database/sqlite
1
0
Fork 0
mirror of https://github.com/sqlite/sqlite.git synced 2025-11-12 13:01:09 +03:00
Code Activity

Be more aggressive in optimizing constant conditional expressions.

Browse Source 
FossilOrigin-Name: b7e39851a75b87ebca747b26a39989560fd6362b
This commit is contained in:
drh
2014-01-02 17:57:16 +00:00
parent b00d862139
commit 991a198511
3 changed files with 41 additions and 20 deletions
Download Patch File Download Diff File Expand all files Collapse all files

47
src/expr.c
View File

@@ -523,16 +523,25 @@ Expr *sqlite3PExpr(
}
/*
** Return 1 if an expression must be FALSE in all cases and 0 if the
** expression might be true. This is an optimization. If is OK to
** return 0 here even if the expression really is always false (a
** false negative). But it is a bug to return 1 if the expression
** might be true in some rare circumstances (a false positive.)
** If the expression is always either TRUE or FALSE (respectively),
** then return 1. If one cannot determine the truth value of the
** expression at compile-time return 0.
**
** This is an optimization. If is OK to return 0 here even if
** the expression really is always false or false (a false negative).
** But it is a bug to return 1 if the expression might have different
** boolean values in different circumstances (a false positive.)
**
** Note that if the expression is part of conditional for a
** LEFT JOIN, then we cannot determine at compile-time whether or not
** is it true or false, so always return 0.
*/
static int exprAlwaysTrue(Expr *p){
int v = 0;
if( ExprHasProperty(p, EP_FromJoin) ) return 0;
if( !sqlite3ExprIsInteger(p, &v) ) return 0;
return v!=0;
}
static int exprAlwaysFalse(Expr *p){
int v = 0;
if( ExprHasProperty(p, EP_FromJoin) ) return 0;
@@ -3614,10 +3623,16 @@ void sqlite3ExprIfTrue(Parse *pParse, Expr *pExpr, int dest, int jumpIfNull){
}
#endif
default: {
r1 = sqlite3ExprCodeTemp(pParse, pExpr, &regFree1);
sqlite3VdbeAddOp3(v, OP_If, r1, dest, jumpIfNull!=0);
testcase( regFree1==0 );
testcase( jumpIfNull==0 );
if( exprAlwaysTrue(pExpr) ){
sqlite3VdbeAddOp2(v, OP_Goto, 0, dest);
}else if( exprAlwaysFalse(pExpr) ){
/* No-op */
}else{
r1 = sqlite3ExprCodeTemp(pParse, pExpr, &regFree1);
sqlite3VdbeAddOp3(v, OP_If, r1, dest, jumpIfNull!=0);
testcase( regFree1==0 );
testcase( jumpIfNull==0 );
}
break;
}
}
@@ -3759,10 +3774,16 @@ void sqlite3ExprIfFalse(Parse *pParse, Expr *pExpr, int dest, int jumpIfNull){
}
#endif
default: {
r1 = sqlite3ExprCodeTemp(pParse, pExpr, &regFree1);
sqlite3VdbeAddOp3(v, OP_IfNot, r1, dest, jumpIfNull!=0);
testcase( regFree1==0 );
testcase( jumpIfNull==0 );
if( exprAlwaysFalse(pExpr) ){
sqlite3VdbeAddOp2(v, OP_Goto, 0, dest);
}else if( exprAlwaysTrue(pExpr) ){
/* no-op */
}else{
r1 = sqlite3ExprCodeTemp(pParse, pExpr, &regFree1);
sqlite3VdbeAddOp3(v, OP_IfNot, r1, dest, jumpIfNull!=0);
testcase( regFree1==0 );
testcase( jumpIfNull==0 );
}
break;
}
}