From: drh <drh@noemail.net>
Date: Wed, 19 Jun 2013 12:34:13 +0000 (+0000)
Subject: Simplify and add invariants to the WhereLoop merging logic inside of
X-Git-Tag: version-3.8.0~134^2~7
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=dbb80234dabefcb518fb09fa073b6b09bd30f3af;p=thirdparty%2Fsqlite.git

Simplify and add invariants to the WhereLoop merging logic inside of
whereLoopInsert().

FossilOrigin-Name: 8f27f35f288434b9e7bc503c608f1e2b590ade4d
---

diff --git a/manifest b/manifest
index d232347684..37bf8cca81 100644
--- a/manifest
+++ b/manifest
@@ -1,5 +1,5 @@
-C Fix\scompiler\swarnings.\s\sFix\sa\sharmless\soff-by-one\serror\sin\sthe\ssolver.
-D 2013-06-19T03:27:12.614
+C Simplify\sand\sadd\sinvariants\sto\sthe\sWhereLoop\smerging\slogic\sinside\sof\nwhereLoopInsert().
+D 2013-06-19T12:34:13.186
 F Makefile.arm-wince-mingw32ce-gcc d6df77f1f48d690bd73162294bbba7f59507c72f
 F Makefile.in 5e41da95d92656a5004b03d3576e8b226858a28e
 F Makefile.linux-gcc 91d710bdc4998cb015f39edf3cb314ec4f4d7e23
@@ -289,7 +289,7 @@ F src/vtab.c b05e5f1f4902461ba9f5fc49bb7eb7c3a0741a83
 F src/wal.c 436bfceb141b9423c45119e68e444358ee0ed35d
 F src/wal.h df01efe09c5cb8c8e391ff1715cca294f89668a4
 F src/walker.c 4fa43583d0a84b48f93b1e88f11adf2065be4e73
-F src/where.c 5cc059bd283fe9f99800270c797fabdcbef8009a
+F src/where.c e5ecc3d12c5b9d66d13f786e80641614530d1957
 F test/8_3_names.test ebbb5cd36741350040fd28b432ceadf495be25b2
 F test/aggerror.test a867e273ef9e3d7919f03ef4f0e8c0d2767944f2
 F test/aggnested.test 45c0201e28045ad38a530b5a144b73cd4aa2cfd6
@@ -1096,7 +1096,7 @@ F tool/warnings-clang.sh f6aa929dc20ef1f856af04a730772f59283631d4
 F tool/warnings.sh fbc018d67fd7395f440c28f33ef0f94420226381
 F tool/wherecosttest.c f407dc4c79786982a475261866a161cd007947ae
 F tool/win/sqlite.vsix 97894c2790eda7b5bce3cc79cb2a8ec2fde9b3ac
-P 4fbb0c4d26c54aaefbe5397cde2a0b9d2ce3885f
-R dae7f42197a8d862e7c14dd3769614f8
+P 10021941d0258951b916e788881df140113f0597
+R 38e2e388820d13ceac39bea07ba5a7cc
 U drh
-Z e26ab5beb4ba36d99e52a8a301bdec10
+Z 087e132035ea5a36d1e5d81e4344a21a
diff --git a/manifest.uuid b/manifest.uuid
index 011a8dd71f..8aac6362f2 100644
--- a/manifest.uuid
+++ b/manifest.uuid
@@ -1 +1 @@
-10021941d0258951b916e788881df140113f0597
\ No newline at end of file
+8f27f35f288434b9e7bc503c608f1e2b590ade4d
\ No newline at end of file
diff --git a/src/where.c b/src/where.c
index 73fdcaa431..2626306c24 100644
--- a/src/where.c
+++ b/src/where.c
@@ -4115,14 +4115,30 @@ static int whereLoopInsert(WhereLoopBuilder *pBuilder, WhereLoop *pTemplate){
   ** priority over pTemplate.
   */
   for(ppPrev=&pWInfo->pLoops, p=*ppPrev; p; ppPrev=&p->pNextLoop, p=*ppPrev){
-    if( p->iTab!=pTemplate->iTab || p->iSortIdx!=pTemplate->iSortIdx ) continue;
+    if( p->iTab!=pTemplate->iTab || p->iSortIdx!=pTemplate->iSortIdx ){
+      /* If either the iTab or iSortIdx values for two WhereLoop are different
+      ** then those WhereLoops need to be considered separately.  Neither is
+      ** a candidate to replace the other. */
+      continue;
+    }
+    /* In the current implementation, the rSetup value is either zero
+    ** or the cost of building an automatic index (NlogN) and the NlogN
+    ** is the same for compatible WhereLoops. */
+    assert( p->rSetup==0 || pTemplate->rSetup==0 
+                 || p->rSetup==pTemplate->rSetup );
+
+    /* whereLoopAddBtree() always generates and inserts the automatic index
+    ** case first.  Hence compatible candidate WhereLoops never have a larger
+    ** rSetup. Call this SETUP-INVARIANT */
+    assert( p->rSetup>=pTemplate->rSetup );
+
     if( (p->prereq & pTemplate->prereq)==p->prereq
      && p->rSetup<=pTemplate->rSetup
      && p->rRun<=pTemplate->rRun
     ){
       /* This branch taken when p is equal or better than pTemplate in 
       ** all of (1) dependences (2) setup-cost, and (3) run-cost. */
-      testcase( p->rRun==pTemplate->rRun );
+      assert( p->rSetup==pTemplate->rSetup );
       if( p->nLTerm<pTemplate->nLTerm
        && (p->wsFlags & WHERE_INDEXED)!=0
        && (pTemplate->wsFlags & WHERE_INDEXED)!=0
@@ -4133,38 +4149,22 @@ static int whereLoopInsert(WhereLoopBuilder *pBuilder, WhereLoop *pTemplate){
         ** more terms of the index */
         pNext = p->pNextLoop;
         break;
-      }else if( p->nOut>pTemplate->nOut
-       && p->rSetup==pTemplate->rSetup
-       && p->rRun==pTemplate->rRun
-      ){
-        /* Overwrite an existing WhereLoop with the same cost but more
-        ** outputs */
-        pNext = p->pNextLoop;
-        break;
       }else{
         /* pTemplate is not helpful.
         ** Return without changing or adding anything */
         goto whereLoopInsert_noop;
       }
     }
-    testcase( (p->prereq & pTemplate->prereq)==p->prereq
-              && p->rSetup<=pTemplate->rSetup
-              && p->rRun==pTemplate->rRun+1 );
     if( (p->prereq & pTemplate->prereq)==pTemplate->prereq
-     && p->rSetup>=pTemplate->rSetup
      && p->rRun>=pTemplate->rRun
+     && ALWAYS(p->rSetup>=pTemplate->rSetup) /* See SETUP-INVARIANT above */
     ){
       /* Overwrite an existing WhereLoop with a better one: one that is
       ** better at one of (1) dependences, (2) setup-cost, or (3) run-cost
       ** and is no worse in any of those categories. */
-      testcase( p->rSetup==pTemplate->rSetup );
-      testcase( p->rRun==pTemplate->rRun );
       pNext = p->pNextLoop;
       break;
     }
-    testcase( (p->prereq & pTemplate->prereq)==pTemplate->prereq
-              && p->rSetup>=pTemplate->rSetup
-              && p->rRun==pTemplate->rRun-1 );
   }
 
   /* If we reach this point it means that either p[] should be overwritten