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Code generator tries to avoid pointless OP_IsNull and OP_Affinity opcodes.

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FossilOrigin-Name: ebb0c8a3e977dc741704e733b5a5d931d9b27028
This commit is contained in:
drh
2009-11-17 18:31:47 +00:00
parent 68ff78b1b0
commit 039fc32e84
6 changed files with 156 additions and 49 deletions
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65
src/expr.c
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@@ -1258,6 +1258,71 @@ int sqlite3ExprIsInteger(Expr *p, int *pValue){
return rc;
}
/*
** Return FALSE if there is no chance that the expression can be NULL.
**
** If the expression might be NULL or if the expression is too complex
** to tell return TRUE.
**
** This routine is used as an optimization, to skip OP_IsNull opcodes
** when we know that a value cannot be NULL. Hence, a false positive
** (returning TRUE when in fact the expression can never be NULL) might
** be a small performance hit but is otherwise harmless. On the other
** hand, a false negative (returning FALSE when the result could be NULL)
** will likely result in an incorrect answer. So when in doubt, return
** TRUE.
*/
int sqlite3ExprCanBeNull(const Expr *p){
u8 op;
while( p->op==TK_UPLUS || p->op==TK_MINUS ){ p = p->pLeft; }
op = p->op;
if( op==TK_REGISTER ) op = p->op2;
switch( op ){
case TK_INTEGER:
case TK_STRING:
case TK_FLOAT:
case TK_BLOB:
return 0;
default:
return 1;
}
}
/*
** Return TRUE if the given expression is a constant which would be
** unchanged by OP_Affinity with the affinity given in the second
** argument.
**
** This routine is used to determine if the OP_Affinity operation
** can be omitted. When in doubt return FALSE. A false negative
** is harmless. A false positive, however, can result in the wrong
** answer.
*/
int sqlite3ExprNeedsNoAffinityChange(const Expr *p, char aff){
u8 op;
if( aff==SQLITE_AFF_NONE ) return 1;
while( p->op==TK_UPLUS || p->op==TK_MINUS ){ p = p->pLeft; }
op = p->op;
if( op==TK_REGISTER ) op = p->op2;
switch( op ){
case TK_INTEGER: {
return aff==SQLITE_AFF_INTEGER || aff==SQLITE_AFF_NUMERIC;
}
case TK_FLOAT: {
return aff==SQLITE_AFF_REAL || aff==SQLITE_AFF_NUMERIC;
}
case TK_STRING: {
return aff==SQLITE_AFF_TEXT;
}
case TK_BLOB: {
return 1;
}
default: {
return 0;
}
}
}
/*
** Return TRUE if the given string is a row-id column name.
*/