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Overview
Comment:Here is the beginnings of an effort to factor out the implementation of scalar subqueries to be implemented as subroutines at the end of the main body of bytecode, after the jump back to the OP_Init opcode. This is an incremental check-in that contains only preliminary changes.
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SHA3-256:50e5f390fbab4189c9700a2c62c951ab9acbf0a03c491e88f3e3bcf19a2311cc
User & Date: drh 2018-12-26 15:04:43
Context
2018-12-28
21:40
Merge performance enhancements and other patches. Leaf check-in: 44e1b55a user: drh tags: factor-out-scalar-subselect
2018-12-26
15:04
Here is the beginnings of an effort to factor out the implementation of scalar subqueries to be implemented as subroutines at the end of the main body of bytecode, after the jump back to the OP_Init opcode. This is an incremental check-in that contains only preliminary changes. check-in: 50e5f390 user: drh tags: factor-out-scalar-subselect
2018-12-25
00:15
Increase the number of parameters to sqlite3WhereCodeOneLoopStart() to encourage the compiler to inline that routine within sqlite3WhereBegin(). This gives a performance improvement. check-in: 3c2ad0e9 user: drh tags: reuse-subqueries
Changes
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Changes to src/build.c.

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    /* The cookie mask contains one bit for each database file open.
    ** (Bit 0 is for main, bit 1 is for temp, and so forth.)  Bits are
    ** set for each database that is used.  Generate code to start a
    ** transaction on each used database and to verify the schema cookie
    ** on each used database.
    */
    if( db->mallocFailed==0 
     && (DbMaskNonZero(pParse->cookieMask) || pParse->pConstExpr)
    ){
      int iDb, i;
      assert( sqlite3VdbeGetOp(v, 0)->opcode==OP_Init );
      sqlite3VdbeJumpHere(v, 0);
      for(iDb=0; iDb<db->nDb; iDb++){
        Schema *pSchema;
        if( DbMaskTest(pParse->cookieMask, iDb)==0 ) continue;
................................................................................
      */
      codeTableLocks(pParse);

      /* Initialize any AUTOINCREMENT data structures required.
      */
      sqlite3AutoincrementBegin(pParse);

      /* Code constant expressions that where factored out of inner loops */
      if( pParse->pConstExpr ){
        ExprList *pEL = pParse->pConstExpr;

        pParse->okConstFactor = 0;
        for(i=0; i<pEL->nExpr; i++){


          sqlite3ExprCode(pParse, pEL->a[i].pExpr, pEL->a[i].u.iConstExprReg);
        }





      }


      /* Finally, jump back to the beginning of the executable code. */
      sqlite3VdbeGoto(v, 1);

    }
  }


  /* Get the VDBE program ready for execution
  */
  if( v && pParse->nErr==0 && !db->mallocFailed ){







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    /* The cookie mask contains one bit for each database file open.
    ** (Bit 0 is for main, bit 1 is for temp, and so forth.)  Bits are
    ** set for each database that is used.  Generate code to start a
    ** transaction on each used database and to verify the schema cookie
    ** on each used database.
    */
    if( db->mallocFailed==0 
     && (DbMaskNonZero(pParse->cookieMask) || pParse->pAuxExpr)
    ){
      int iDb, i;
      assert( sqlite3VdbeGetOp(v, 0)->opcode==OP_Init );
      sqlite3VdbeJumpHere(v, 0);
      for(iDb=0; iDb<db->nDb; iDb++){
        Schema *pSchema;
        if( DbMaskTest(pParse->cookieMask, iDb)==0 ) continue;
................................................................................
      */
      codeTableLocks(pParse);

      /* Initialize any AUTOINCREMENT data structures required.
      */
      sqlite3AutoincrementBegin(pParse);


      if( pParse->pAuxExpr ){
        ExprList *pEL = pParse->pAuxExpr;
        struct ExprList_item *pX;
        pParse->okConstFactor = 0;
        /* Code constant expressions that where factored out of inner loops */
        for(pX=pEL->a, i=pEL->nExpr; i>0; i--, pX++){
          if( pX->bAuxSubrtn ) continue;
          sqlite3ExprCode(pParse, pX->pExpr, pX->u.iConstExprReg);
        }
        sqlite3VdbeGoto(v, 1);  /* Jump back to the main code */
        /* Code subroutines factored out from main */
        for(pX=pEL->a, i=pEL->nExpr; i>0; i--, pX++){
          if( !pX->bAuxSubrtn ) continue;
          /* sqlite3ExprCode(pParse, pX->pExpr, pX->u.iConstExprReg); */
        }

      }else{
        /* Jump back to the beginning of main */
        sqlite3VdbeGoto(v, 1);
      }
    }
  }


  /* Get the VDBE program ready for execution
  */
  if( v && pParse->nErr==0 && !db->mallocFailed ){

Changes to src/expr.c.

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**   (1) the expression is constant, and
**   (2) the expression does originate in the ON or USING clause
**       of a LEFT JOIN, and
**   (3) the expression does not contain any EP_FixedCol TK_COLUMN
**       operands created by the constant propagation optimization.
**
** When this routine returns true, it indicates that the expression
** can be added to the pParse->pConstExpr list and evaluated once when
** the prepared statement starts up.  See sqlite3ExprCodeAtInit().
*/
int sqlite3ExprIsConstantNotJoin(Expr *p){
  return exprIsConst(p, 2, 0);
}

/*
................................................................................
int sqlite3ExprCodeAtInit(
  Parse *pParse,    /* Parsing context */
  Expr *pExpr,      /* The expression to code when the VDBE initializes */
  int regDest       /* Store the value in this register */
){
  ExprList *p;
  assert( ConstFactorOk(pParse) );
  p = pParse->pConstExpr;
  if( regDest<0 && p ){
    struct ExprList_item *pItem;
    int i;
    for(pItem=p->a, i=p->nExpr; i>0; pItem++, i--){
      if( pItem->reusable && sqlite3ExprCompare(0,pItem->pExpr,pExpr,-1)==0 ){
        return pItem->u.iConstExprReg;
      }
................................................................................
  p = sqlite3ExprListAppend(pParse, p, pExpr);
  if( p ){
     struct ExprList_item *pItem = &p->a[p->nExpr-1];
     pItem->reusable = regDest<0;
     if( regDest<0 ) regDest = ++pParse->nMem;
     pItem->u.iConstExprReg = regDest;
  }
  pParse->pConstExpr = p;
  return regDest;
}

/*
** Generate code to evaluate an expression and store the results
** into a register.  Return the register number where the results
** are stored.
................................................................................
  compRight.pRight = pExpr->x.pList->a[1].pExpr;
  exprToRegister(&exprX, exprCodeVector(pParse, &exprX, &regFree1));
  if( xJump ){
    xJump(pParse, &exprAnd, dest, jumpIfNull);
  }else{
    /* Mark the expression is being from the ON or USING clause of a join
    ** so that the sqlite3ExprCodeTarget() routine will not attempt to move
    ** it into the Parse.pConstExpr list.  We should use a new bit for this,
    ** for clarity, but we are out of bits in the Expr.flags field so we
    ** have to reuse the EP_FromJoin bit.  Bummer. */
    exprX.flags |= EP_FromJoin;
    sqlite3ExprCodeTarget(pParse, &exprAnd, dest);
  }
  sqlite3ReleaseTempReg(pParse, regFree1);








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**   (1) the expression is constant, and
**   (2) the expression does originate in the ON or USING clause
**       of a LEFT JOIN, and
**   (3) the expression does not contain any EP_FixedCol TK_COLUMN
**       operands created by the constant propagation optimization.
**
** When this routine returns true, it indicates that the expression
** can be added to the pParse->pAuxExpr list and evaluated once when
** the prepared statement starts up.  See sqlite3ExprCodeAtInit().
*/
int sqlite3ExprIsConstantNotJoin(Expr *p){
  return exprIsConst(p, 2, 0);
}

/*
................................................................................
int sqlite3ExprCodeAtInit(
  Parse *pParse,    /* Parsing context */
  Expr *pExpr,      /* The expression to code when the VDBE initializes */
  int regDest       /* Store the value in this register */
){
  ExprList *p;
  assert( ConstFactorOk(pParse) );
  p = pParse->pAuxExpr;
  if( regDest<0 && p ){
    struct ExprList_item *pItem;
    int i;
    for(pItem=p->a, i=p->nExpr; i>0; pItem++, i--){
      if( pItem->reusable && sqlite3ExprCompare(0,pItem->pExpr,pExpr,-1)==0 ){
        return pItem->u.iConstExprReg;
      }
................................................................................
  p = sqlite3ExprListAppend(pParse, p, pExpr);
  if( p ){
     struct ExprList_item *pItem = &p->a[p->nExpr-1];
     pItem->reusable = regDest<0;
     if( regDest<0 ) regDest = ++pParse->nMem;
     pItem->u.iConstExprReg = regDest;
  }
  pParse->pAuxExpr = p;
  return regDest;
}

/*
** Generate code to evaluate an expression and store the results
** into a register.  Return the register number where the results
** are stored.
................................................................................
  compRight.pRight = pExpr->x.pList->a[1].pExpr;
  exprToRegister(&exprX, exprCodeVector(pParse, &exprX, &regFree1));
  if( xJump ){
    xJump(pParse, &exprAnd, dest, jumpIfNull);
  }else{
    /* Mark the expression is being from the ON or USING clause of a join
    ** so that the sqlite3ExprCodeTarget() routine will not attempt to move
    ** it into the Parse.pAuxExpr list.  We should use a new bit for this,
    ** for clarity, but we are out of bits in the Expr.flags field so we
    ** have to reuse the EP_FromJoin bit.  Bummer. */
    exprX.flags |= EP_FromJoin;
    sqlite3ExprCodeTarget(pParse, &exprAnd, dest);
  }
  sqlite3ReleaseTempReg(pParse, regFree1);

Changes to src/prepare.c.

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/*
** Free all memory allocations in the pParse object
*/
void sqlite3ParserReset(Parse *pParse){
  sqlite3 *db = pParse->db;
  sqlite3DbFree(db, pParse->aLabel);
  sqlite3ExprListDelete(db, pParse->pConstExpr);
  if( db ){
    assert( db->lookaside.bDisable >= pParse->disableLookaside );
    db->lookaside.bDisable -= pParse->disableLookaside;
  }
  pParse->disableLookaside = 0;
}








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/*
** Free all memory allocations in the pParse object
*/
void sqlite3ParserReset(Parse *pParse){
  sqlite3 *db = pParse->db;
  sqlite3DbFree(db, pParse->aLabel);
  sqlite3ExprListDelete(db, pParse->pAuxExpr);
  if( db ){
    assert( db->lookaside.bDisable >= pParse->disableLookaside );
    db->lookaside.bDisable -= pParse->disableLookaside;
  }
  pParse->disableLookaside = 0;
}

Changes to src/sqliteInt.h.

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  struct ExprList_item { /* For each expression in the list */
    Expr *pExpr;            /* The parse tree for this expression */
    char *zName;            /* Token associated with this expression */
    char *zSpan;            /* Original text of the expression */
    u8 sortOrder;           /* 1 for DESC or 0 for ASC */
    unsigned done :1;       /* A flag to indicate when processing is finished */
    unsigned bSpanIsTab :1; /* zSpan holds DB.TABLE.COLUMN */
    unsigned reusable :1;   /* Constant expression is reusable */
    unsigned bSorterRef :1; /* Defer evaluation until after sorting */

    union {
      struct {
        u16 iOrderByCol;      /* For ORDER BY, column number in result set */
        u16 iAlias;           /* Index into Parse.aAlias[] for zName */
      } x;
      int iConstExprReg;      /* Register in which Expr value is cached */
    } u;
................................................................................
  int nMem;            /* Number of memory cells used so far */
  int nOpAlloc;        /* Number of slots allocated for Vdbe.aOp[] */
  int szOpAlloc;       /* Bytes of memory space allocated for Vdbe.aOp[] */
  int iSelfTab;        /* Table associated with an index on expr, or negative
                       ** of the base register during check-constraint eval */
  int nLabel;          /* Number of labels used */
  int *aLabel;         /* Space to hold the labels */
  ExprList *pConstExpr;/* Constant expressions */
  Token constraintName;/* Name of the constraint currently being parsed */
  yDbMask writeMask;   /* Start a write transaction on these databases */
  yDbMask cookieMask;  /* Bitmask of schema verified databases */
  int regRowid;        /* Register holding rowid of CREATE TABLE entry */
  int regRoot;         /* Register holding root page number for new objects */
  int nMaxArg;         /* Max args passed to user function by sub-program */
  int nSelect;         /* Number of SELECT stmts. Counter for Select.selId */







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  struct ExprList_item { /* For each expression in the list */
    Expr *pExpr;            /* The parse tree for this expression */
    char *zName;            /* Token associated with this expression */
    char *zSpan;            /* Original text of the expression */
    u8 sortOrder;           /* 1 for DESC or 0 for ASC */
    unsigned done :1;       /* A flag to indicate when processing is finished */
    unsigned bSpanIsTab :1; /* zSpan holds DB.TABLE.COLUMN */
    unsigned reusable   :1; /* Constant expression is reusable */
    unsigned bSorterRef :1; /* Defer evaluation until after sorting */
    unsigned bAuxSubrtn :1; /* Member of pAuxExpr to be coded as a subroutine */
    union {
      struct {
        u16 iOrderByCol;      /* For ORDER BY, column number in result set */
        u16 iAlias;           /* Index into Parse.aAlias[] for zName */
      } x;
      int iConstExprReg;      /* Register in which Expr value is cached */
    } u;
................................................................................
  int nMem;            /* Number of memory cells used so far */
  int nOpAlloc;        /* Number of slots allocated for Vdbe.aOp[] */
  int szOpAlloc;       /* Bytes of memory space allocated for Vdbe.aOp[] */
  int iSelfTab;        /* Table associated with an index on expr, or negative
                       ** of the base register during check-constraint eval */
  int nLabel;          /* Number of labels used */
  int *aLabel;         /* Space to hold the labels */
  ExprList *pAuxExpr;  /* Exprs coded at initialization or as subroutines */
  Token constraintName;/* Name of the constraint currently being parsed */
  yDbMask writeMask;   /* Start a write transaction on these databases */
  yDbMask cookieMask;  /* Bitmask of schema verified databases */
  int regRowid;        /* Register holding rowid of CREATE TABLE entry */
  int regRoot;         /* Register holding root page number for new objects */
  int nMaxArg;         /* Max args passed to user function by sub-program */
  int nSelect;         /* Number of SELECT stmts. Counter for Select.selId */