From c0359f0490fd80f7106d939ffea16e3fabdbd708 Mon Sep 17 00:00:00 2001
From: drh <>
Date: Fri, 28 May 2021 14:28:54 +0000
Subject: [PATCH] If a subquery is used to drive an index, this change avoids
 making an extra copy of the result of that subquery.  But, such situations
 are probably sufficiently unusual that the added complexity of this
 enhancement is not worth the performance gain.  So I'm going to park this
 check-in on a branch. If we later find a use case to justify it, we can merge
 it to trunk then. This is the "further change" that was promised by the prior
 check-in comment.

FossilOrigin-Name: 4488cb883e155a7466946d25569ab2816c4a8de9d4c7d540f5053ea5334e7ae5
---
 manifest        | 15 +++++++++------
 manifest.uuid   |  2 +-
 src/wherecode.c |  7 ++++++-
 3 files changed, 16 insertions(+), 8 deletions(-)

diff --git a/manifest b/manifest
index cc15943c16..37759ca1d8 100644
--- a/manifest
+++ b/manifest
@@ -1,5 +1,5 @@
-C Make\sa\sdeep\scopy\sof\sthe\sresult\sof\sa\ssubquery\sin\scase\sthe\ssubquery\sis\nreused.\s\sFix\sfor\sthe\sproblem\sreported\sby\n[forum:/forumpost/28216b36ac|forum\spost\s28216b36ac]\sand\sintroduced\sby\ncheck-in\s[f30fb19ff763a7cb].\s\sFurther\schanges\sto\stry\sto\soptimize\sthe\snew\nOP_Copy\sopcode\sback\sinto\seither\sOP_SCopy\sor\sOP_Move\swill\sbe\sattempted\nseparately.\s\sA\stest\scase\swill\sbe\sin\sTH3.
-D 2021-05-28T12:48:31.685
+C If\sa\ssubquery\sis\sused\sto\sdrive\san\sindex,\sthis\schange\savoids\smaking\san\sextra\ncopy\sof\sthe\sresult\sof\sthat\ssubquery.\s\sBut,\ssuch\ssituations\sare\sprobably\nsufficiently\sunusual\sthat\sthe\sadded\scomplexity\sof\sthis\senhancement\sis\snot\nworth\sthe\sperformance\sgain.\s\sSo\sI'm\sgoing\sto\spark\sthis\scheck-in\son\sa\sbranch.\nIf\swe\slater\sfind\sa\suse\scase\sto\sjustify\sit,\swe\scan\smerge\sit\sto\strunk\sthen.\nThis\sis\sthe\s"further\schange"\sthat\swas\spromised\sby\sthe\sprior\scheck-in\scomment.
+D 2021-05-28T14:28:54.261
 F .fossil-settings/empty-dirs dbb81e8fc0401ac46a1491ab34a7f2c7c0452f2f06b54ebb845d024ca8283ef1
 F .fossil-settings/ignore-glob 35175cdfcf539b2318cb04a9901442804be81cd677d8b889fcc9149c21f239ea
 F LICENSE.md df5091916dbb40e6e9686186587125e1b2ff51f022cc334e886c19a0e9982724
@@ -633,7 +633,7 @@ F src/wal.h c3aa7825bfa2fe0d85bef2db94655f99870a285778baa36307c0a16da32b226a
 F src/walker.c 7342becedf3f8a26f9817f08436bdf8b56ad69af83705f6b9320a0ad3092c2ac
 F src/where.c 32f41c3c93c6785e0077e3a2cdc669c3ccfe70173787847be77f294c18fc7dc3
 F src/whereInt.h 9248161dd004f625ce5d3841ca9b99fed3fc8d61522cf76340fc5217dbe1375b
-F src/wherecode.c 9f1f65d11437b25cd0a1497a170514c785f19ce6ad9d3e6fc73719cb5a49012f
+F src/wherecode.c bcfee3789a7d3da1f3f8a76c1b20c95d6c0fc4ea93c5d9b03206a432ac8b1cc4
 F src/whereexpr.c 5a9c9f5d2dac4bcdcaae3035034b4667523f731df228e0bb1d4efc669efa9da5
 F src/window.c a6d624d83b2d5b3cfb82bb437a2fbae759c928d47dc9ad1338a9419269181bb2
 F test/8_3_names.test ebbb5cd36741350040fd28b432ceadf495be25b2
@@ -1918,7 +1918,10 @@ F vsixtest/vsixtest.tcl 6a9a6ab600c25a91a7acc6293828957a386a8a93
 F vsixtest/vsixtest.vcxproj.data 2ed517e100c66dc455b492e1a33350c1b20fbcdc
 F vsixtest/vsixtest.vcxproj.filters 37e51ffedcdb064aad6ff33b6148725226cd608e
 F vsixtest/vsixtest_TemporaryKey.pfx e5b1b036facdb453873e7084e1cae9102ccc67a0
-P 21676731cedae27d1ab9fe62b269001ae6e3eeb3caa87b4f5536f777631a8bbc
-R 77e951a6e7b5327d1f646c5968da6983
+P c9f0b9cb0aef107265435e22c164dd3c974eadfd00abf7cfd4fc7ec95c0dd7d0
+R c044497982752ba303617f7de106b59c
+T *branch * copy-optimization
+T *sym-copy-optimization *
+T -sym-trunk *
 U drh
-Z 20c9ad1ef6610380252081cdda3138d3
+Z 0c06d6f1ffda88b03d3d1e66ad233058
diff --git a/manifest.uuid b/manifest.uuid
index f8745ea2ba..121f771c64 100644
--- a/manifest.uuid
+++ b/manifest.uuid
@@ -1 +1 @@
-c9f0b9cb0aef107265435e22c164dd3c974eadfd00abf7cfd4fc7ec95c0dd7d0
\ No newline at end of file
+4488cb883e155a7466946d25569ab2816c4a8de9d4c7d540f5053ea5334e7ae5
\ No newline at end of file
diff --git a/src/wherecode.c b/src/wherecode.c
index 84fa1a1410..18f79e33e1 100644
--- a/src/wherecode.c
+++ b/src/wherecode.c
@@ -752,11 +752,16 @@ static int codeAllEqualityTerms(
     testcase( pTerm->wtFlags & TERM_VIRTUAL );
     r1 = codeEqualityTerm(pParse, pTerm, pLevel, j, bRev, regBase+j);
     if( r1!=regBase+j ){
+      assert( pTerm->pExpr->op==TK_EQ || pTerm->pExpr->op==TK_IS );
       if( nReg==1 ){
         sqlite3ReleaseTempReg(pParse, regBase);
         regBase = r1;
       }else{
-        sqlite3VdbeAddOp2(v, OP_Copy, r1, regBase+j);
+        if( ExprHasProperty(pTerm->pExpr->pRight, EP_VarSelect) ){
+          sqlite3VdbeAddOp3(v, OP_Move, r1, regBase+j, 1);
+        }else{
+          sqlite3VdbeAddOp2(v, OP_SCopy, r1, regBase+j);
+        }
       }
     }
     if( pTerm->eOperator & WO_IN ){
-- 
2.39.5