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Overview
Comment:Optimization to the ExprList object to make it slightly smaller and faster.
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SHA3-256: 4da49a95c0f07ed7790169e8833c3e2dacda504a3d997f567572020148abe30b
User & Date: drh 2017-09-15 15:17:48
References
2017-09-17
19:45
Do not make the assumption (as check-in [4da49a95c0f07] incorrectly did) that the ExprList returned by sqlite3ExprListDup() would never be passed into sqlite3ExprListAppend(). Include a new test case that shows this sometimes does happen. check-in: 29227d00 user: drh tags: trunk
Context
2017-09-15
15:38
Improved the header-comment documentation on sqlite3ExprCodeExprList(). No changes to code. check-in: 5dc3ecb5 user: drh tags: trunk
15:17
Optimization to the ExprList object to make it slightly smaller and faster. check-in: 4da49a95 user: drh tags: trunk
14:36
Fix a harmless comment typo. No changes to code. check-in: f7f0bf1d user: drh tags: trunk
Changes
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Changes to src/expr.c.

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  int i;
  Expr *pPriorSelectCol = 0;
  assert( db!=0 );
  if( p==0 ) return 0;
  pNew = sqlite3DbMallocRawNN(db, 
             sizeof(*pNew)+sizeof(pNew->a[0])*(p->nExpr-1) );
  if( pNew==0 ) return 0;
  pNew->nAlloc = pNew->nExpr = p->nExpr;




  pItem = pNew->a;
  pOldItem = p->a;
  for(i=0; i<p->nExpr; i++, pItem++, pOldItem++){
    Expr *pOldExpr = pOldItem->pExpr;
    Expr *pNewExpr;
    pItem->pExpr = sqlite3ExprDup(db, pOldExpr, flags);
    if( pOldExpr 
................................................................................
#endif


/*
** Add a new element to the end of an expression list.  If pList is
** initially NULL, then create a new expression list.
**







** If a memory allocation error occurs, the entire list is freed and
** NULL is returned.  If non-NULL is returned, then it is guaranteed
** that the new entry was successfully appended.
*/
ExprList *sqlite3ExprListAppend(
  Parse *pParse,          /* Parsing context */
  ExprList *pList,        /* List to which to append. Might be NULL */
  Expr *pExpr             /* Expression to be appended. Might be NULL */
){
  struct ExprList_item *pItem;
  sqlite3 *db = pParse->db;
  assert( db!=0 );

  if( pList==0 ){
    pList = sqlite3DbMallocRawNN(db, sizeof(ExprList) );
    if( pList==0 ){
      goto no_mem;
    }
    pList->nExpr = 0;
    pList->nAlloc = 1;
  }else if( pList->nExpr==pList->nAlloc ){
    ExprList *pNew;
    pNew = sqlite3DbRealloc(db, pList, 
             sizeof(*pList)+(2*pList->nAlloc - 1)*sizeof(pList->a[0]));
    if( pNew==0 ){
      goto no_mem;
    }
    pList = pNew;
    pList->nAlloc *= 2;
  }
  pItem = &pList->a[pList->nExpr++];
  assert( offsetof(struct ExprList_item,zName)==sizeof(pItem->pExpr) );
  assert( offsetof(struct ExprList_item,pExpr)==0 );
  memset(&pItem->zName,0,sizeof(*pItem)-offsetof(struct ExprList_item,zName));
  pItem->pExpr = pExpr;
  return pList;







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  int i;
  Expr *pPriorSelectCol = 0;
  assert( db!=0 );
  if( p==0 ) return 0;
  pNew = sqlite3DbMallocRawNN(db, 
             sizeof(*pNew)+sizeof(pNew->a[0])*(p->nExpr-1) );
  if( pNew==0 ) return 0;
  pNew->nExpr = p->nExpr;
  /* After being duplicated, the ExprList may not be expanded again using
  ** Append() because Append() assumes that the number of slots in
  ** ExprList.a[] is a power of 2 */
  VVA_ONLY( pNew->bFixedSize = 1 );
  pItem = pNew->a;
  pOldItem = p->a;
  for(i=0; i<p->nExpr; i++, pItem++, pOldItem++){
    Expr *pOldExpr = pOldItem->pExpr;
    Expr *pNewExpr;
    pItem->pExpr = sqlite3ExprDup(db, pOldExpr, flags);
    if( pOldExpr 
................................................................................
#endif


/*
** Add a new element to the end of an expression list.  If pList is
** initially NULL, then create a new expression list.
**
** The pList argument must be either NULL or a pointer to an ExprList
** obtained from a prior call to sqlite3ExprListAppend().  This routine
** may not be used with an ExprList obtained from sqlite3ExprListDup().
** Reason:  This routine assumes that the number of slots in pList->a[]
** is a power of two.  That is true for sqlite3ExprListAppend() returns
** but is not necessarily true from the return value of sqlite3ExprListDup().
**
** If a memory allocation error occurs, the entire list is freed and
** NULL is returned.  If non-NULL is returned, then it is guaranteed
** that the new entry was successfully appended.
*/
ExprList *sqlite3ExprListAppend(
  Parse *pParse,          /* Parsing context */
  ExprList *pList,        /* List to which to append. Might be NULL */
  Expr *pExpr             /* Expression to be appended. Might be NULL */
){
  struct ExprList_item *pItem;
  sqlite3 *db = pParse->db;
  assert( db!=0 );
  assert( pList==0 || pList->bFixedSize==0 );
  if( pList==0 ){
    pList = sqlite3DbMallocRawNN(db, sizeof(ExprList) );
    if( pList==0 ){
      goto no_mem;
    }
    pList->nExpr = 0;
    VVA_ONLY( pList->bFixedSize = 0 );
  }else if( (pList->nExpr & (pList->nExpr-1))==0 ){
    ExprList *pNew;
    pNew = sqlite3DbRealloc(db, pList, 
             sizeof(*pList)+(2*pList->nExpr - 1)*sizeof(pList->a[0]));
    if( pNew==0 ){
      goto no_mem;
    }
    pList = pNew;

  }
  pItem = &pList->a[pList->nExpr++];
  assert( offsetof(struct ExprList_item,zName)==sizeof(pItem->pExpr) );
  assert( offsetof(struct ExprList_item,pExpr)==0 );
  memset(&pItem->zName,0,sizeof(*pItem)-offsetof(struct ExprList_item,zName));
  pItem->pExpr = pExpr;
  return pList;

Changes to src/sqliteInt.h.

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** column expression as it exists in a SELECT statement.  However, if
** the bSpanIsTab flag is set, then zSpan is overloaded to mean the name
** of the result column in the form: DATABASE.TABLE.COLUMN.  This later
** form is used for name resolution with nested FROM clauses.
*/
struct ExprList {
  int nExpr;             /* Number of expressions on the list */
  int nAlloc;            /* Number of a[] slots allocated */


  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 */







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** column expression as it exists in a SELECT statement.  However, if
** the bSpanIsTab flag is set, then zSpan is overloaded to mean the name
** of the result column in the form: DATABASE.TABLE.COLUMN.  This later
** form is used for name resolution with nested FROM clauses.
*/
struct ExprList {
  int nExpr;             /* Number of expressions on the list */
#ifdef SQLITE_DEBUG
  u8 bFixedSize;         /* May not be expanded using sqlite3ExprListAppend() */
#endif
  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 */