SQLite

The query at the end of the following SQL crashes due to a NULL pointer dereference.

CREATE TABLE t1(aa, bb);
CREATE INDEX t1x1 on t1(abs(aa), abs(bb));
INSERT INTO t1 VALUES(-2,-3),(+2,-3),(-2,+3),(+2,+3);
SELECT * FROM (t1) 
 WHERE ((abs(aa)=1 AND 1=2) OR abs(aa)=2)
   AND abs(bb)=3;

This ticket derives from a separate ticket that was reported against System.Data.SQLite: https://system.data.sqlite.org/index.html/info/b0778fcc041fdca4

Bisecting shows that the problem was introduced for SQLite version 3.20.0 (2017-08-01) by check-in [712267c9c08fdcef] (2017-06-23).

The real problem here is in the optimization of check-in [a47efb7c8520a0111] that tries to make use of expression values pulled from columns of an expression index, rather than recomputing the value of the expression. When processing a multi-index OR clause, the transformations on the expressions to convert them from their original expressions into a reference to the index column become invalid when processing moves on to the next index of a multi-index OR. The solution is to simply disable that optimization for a multi-index OR.

The optimization at [712267c9c08fdcef] that was found by bisect is blameless here, I think. That optimization merely enabled this particular test case to work, and was not the underlying cause of the problem.