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Overview
Comment:Simplifications to the expression code generator. Remove about 80 lines of older and obsolete code.
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SHA1: 53f5cfe11516d0496c7760378b6305c3088d479f
User & Date: drh 2010-09-27 18:14:12
References
2011-10-25
20:36
Cherrypick changes [53f5cfe115] and [1f7ef0af8d] in order to fix an issue with DISTINCT check-in: 14bc58ca user: drh tags: branch-3.7.2
Context
2010-09-28
07:14
Merge fixes for ticket [b351d95f9cd5ef17e9d9dbae18f5ca8611190001] into the trunk. check-in: 1f7ef0af user: drh tags: trunk
2010-09-27
21:09
Add assert() statements that fail when a shallow copy is accessed after the original has been modified. These assert() statements should detect the kinds of subtle SCopy bugs such as caused the fault in ticket [b351d95f9cd5ef17e9d9dbae18f]. check-in: 8b8e1732 user: drh tags: bug-b351d95f9c
18:14
Simplifications to the expression code generator. Remove about 80 lines of older and obsolete code. check-in: 53f5cfe1 user: drh tags: trunk
2010-09-25
22:32
Enhance the ANALYZE command so that it gathers statistics in the sqlite_stat1 table even for tables that are empty or have no indices. check-in: a7645d29 user: drh tags: trunk
Changes
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Changes to src/expr.c.

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    int r = p->iReg;
    if( r>=iFrom && r<=iTo ) return 1;    /*NO_TEST*/
  }
  return 0;
}
#endif /* SQLITE_DEBUG || SQLITE_COVERAGE_TEST */

/*
** If the last instruction coded is an ephemeral copy of any of
** the registers in the nReg registers beginning with iReg, then
** convert the last instruction from OP_SCopy to OP_Copy.
*/
void sqlite3ExprHardCopy(Parse *pParse, int iReg, int nReg){
  VdbeOp *pOp;
  Vdbe *v;

  assert( pParse->db->mallocFailed==0 );
  v = pParse->pVdbe;
  assert( v!=0 );
  pOp = sqlite3VdbeGetOp(v, -1);
  assert( pOp!=0 );
  if( pOp->opcode==OP_SCopy && pOp->p1>=iReg && pOp->p1<iReg+nReg ){
    pOp->opcode = OP_Copy;
  }
}

/*
** Generate code to store the value of the iAlias-th alias in register
** target.  The first time this is called, pExpr is evaluated to compute
** the value of the alias.  The value is stored in an auxiliary register
** and the number of that register is returned.  On subsequent calls,
** the register number is returned without generating any code.
**
** Note that in order for this to work, code must be generated in the
** same order that it is executed.
**
** Aliases are numbered starting with 1.  So iAlias is in the range
** of 1 to pParse->nAlias inclusive.  
**
** pParse->aAlias[iAlias-1] records the register number where the value
** of the iAlias-th alias is stored.  If zero, that means that the
** alias has not yet been computed.
*/
static int codeAlias(Parse *pParse, int iAlias, Expr *pExpr, int target){
#if 0
  sqlite3 *db = pParse->db;
  int iReg;
  if( pParse->nAliasAlloc<pParse->nAlias ){
    pParse->aAlias = sqlite3DbReallocOrFree(db, pParse->aAlias,
                                 sizeof(pParse->aAlias[0])*pParse->nAlias );
    testcase( db->mallocFailed && pParse->nAliasAlloc>0 );
    if( db->mallocFailed ) return 0;
    memset(&pParse->aAlias[pParse->nAliasAlloc], 0,
           (pParse->nAlias-pParse->nAliasAlloc)*sizeof(pParse->aAlias[0]));
    pParse->nAliasAlloc = pParse->nAlias;
  }
  assert( iAlias>0 && iAlias<=pParse->nAlias );
  iReg = pParse->aAlias[iAlias-1];
  if( iReg==0 ){
    if( pParse->iCacheLevel>0 ){
      iReg = sqlite3ExprCodeTarget(pParse, pExpr, target);
    }else{
      iReg = ++pParse->nMem;
      sqlite3ExprCode(pParse, pExpr, iReg);
      pParse->aAlias[iAlias-1] = iReg;
    }
  }
  return iReg;
#else
  UNUSED_PARAMETER(iAlias);
  return sqlite3ExprCodeTarget(pParse, pExpr, target);
#endif
}

/*
** Generate code into the current Vdbe to evaluate the given
** expression.  Attempt to store the results in register "target".
** Return the register where results are stored.
**
** With this routine, there is no guarantee that results will
** be stored in target.  The result might be stored in some other
................................................................................
      break;
    }
    case TK_REGISTER: {
      inReg = pExpr->iTable;
      break;
    }
    case TK_AS: {
      inReg = codeAlias(pParse, pExpr->iTable, pExpr->pLeft, target);
      break;
    }
#ifndef SQLITE_OMIT_CAST
    case TK_CAST: {
      /* Expressions of the form:   CAST(pLeft AS token) */
      int aff, to_op;
      inReg = sqlite3ExprCodeTarget(pParse, pExpr->pLeft, target);
................................................................................
){
  struct ExprList_item *pItem;
  int i, n;
  assert( pList!=0 );
  assert( target>0 );
  n = pList->nExpr;
  for(pItem=pList->a, i=0; i<n; i++, pItem++){
    if( pItem->iAlias ){
      int iReg = codeAlias(pParse, pItem->iAlias, pItem->pExpr, target+i);
      Vdbe *v = sqlite3GetVdbe(pParse);
      if( iReg!=target+i ){
        sqlite3VdbeAddOp2(v, OP_SCopy, iReg, target+i);
      }
    }else{
      sqlite3ExprCode(pParse, pItem->pExpr, target+i);
    }
    if( doHardCopy && !pParse->db->mallocFailed ){
      sqlite3ExprHardCopy(pParse, target, n);
    }
  }
  return n;
}

/*
** Generate code for a BETWEEN operator.







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    int r = p->iReg;
    if( r>=iFrom && r<=iTo ) return 1;    /*NO_TEST*/
  }
  return 0;
}
#endif /* SQLITE_DEBUG || SQLITE_COVERAGE_TEST */




































































/*
** Generate code into the current Vdbe to evaluate the given
** expression.  Attempt to store the results in register "target".
** Return the register where results are stored.
**
** With this routine, there is no guarantee that results will
** be stored in target.  The result might be stored in some other
................................................................................
      break;
    }
    case TK_REGISTER: {
      inReg = pExpr->iTable;
      break;
    }
    case TK_AS: {
      inReg = sqlite3ExprCodeTarget(pParse, pExpr->pLeft, target);
      break;
    }
#ifndef SQLITE_OMIT_CAST
    case TK_CAST: {
      /* Expressions of the form:   CAST(pLeft AS token) */
      int aff, to_op;
      inReg = sqlite3ExprCodeTarget(pParse, pExpr->pLeft, target);
................................................................................
){
  struct ExprList_item *pItem;
  int i, n;
  assert( pList!=0 );
  assert( target>0 );
  n = pList->nExpr;
  for(pItem=pList->a, i=0; i<n; i++, pItem++){
    Expr *pExpr = pItem->pExpr;
    int inReg = sqlite3ExprCodeTarget(pParse, pExpr, target+i);
    assert( pParse->pVdbe || pParse->db->mallocFailed );
    if( inReg!=target+i && pParse->pVdbe ){
      sqlite3VdbeAddOp2(pParse->pVdbe, doHardCopy ? OP_Copy : OP_SCopy,


                        inReg, target+i);



    }
  }
  return n;
}

/*
** Generate code for a BETWEEN operator.

Changes to src/sqliteInt.h.

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void sqlite3ExprCodeCopy(Parse*, int, int, int);
void sqlite3ExprCacheStore(Parse*, int, int, int);
void sqlite3ExprCachePush(Parse*);
void sqlite3ExprCachePop(Parse*, int);
void sqlite3ExprCacheRemove(Parse*, int, int);
void sqlite3ExprCacheClear(Parse*);
void sqlite3ExprCacheAffinityChange(Parse*, int, int);
void sqlite3ExprHardCopy(Parse*,int,int);
int sqlite3ExprCode(Parse*, Expr*, int);
int sqlite3ExprCodeTemp(Parse*, Expr*, int*);
int sqlite3ExprCodeTarget(Parse*, Expr*, int);
int sqlite3ExprCodeAndCache(Parse*, Expr*, int);
void sqlite3ExprCodeConstants(Parse*, Expr*);
int sqlite3ExprCodeExprList(Parse*, ExprList*, int, int);
void sqlite3ExprIfTrue(Parse*, Expr*, int, int);







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void sqlite3ExprCodeCopy(Parse*, int, int, int);
void sqlite3ExprCacheStore(Parse*, int, int, int);
void sqlite3ExprCachePush(Parse*);
void sqlite3ExprCachePop(Parse*, int);
void sqlite3ExprCacheRemove(Parse*, int, int);
void sqlite3ExprCacheClear(Parse*);
void sqlite3ExprCacheAffinityChange(Parse*, int, int);

int sqlite3ExprCode(Parse*, Expr*, int);
int sqlite3ExprCodeTemp(Parse*, Expr*, int*);
int sqlite3ExprCodeTarget(Parse*, Expr*, int);
int sqlite3ExprCodeAndCache(Parse*, Expr*, int);
void sqlite3ExprCodeConstants(Parse*, Expr*);
int sqlite3ExprCodeExprList(Parse*, ExprList*, int, int);
void sqlite3ExprIfTrue(Parse*, Expr*, int, int);