From: drh <>
Date: Wed, 28 Jan 2026 16:59:34 +0000 (+0000)
Subject: Improved (faster) bytecode for the merge algorithm.
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=fabd481c76cc146d6de1352c25b6a2ddc5347c37;p=thirdparty%2Fsqlite.git

Improved (faster) bytecode for the merge algorithm.

FossilOrigin-Name: 0b7f4b97e68f17ae2fec86017cdb170f3b318a71cda34b5c82ec2d9df780564f
---

diff --git a/manifest b/manifest
index 0dad05dfe7..639d8f323d 100644
--- a/manifest
+++ b/manifest
@@ -1,5 +1,5 @@
-C Add\sa\scomment\sto\ssqlite3Stat4Value()\sexplaining\sthat\sit\sread\sa\sfew\sbytes\spast\sthe\send\sof\sthe\sspecified\sbuffer.
-D 2026-01-28T10:52:53.788
+C Improved\s(faster)\sbytecode\sfor\sthe\smerge\salgorithm.
+D 2026-01-28T16:59:34.852
 F .fossil-settings/binary-glob 61195414528fb3ea9693577e1980230d78a1f8b0a54c78cf1b9b24d0a409ed6a x
 F .fossil-settings/empty-dirs dbb81e8fc0401ac46a1491ab34a7f2c7c0452f2f06b54ebb845d024ca8283ef1
 F .fossil-settings/ignore-glob 35175cdfcf539b2318cb04a9901442804be81cd677d8b889fcc9149c21f239ea
@@ -738,7 +738,7 @@ F src/printf.c b1b29b5e58e1530d5daeee5963d3c318d8ab2d7e38437580e28755753e0c1ded
 F src/random.c 606b00941a1d7dd09c381d3279a058d771f406c5213c9932bbd93d5587be4b9c
 F src/resolve.c 47aa7fdc9ec4c19b103ac5e79d7887d30119b5675309facf5eed1118391c868b
 F src/rowset.c 8432130e6c344b3401a8874c3cb49fefe6873fec593294de077afea2dce5ec97
-F src/select.c 89db4768dc2ffed05755e072006dd13455cd387a2c169f167b48c1d48c56b257
+F src/select.c 4bee1bb231771e7c6e5aef243b1f74c3d330df5a005909d5e2c338fb1510fe55
 F src/shell.c.in d7c1041d6ad00bee2515842a1950640afe424df2e89ad2d6e3b9e68b184824a5
 F src/sqlite.h.in 8bcbaecfe2cbecf8c5c1381354fcdd7d307443e88b4953fccb222456c1267b61
 F src/sqlite3.rc 015537e6ac1eec6c7050e17b616c2ffe6f70fca241835a84a4f0d5937383c479
@@ -2193,8 +2193,8 @@ F tool/warnings-clang.sh bbf6a1e685e534c92ec2bfba5b1745f34fb6f0bc2a362850723a9ee
 F tool/warnings.sh d924598cf2f55a4ecbc2aeb055c10bd5f48114793e7ba25f9585435da29e7e98
 F tool/win/sqlite.vsix deb315d026cc8400325c5863eef847784a219a2f
 F tool/winmain.c 00c8fb88e365c9017db14c73d3c78af62194d9644feaf60e220ab0f411f3604c
-P 631c8d44cd1624ddc45babd3f0d810908c2a368784744262042c63506ff2e333
-R 9d3d16bae5779cc20645971566ff547b
-U dan
-Z 967d464084320ff484ef70ae7aceb51f
+P b95644eafdd42293096a3760af8b2110f3c7d83feecdeff5ff9f008d9748e874
+R e12fe81159464b3fa2ae49533a88f39a
+U drh
+Z 443016052e3b7e21943bf488170474d9
 # Remove this line to create a well-formed Fossil manifest.
diff --git a/manifest.uuid b/manifest.uuid
index bc6a27e457..c6a504886a 100644
--- a/manifest.uuid
+++ b/manifest.uuid
@@ -1 +1 @@
-b95644eafdd42293096a3760af8b2110f3c7d83feecdeff5ff9f008d9748e874
+0b7f4b97e68f17ae2fec86017cdb170f3b318a71cda34b5c82ec2d9df780564f
diff --git a/src/select.c b/src/select.c
index 9b910b890c..98f4047da0 100644
--- a/src/select.c
+++ b/src/select.c
@@ -2586,7 +2586,7 @@ static CollSeq *multiSelectCollSeq(Parse *pParse, Select *p, int iCol){
 */
 static KeyInfo *multiSelectByMergeKeyInfo(Parse *pParse, Select *p, int nExtra){
   ExprList *pOrderBy = p->pOrderBy;
-  int nOrderBy = ALWAYS(pOrderBy!=0) ? pOrderBy->nExpr : 0;
+  int nOrderBy = (pOrderBy!=0) ? pOrderBy->nExpr : 0;
   sqlite3 *db = pParse->db;
   KeyInfo *pRet = sqlite3KeyInfoAlloc(db, nOrderBy+nExtra, 1);
   if( pRet ){
@@ -3389,10 +3389,8 @@ static int generateOutputSubroutine(
 **    AeqB: ...
 **    AgtB: ...
 **    Init: initialize coroutine registers
-**          yield coA
-**          if eof(A) goto EofA
-**          yield coB
-**          if eof(B) goto EofB
+**          yield coA, on eof goto EofA
+**          yield coB, on eof goto EofB
 **    Cmpr: Compare A, B
 **          Jump AltB, AeqB, AgtB
 **     End: ...
@@ -3484,26 +3482,29 @@ static int multiSelectByMerge(
   }
 
   /* Compute the comparison permutation and keyinfo that is used with
-  ** the permutation used to determine if the next
-  ** row of results comes from selectA or selectB.  Also add explicit
-  ** collations to the ORDER BY clause terms so that when the subqueries
-  ** to the right and the left are evaluated, they use the correct
-  ** collation.
+  ** the permutation to determine if the next row of results comes
+  ** from selectA or selectB.  Also add literal collations to the
+  ** ORDER BY clause terms so that when selectA and selectB are
+  ** evaluated, they use the correct collation.
   */
   aPermute = sqlite3DbMallocRawNN(db, sizeof(u32)*(nOrderBy + 1));
   if( aPermute ){
     struct ExprList_item *pItem;
+    int bKeep = 0;
     aPermute[0] = nOrderBy;
     for(i=1, pItem=pOrderBy->a; i<=nOrderBy; i++, pItem++){
       assert( pItem!=0 );
       assert( pItem->u.x.iOrderByCol>0 );
       assert( pItem->u.x.iOrderByCol<=p->pEList->nExpr );
       aPermute[i] = pItem->u.x.iOrderByCol - 1;
+      if( aPermute[i]!=i-1 ) bKeep = 1;
+    }
+     if( bKeep==0 ){
+      sqlite3DbFreeNN(db, aPermute);
+      aPermute = 0;
     }
-    pKeyMerge = multiSelectByMergeKeyInfo(pParse, p, 1);
-  }else{
-    pKeyMerge = 0;
   }
+  pKeyMerge = multiSelectByMergeKeyInfo(pParse, p, 1);
 
   /* Allocate a range of temporary registers and the KeyInfo needed
   ** for the logic that removes duplicate result rows when the
@@ -3657,7 +3658,6 @@ static int multiSelectByMerge(
 
   /* Generate code to handle the case of A<B
   */
-  VdbeNoopComment((v, "SUBR: A-lt-B"));
   addrAltB = sqlite3VdbeAddOp2(v, OP_Gosub, regOutA, addrOutA);
   VdbeComment((v, "out-A"));
   sqlite3VdbeAddOp2(v, OP_Yield, regAddrA, addrEofA); VdbeCoverage(v);
@@ -3672,38 +3672,43 @@ static int multiSelectByMerge(
     addrAeqB = addrAltB;
     addrAltB++;
   }else{
-    VdbeNoopComment((v, "SUBR: A-eq-B"));
-    addrAeqB =
-    sqlite3VdbeAddOp2(v, OP_Yield, regAddrA, addrEofA); VdbeCoverage(v);
-    VdbeComment((v, "next-A"));
-    sqlite3VdbeGoto(v, labelCmpr);
+    addrAeqB = addrAltB + 1;
   }
 
   /* Generate code to handle the case of A>B
   */
-  VdbeNoopComment((v, "SUBR: A-gt-B"));
   addrAgtB = sqlite3VdbeCurrentAddr(v);
   if( op==TK_ALL || op==TK_UNION ){
     sqlite3VdbeAddOp2(v, OP_Gosub, regOutB, addrOutB);
     VdbeComment((v, "out-B"));
+    sqlite3VdbeAddOp2(v, OP_Yield, regAddrB, addrEofB); VdbeCoverage(v);
+    VdbeComment((v, "next-B"));
+    sqlite3VdbeGoto(v, labelCmpr);
+  }else{
+    addrAgtB++; /* Just do next-B.  Might as well use the next-B call
+                ** in the next code block */
   }
-  sqlite3VdbeAddOp2(v, OP_Yield, regAddrB, addrEofB); VdbeCoverage(v);
-  VdbeComment((v, "next-B"));
-  sqlite3VdbeGoto(v, labelCmpr);
 
   /* This code runs once to initialize everything.
   */
   sqlite3VdbeJumpHere(v, addr1);
   sqlite3VdbeAddOp2(v, OP_Yield, regAddrA, addrEofA_noB); VdbeCoverage(v);
+  VdbeComment((v, "next-A"));
+  /* v---  Also the A>B case for EXCEPT and INTERSECT */
   sqlite3VdbeAddOp2(v, OP_Yield, regAddrB, addrEofB); VdbeCoverage(v);
+  VdbeComment((v, "next-B"));
 
   /* Implement the main merge loop
   */
+  if( aPermute!=0 ){
+    sqlite3VdbeAddOp4(v, OP_Permutation, 0, 0, 0, (char*)aPermute, P4_INTARRAY);
+  }
   sqlite3VdbeResolveLabel(v, labelCmpr);
-  sqlite3VdbeAddOp4(v, OP_Permutation, 0, 0, 0, (char*)aPermute, P4_INTARRAY);
   sqlite3VdbeAddOp4(v, OP_Compare, destA.iSdst, destB.iSdst, nOrderBy,
                          (char*)pKeyMerge, P4_KEYINFO);
-  sqlite3VdbeChangeP5(v, OPFLAG_PERMUTE);
+  if( aPermute!=0 ){
+    sqlite3VdbeChangeP5(v, OPFLAG_PERMUTE);
+  }
   sqlite3VdbeAddOp3(v, OP_Jump, addrAltB, addrAeqB, addrAgtB);
   VdbeCoverageIf(v, op==TK_ALL);
   VdbeCoverageIf(v, op==TK_UNION);