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Overview
Comment:Improvements to IN operator code generator comments. Avoid unnecessary Copy operations on the LHS of the IN operator.
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SHA1: b6344298783a1207cba3f635939ddc9ba922ab67
User & Date: drh 2016-08-25 15:46:25
Context
2016-08-25
17:40
Further refinement of the in-operator.md documentation. check-in: df064837 user: drh tags: rowvalue
15:46
Improvements to IN operator code generator comments. Avoid unnecessary Copy operations on the LHS of the IN operator. check-in: b6344298 user: drh tags: rowvalue
14:23
Corrections to the IN-operator notes. check-in: 25033ee9 user: drh tags: rowvalue
Changes
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Changes to src/expr.c.

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#ifndef SQLITE_OMIT_SUBQUERY
/*
** Generate code for an IN expression.
**
**      x IN (SELECT ...)
**      x IN (value, value, ...)
**
** The left-hand side (LHS) is a scalar expression.  The right-hand side (RHS)
** is an array of zero or more values.  The expression is true if the LHS is
** contained within the RHS.  The value of the expression is unknown (NULL)
** if the LHS is NULL or if the LHS is not contained within the RHS and the
** RHS contains one or more NULL values.
**
** 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.



*/
static void sqlite3ExprCodeIN(
  Parse *pParse,        /* Parsing and code generating context */
  Expr *pExpr,          /* The IN expression */
  int destIfFalse,      /* Jump here if LHS is not contained in the RHS */
  int destIfNull        /* Jump here if the results are unknown due to NULLs */
){
  int rRhsHasNull = 0;  /* Register that is true if RHS contains NULL values */
  int eType;            /* Type of the RHS */
  int r1, r2;           /* Temporary use registers */
  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 iDummy;           /* Dummy parameter to exprCodeVector() */
  Expr *pLeft = pExpr->pLeft;
  int i;

  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 ){
    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 
  ** contains the values that make up the RHS. If IN_INDEX_NOOP is returned,
  ** the RHS has not yet been coded.  */
  v = pParse->pVdbe;
  assert( v!=0 );       /* OOM detected prior to this routine */
................................................................................
  eType = sqlite3FindInIndex(pParse, pExpr,
                             IN_INDEX_MEMBERSHIP | IN_INDEX_NOOP_OK,
                             destIfFalse==destIfNull ? 0 : &rRhsHasNull, aiMap);

  assert( pParse->nErr || nVector==1 || eType==IN_INDEX_EPH
       || eType==IN_INDEX_INDEX_ASC || eType==IN_INDEX_INDEX_DESC 
  );










  /* 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; 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
  ** sequence of comparisons.
  */
  if( eType==IN_INDEX_NOOP ){
................................................................................
        sqlite3VdbeAddOp2(v, OP_IsNull, rRhsHasNull, destIfNull);
        VdbeCoverage(v);
        sqlite3VdbeGoto(v, destIfFalse);
        sqlite3VdbeJumpHere(v, addr1);
      }
    }
  }
  sqlite3ReleaseTempReg(pParse, r1);
  sqlite3ExprCachePop(pParse);


  sqlite3DbFree(pParse->db, aiMap);
  sqlite3DbFree(pParse->db, zAff);
  VdbeComment((v, "end IN expr"));
}
#endif /* SQLITE_OMIT_SUBQUERY */

#ifndef SQLITE_OMIT_FLOATING_POINT
/*
** Generate an instruction that will put the floating point
** value described by z[0..n-1] into register iMem.







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#ifndef SQLITE_OMIT_SUBQUERY
/*
** Generate code for an IN expression.
**
**      x IN (SELECT ...)
**      x IN (value, value, ...)
**
** The left-hand side (LHS) is a scalar or vector expression.  The 
** right-hand side (RHS) is an array of zero or more values.  The IN operator
** is true if the LHS is contained within the RHS.  The result is false
** if the LHS is definitely not in the RHS.  The result is NULL if the presence
** 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 */
  Expr *pExpr,          /* The IN expression */
  int destIfFalse,      /* Jump here if LHS is not contained in the RHS */
  int destIfNull        /* Jump here if the results are unknown due to NULLs */
){
  int rRhsHasNull = 0;  /* Register that is true if RHS contains NULL values */
  int eType;            /* Type of the RHS */
  int r1, r2;           /* Temporary use registers */
  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 operator */
  int iDummy;                  /* Dummy parameter to exprCodeVector() */
  Expr *pLeft = pExpr->pLeft;  /* The LHS of the IN operator */
  int i;                       /* loop counter */

  if( sqlite3ExprCheckIN(pParse, pExpr) ) return;
  zAff = exprINAffinity(pParse, pExpr);

  nVector = sqlite3ExprVectorSize(pExpr->pLeft);
  aiMap = (int*)sqlite3DbMallocZero(
      pParse->db, nVector*(sizeof(int) + sizeof(char)) + 1
  );
  if( pParse->db->mallocFailed ) goto end_code_IN_op;




  /* Attempt to compute the RHS. After this step, if anything other than
  ** IN_INDEX_NOOP is returned, the table opened ith cursor pExpr->iTable 
  ** contains the values that make up the RHS. If IN_INDEX_NOOP is returned,
  ** the RHS has not yet been coded.  */
  v = pParse->pVdbe;
  assert( v!=0 );       /* OOM detected prior to this routine */
................................................................................
  eType = sqlite3FindInIndex(pParse, pExpr,
                             IN_INDEX_MEMBERSHIP | IN_INDEX_NOOP_OK,
                             destIfFalse==destIfNull ? 0 : &rRhsHasNull, aiMap);

  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.
  */

  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
  ** sequence of comparisons.
  */
  if( eType==IN_INDEX_NOOP ){
................................................................................
        sqlite3VdbeAddOp2(v, OP_IsNull, rRhsHasNull, destIfNull);
        VdbeCoverage(v);
        sqlite3VdbeGoto(v, destIfFalse);
        sqlite3VdbeJumpHere(v, addr1);
      }
    }
  }
  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);

}
#endif /* SQLITE_OMIT_SUBQUERY */

#ifndef SQLITE_OMIT_FLOATING_POINT
/*
** Generate an instruction that will put the floating point
** value described by z[0..n-1] into register iMem.