opt: simplify contradictory filters to false

[mgartner]

The SimplifySelectFilters normalization rule now transforms filters to
false if any of the filter items are contradictions. This allows
filters to be simplified in more cases, which can trigger other rules.
This can eliminate non-leakproof expressions in filters and allow
SimplifyZeroCardinalityGroup to fire.

For example, consider the query:

SELECT a, b FROM t WHERE a > 0 AND a < 0 AND 1/b = 1

Prior to this commit, it could not be simplified to an empty values
clause because the non-leakproof division operator prevents
SimplifyZeroCardinalityGroup from applying. The normalized plan would
be:

select
 ├── columns: a:1 b:2
 ├── cardinality: [0 - 0]
 ├── immutable
 ├── scan t
 │    └── columns: a:1 b:2
 └── filters
      ├── (a:1 > 0) AND (a:1 < 0) [constraints=(contradiction)]
      └── (1 / b:2) = 1 [outer=(2), immutable]

Now, SimplifySelectFilters eliminates the division operator, making
the expression leakproof, and allowing SimplifyZeroCardinalityGroup to
apply. The normalized plan is now:

values
 ├── columns: a:1!null b:2!null
 ├── cardinality: [0 - 0]
 ├── key: ()
 └── fd: ()-->(1-2)

Release note (performance improvement): The optimizer can detect
contradictory filters in more cases, leading to more efficient query
plans.

[cockroach-teamcity]

This change is 

[DrewKimball]

Nice change! I'm surprised we hadn't been doing this already. I assume this is valid because we make no guarantees about the order in which those filters are evaluated?

Reviewable status: complete! 1 of 0 LGTMs obtained (waiting on @rytaft)

[rytaft]

@DrewKimball that's correct -- see the side-effect policy here: https://github.com/cockroachdb/cockroach/blob/662dd589831c60b2ca929eadc91e9643eb2b3cae/pkg/sql/opt/props/volatility.go

Reviewed 5 of 5 files at r1, all commit messages.
Reviewable status: complete! 2 of 0 LGTMs obtained (waiting on @mgartner)

[mgartner]

TFTRs!

bors r+

[craig]

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[craig]

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