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A new implementation for the sqlite3ExprImpliesExpr() theorem prover that

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does a better job of answering TRUE to "(NOT A) OR B" when B is a NOT NULL
expression.

FossilOrigin-Name: b3413197f57711f04102d8cc6ff1e8ddbe0f5f2bcb6e1989cf314fa97f0ff7f1
This commit is contained in:
drh
2019-05-11 19:36:03 +00:00
parent c6824c8d6c
commit c51cf8642f
3 changed files with 80 additions and 16 deletions
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80
src/expr.c
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@@ -4908,6 +4908,76 @@ int sqlite3ExprCompareSkip(Expr *pA, Expr *pB, int iTab){
iTab);
}
/*
** Return non-zero if Expr p can only be true if pNN is not NULL.
*/
static int exprImpliesNotNull(
Parse *pParse, /* Parsing context */
Expr *p, /* The expression to be checked */
Expr *pNN, /* The expression that is NOT NULL */
int iTab, /* Table being evaluated */
int seenNot /* True if p is an operand of NOT */
){
assert( p );
assert( pNN );
if( sqlite3ExprCompare(pParse, p, pNN, iTab)==0 ) return 1;
switch( p->op ){
case TK_IN: {
if( seenNot && ExprHasProperty(p, EP_xIsSelect) ) return 0;
assert( ExprHasProperty(p,EP_xIsSelect)
|| (p->x.pList!=0 && p->x.pList->nExpr>0) );
return exprImpliesNotNull(pParse, p->pLeft, pNN, iTab, seenNot);
}
case TK_BETWEEN: {
ExprList *pList = p->x.pList;
assert( pList!=0 );
assert( pList->nExpr==2 );
if( seenNot ) return 0;
if( exprImpliesNotNull(pParse, pList->a[0].pExpr, pNN, iTab, seenNot)
|| exprImpliesNotNull(pParse, pList->a[1].pExpr, pNN, iTab, seenNot)
){
return 1;
}
return exprImpliesNotNull(pParse, p->pLeft, pNN, iTab, seenNot);
}
case TK_EQ:
case TK_NE:
case TK_LT:
case TK_LE:
case TK_GT:
case TK_GE:
case TK_PLUS:
case TK_MINUS:
case TK_STAR:
case TK_REM:
case TK_BITAND:
case TK_BITOR:
case TK_SLASH:
case TK_LSHIFT:
case TK_RSHIFT:
case TK_CONCAT: {
if( exprImpliesNotNull(pParse, p->pRight, pNN, iTab, seenNot) ) return 1;
/* Fall thru into the next case */
}
case TK_SPAN:
case TK_COLLATE:
case TK_BITNOT:
case TK_UPLUS:
case TK_UMINUS: {
return exprImpliesNotNull(pParse, p->pLeft, pNN, iTab, seenNot);
}
case TK_TRUTH: {
if( seenNot ) return 0;
if( p->op2!=TK_IS ) return 0;
return exprImpliesNotNull(pParse, p->pLeft, pNN, iTab, seenNot);
}
case TK_NOT: {
return exprImpliesNotNull(pParse, p->pLeft, pNN, iTab, 1);
}
}
return 0;
}
/*
** Return true if we can prove the pE2 will always be true if pE1 is
** true. Return false if we cannot complete the proof or if pE2 might
@@ -4944,15 +5014,9 @@ int sqlite3ExprImpliesExpr(Parse *pParse, Expr *pE1, Expr *pE2, int iTab){
return 1;
}
if( pE2->op==TK_NOTNULL
&& pE1->op!=TK_ISNULL
&& pE1->op!=TK_IS
&& pE1->op!=TK_ISNOT
&& pE1->op!=TK_OR
&& pE1->op!=TK_CASE
&& exprImpliesNotNull(pParse, pE1, pE2->pLeft, iTab, 0)
){
Expr *pX = sqlite3ExprSkipCollate(pE1->pLeft);
testcase( pX!=pE1->pLeft );
if( sqlite3ExprCompare(pParse, pX, pE2->pLeft, iTab)==0 ) return 1;
return 1;
}
return 0;
}