compiler: Add various performance optimization variants

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 97.20497% with 9 lines in your changes missing coverage. Please review.

Project coverage is 87.09%. Comparing base (40b081e) to head (b1a10ee). Report is 17 commits behind head on master.

Files with missing lines	Patch %	Lines
devito/core/operator.py	66.66%	1 Missing and 1 partial :warning:
devito/ir/support/utils.py	50.00%	2 Missing :warning:
devito/passes/clusters/cse.py	98.58%	1 Missing and 1 partial :warning:
devito/passes/clusters/factorization.py	93.54%	2 Missing :warning:
devito/ir/clusters/visitors.py	66.66%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #2446 +/- ## ========================================== + Coverage 87.04% 87.09% +0.04% ========================================== Files 237 238 +1 Lines 44998 45106 +108 Branches 8372 8405 +33 ========================================== + Hits 39167 39283 +116 + Misses 5102 5091 -11 - Partials 729 732 +3 ```

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