Do more aggressive optimization of the AND operator where one side or the
other is always false.
FossilOrigin-Name: f9a7e179cbbeeab5e57bbf392bef89750215546b
diff --git a/src/expr.c b/src/expr.c
index 5e3f120..4751ec9 100644
--- a/src/expr.c
+++ b/src/expr.c
@@ -484,8 +484,14 @@
Expr *pRight, /* Right operand */
const Token *pToken /* Argument token */
){
- Expr *p = sqlite3ExprAlloc(pParse->db, op, pToken, 1);
- sqlite3ExprAttachSubtrees(pParse->db, p, pLeft, pRight);
+ Expr *p;
+ if( op==TK_AND && pLeft && pRight ){
+ /* Take advantage of short-circuit false optimization for AND */
+ p = sqlite3ExprAnd(pParse->db, pLeft, pRight);
+ }else{
+ p = sqlite3ExprAlloc(pParse->db, op, pToken, 1);
+ sqlite3ExprAttachSubtrees(pParse->db, p, pLeft, pRight);
+ }
if( p ) {
sqlite3ExprCheckHeight(pParse, p->nHeight);
}
@@ -493,14 +499,40 @@
}
/*
+** 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.)
+**
+** 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 exprAlwaysFalse(Expr *p){
+ int v = 0;
+ if( ExprHasProperty(p, EP_FromJoin) ) return 0;
+ if( !sqlite3ExprIsInteger(p, &v) ) return 0;
+ return v==0;
+}
+
+/*
** Join two expressions using an AND operator. If either expression is
** NULL, then just return the other expression.
+**
+** If one side or the other of the AND is known to be false, then instead
+** of returning an AND expression, just return a constant expression with
+** a value of false.
*/
Expr *sqlite3ExprAnd(sqlite3 *db, Expr *pLeft, Expr *pRight){
if( pLeft==0 ){
return pRight;
}else if( pRight==0 ){
return pLeft;
+ }else if( exprAlwaysFalse(pLeft) || exprAlwaysFalse(pRight) ){
+ sqlite3ExprDelete(db, pLeft);
+ sqlite3ExprDelete(db, pRight);
+ return sqlite3ExprAlloc(db, TK_INTEGER, &sqlite3IntTokens[0], 0);
}else{
Expr *pNew = sqlite3ExprAlloc(db, TK_AND, 0, 0);
sqlite3ExprAttachSubtrees(db, pNew, pLeft, pRight);