Improvements to IN operator code generator comments. Avoid unnecessary

Copy operations on the LHS of the IN operator.

FossilOrigin-Name: b6344298783a1207cba3f635939ddc9ba922ab67

manifest

@@ -1,5 +1,5 @@
-C Corrections\sto\sthe\sIN-operator\snotes.
+C Improvements\sto\sIN\soperator\scode\sgenerator\scomments.\s\sAvoid\sunnecessary\nCopy\soperations\son\sthe\sLHS\sof\sthe\sIN\soperator.
-D 2016-08-25T14:23:59.673
+D 2016-08-25T15:46:25.026
 F Makefile.in cfd8fb987cd7a6af046daa87daa146d5aad0e088
 F Makefile.linux-gcc 7bc79876b875010e8c8f9502eb935ca92aa3c434
 F Makefile.msc d66d0395c38571aab3804f8db0fa20707ae4609a
@@ -338,7 +338,7 @@ F src/ctime.c e77f3dc297b4b65c96da78b4ae4272fdfae863d7
 F src/date.c 95c9a8d00767e7221a8e9a31f4e913fc8029bf6b
 F src/dbstat.c 19ee7a4e89979d4df8e44cfac7a8f905ec89b77d
 F src/delete.c 76c084f0265f4a3cd1ecf17eee112a94f1ccbc05
-F src/expr.c 866bcb6e85806beb0f96e651e9d17811e1ecbda5
+F src/expr.c 1c003fcb9c5a6f8c54f6392378225d578be2a086
 F src/fault.c 160a0c015b6c2629d3899ed2daf63d75754a32bb
 F src/fkey.c e2be0968c1adc679c87e467aa5b4f167588f38a8
 F src/func.c 29cc9acb170ec1387b9f63eb52cd85f8de96c771
@@ -1521,7 +1521,7 @@ F vsixtest/vsixtest.tcl 6a9a6ab600c25a91a7acc6293828957a386a8a93
 F vsixtest/vsixtest.vcxproj.data 2ed517e100c66dc455b492e1a33350c1b20fbcdc
 F vsixtest/vsixtest.vcxproj.filters 37e51ffedcdb064aad6ff33b6148725226cd608e
 F vsixtest/vsixtest_TemporaryKey.pfx e5b1b036facdb453873e7084e1cae9102ccc67a0
-P d256b2caeb9e3eb5dd88bb569ec71f91e9991c81
+P 25033ee94538289ba7e0147da30a18300047123f
-R e83420368d9fa99d84d7c5701ecba45b
+R e1cedb5c8edd4d27c5fcda8527491fbe
 U drh
-Z a8948efc181e8ffaf5af6c9f4ff55b46
+Z c3029179ef3a13ce81541f0730bc01a8

manifest.uuid

@@ -1 +1 @@
-25033ee94538289ba7e0147da30a18300047123f
+b6344298783a1207cba3f635939ddc9ba922ab67

src/expr.c

@@ -2637,16 +2637,19 @@ int sqlite3ExprCheckIN(Parse *pParse, Expr *pIn){
 **      x IN (SELECT ...)
 **      x IN (value, value, ...)
 **
-** The left-hand side (LHS) is a scalar expression.  The right-hand side (RHS)
+** The left-hand side (LHS) is a scalar or vector expression.  The 
-** is an array of zero or more values.  The expression is true if the LHS is
+** right-hand side (RHS) is an array of zero or more values.  The IN operator
-** contained within the RHS.  The value of the expression is unknown (NULL)
+** is true if the LHS is contained within the RHS.  The result is false
-** if the LHS is NULL or if the LHS is not contained within the RHS and the
+** if the LHS is definitely not in the RHS.  The result is NULL if the presence
-** RHS contains one or more NULL values.
+** of the LHS in the RHS cannot be determined due to NULLs.
 **
 ** This routine generates code that jumps to destIfFalse if the LHS is not 
 ** contained within the RHS.  If due to NULLs we cannot determine if the LHS
 ** is contained in the RHS then jump to destIfNull.  If the LHS is contained
 ** within the RHS then fall through.
+**
+** See the separate in-operator.md documentation file in the canonical
+** SQLite source tree for additional information.
 */
 static void sqlite3ExprCodeIN(
   Parse *pParse,        /* Parsing and code generating context */
@@ -2660,22 +2663,18 @@ static void sqlite3ExprCodeIN(
   Vdbe *v;              /* Statement under construction */
   int *aiMap = 0;       /* Map from vector field to index column */
   char *zAff = 0;       /* Affinity string for comparisons */
-  int nVector;          /* Size of vectors for this IN(...) op */
+  int nVector;                 /* Size of vectors for this IN operator */
   int iDummy;                  /* Dummy parameter to exprCodeVector() */
-  Expr *pLeft = pExpr->pLeft;
+  Expr *pLeft = pExpr->pLeft;  /* The LHS of the IN operator */
-  int i;
+  int i;                       /* loop counter */
 
   if( sqlite3ExprCheckIN(pParse, pExpr) ) return;
   zAff = exprINAffinity(pParse, pExpr);
-  if( zAff==0 ) return;
   nVector = sqlite3ExprVectorSize(pExpr->pLeft);
   aiMap = (int*)sqlite3DbMallocZero(
       pParse->db, nVector*(sizeof(int) + sizeof(char)) + 1
   );
-  if( aiMap==0 ){
+  if( pParse->db->mallocFailed ) goto end_code_IN_op;
-    sqlite3DbFree(pParse->db, zAff);
-    return;
-  }
 
   /* Attempt to compute the RHS. After this step, if anything other than
   ** IN_INDEX_NOOP is returned, the table opened ith cursor pExpr->iTable 
@@ -2691,17 +2690,33 @@ static void sqlite3ExprCodeIN(
   assert( pParse->nErr || nVector==1 || eType==IN_INDEX_EPH
        || eType==IN_INDEX_INDEX_ASC || eType==IN_INDEX_INDEX_DESC 
   );
+#ifdef SQLITE_DEBUG
+  /* Confirm that aiMap[] contains nVector integer values between 0 and
+  ** nVector-1. */
+  for(i=0; i<nVector; i++){
+    int j, cnt;
+    for(cnt=j=0; j<nVector; j++) if( aiMap[j]==i ) cnt++;
+    assert( cnt==1 );
+  }
+#endif
 
   /* Code the LHS, the <expr> from "<expr> IN (...)". If the LHS is a 
   ** vector, then it is stored in an array of nVector registers starting 
   ** at r1.
   */
-  r1 = sqlite3GetTempRange(pParse, nVector);
   sqlite3ExprCachePush(pParse);
   r2 = exprCodeVector(pParse, pLeft, &iDummy);
+  for(i=0; i<nVector && aiMap[i]==i; i++){}
+  if( i==nVector ){
+    /* LHS fields are already in the correct order */
+    r1 = r2;
+  }else{
+    /* Need to reorder the LHS fields according to aiMap */
+    r1 = sqlite3GetTempRange(pParse, nVector);
     for(i=0; i<nVector; i++){
       sqlite3VdbeAddOp3(v, OP_Copy, r2+i, r1+aiMap[i], 0);
     }
+  }
 
   /* If sqlite3FindInIndex() did not find or create an index that is
   ** suitable for evaluating the IN operator, then evaluate using a
@@ -2861,11 +2876,12 @@ static void sqlite3ExprCodeIN(
       }
     }
   }
-  sqlite3ReleaseTempReg(pParse, r1);
+  if( r2!=r1 ) sqlite3ReleaseTempReg(pParse, r1);
   sqlite3ExprCachePop(pParse);
+  VdbeComment((v, "end IN expr"));
+end_code_IN_op:
   sqlite3DbFree(pParse->db, aiMap);
   sqlite3DbFree(pParse->db, zAff);
-  VdbeComment((v, "end IN expr"));
 }
 #endif /* SQLITE_OMIT_SUBQUERY */