Early constant folding.

[amosbird]

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For changelog. Remove if this is non-significant change.

Category (leave one):

• Performance Improvement

Short description (up to few sentences):
Run another pass of syntax/expression analysis to get potential optimizations after constant predicates are folded. In preparation of Instant Count()

[amosbird]

Actually we don't need that alias at all, as any references to the original predicate alias (if any) are already dereferenced.

ANALYZE SELECT a
FROM numbers(10)
WHERE (1 = 1) AND (2 = 2) AS a

┌─explain────────────────────────────────────────────────┐
│ SELECT (1 = 1) AND (2 = 2) AS a
FROM numbers(10)
WHERE 1 │
└────────────────────────────────────────────────────────┘

1 rows in set. Elapsed: 0.003 sec.

[alexey-milovidov]

I'd like if you will also add a new test for this PR.

[alexey-milovidov]

Difficult to read - needs careful explanation in comments.

[alexey-milovidov]

Ok, but we also need a performance test.