCteUse->addrM9e>0 ){
       /* This is a CTE for which materialization code has already been
       ** generated.  Invoke the subroutine to compute the materialization,
@@ -7335,6 +7361,7 @@ int sqlite3Select(
       if( onceAddr ) sqlite3VdbeJumpHere(v, onceAddr);
       sqlite3VdbeAddOp2(v, OP_Return, pItem->regReturn, topAddr+1);
       VdbeComment((v, "end %!S", pItem));
+      sqlite3VdbeScanStatusRange(v, addrExplain, addrExplain, -1);
       sqlite3VdbeJumpHere(v, topAddr);
       sqlite3ClearTempRegCache(pParse);
       if( pItem->fg.isCte && pItem->fg.isCorrelated==0 ){
@@ -7344,9 +7371,6 @@ int sqlite3Select(
         pCteUse->iCur = pItem->iCursor;
         pCteUse->nRowEst = pSub->nSelectRow;
       }
-      /* For SQLITE_SCANSTAT_NCYCLE, all instructions from the 
-      ** OP_Explain to here are attibuted to the MATERIALIZE element. */
-      sqlite3VdbeScanStatusRange(v, addrExplain, addrExplain, -1);
     }
     if( db->mallocFailed ) goto select_end;
     pParse->nHeight -= sqlite3SelectExprHeight(p);

src/sqliteInt.h

@@ -1844,6 +1844,7 @@ struct sqlite3 {
 #define SQLITE_FlttnUnionAll  0x00800000 /* Disable the UNION ALL flattener */
    /* TH3 expects this value  ^^^^^^^^^^ See flatten04.test */
 #define SQLITE_IndexedExpr    0x01000000 /* Pull exprs from index when able */
+#define SQLITE_Coroutines     0x02000000 /* Co-routines for subqueries */
 #define SQLITE_AllOpts        0xffffffff /* All optimizations */
 
 /*

src/update.c

@@ -268,6 +268,7 @@ static void updateFromSelect(
   if( pSelect ) pSelect->selFlags |= SF_OrderByReqd;
   sqlite3SelectDestInit(&dest, eDest, iEph);
   dest.iSDParm2 = (pPk ? pPk->nKeyCol : -1);
+  pParse->prepFlags |= SQLITE_PREPARE_SAFEOPT;
   sqlite3Select(pParse, pSelect, &dest);
   sqlite3SelectDelete(db, pSelect);
 }

src/vdbe.h

@@ -165,6 +165,7 @@ typedef struct VdbeOpList VdbeOpList;
 ** Additional non-public SQLITE_PREPARE_* flags
 */
 #define SQLITE_PREPARE_SAVESQL  0x80  /* Preserve SQL text */
+#define SQLITE_PREPARE_SAFEOPT  0x40  /* Use only safe optimizations */
 #define SQLITE_PREPARE_MASK     0x0f  /* Mask of public flags */
 
 /*