*: simplify LIKE patterns with multiple consecutive wildcards (#17490)

[ti-srebot]

cherry-pick #17490 to release-4.0
You can switch your code base to this Pull Request by using git-extras:

# In tidb repo:
git pr https://github.com/pingcap/tidb/pull/22572

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git push [email protected]:ti-srebot/tidb.git pr/22572:release-4.0-c84aa7997095

---

What problem does this PR solve?

Problem Summary: %% => % and %_ => _% are valid rewrite rules that improve pattern matching performance.

This is a follow up to #17418 (comment) (cc @wjhuang2016).

What is changed and how it works?

What's Changed:

• LIKE pattern compile now applies the rules %% => % and %_ => _%.

Related changes

Preceding: #17418

Check List

Tests

• Unit test

Moderate performance improvement for the affected cases:

name                                 old time/op  new time/op  delta
DoMatch/a%_%_%_%_b-8                 31.0ns ± 0%  20.2ns ± 0%   ~     (p=1.000 n=1+1)
DoMatch/%_%_a%_%_b-8                 37.1ns ± 0%  26.2ns ± 0%   ~     (p=1.000 n=1+1)
DoMatch/a%_%_a%_%_b-8                 142ns ± 0%    94ns ± 0%   ~     (p=1.000 n=1+1)
DoMatchNegative/a%a%a%a%a%a%a%a%b-8   193ns ± 0%   171ns ± 0%   ~     (p=1.000 n=1+1)

Release note

• Simplify LIKE patterns with multiple consecutive wildcards.

[ti-srebot]

/run-all-tests

[ti-srebot]

@zz-jason please accept the invitation then you can push to the cherry-pick pull requests.
https://github.com/ti-srebot/tidb/invitations

[xiongjiwei]

this PR not only improve performance, but also fix a bug

mysql> select 'aa' collate utf8mb4_general_ci like 'a_%a';
+---------------------------------------------+
| 'aa' collate utf8mb4_general_ci like 'a_%a' |
+---------------------------------------------+
|                                           0 |
+---------------------------------------------+
1 row in set (0.06 sec)

this test case is added in PR #22558

[xiongjiwei]

/run-all-tests

[xiongjiwei]

Sorry, make a mistake. This PR not fix the bug.

[ti-chi-bot]

@ti-srebot: PR needs rebase.

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[xiongjiwei]

/close

[ti-chi-bot]

@xiongjiwei: Closed this PR.

In response to this:

/close

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