compiler: Misc code generation improvements

[codecov[bot]]

Codecov Report

Attention: 83 lines in your changes are missing coverage. Please review.

Comparison is base (3126fb0) 86.85% compared to head (5f63560) 86.76%.

Files	Patch %	Lines
devito/arch/compiler.py	20.00%	39 Missing and 1 partial :warning:
devito/ir/iet/visitors.py	70.42%	12 Missing and 9 partials :warning:
devito/symbolics/extended_sympy.py	91.25%	2 Missing and 5 partials :warning:
devito/ir/iet/nodes.py	84.61%	5 Missing and 1 partial :warning:
devito/passes/iet/orchestration.py	0.00%	5 Missing :warning:
devito/passes/iet/langbase.py	97.18%	1 Missing and 1 partial :warning:
devito/symbolics/printer.py	66.66%	1 Missing and 1 partial :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #2282 +/- ## ========================================== - Coverage 86.85% 86.76% -0.10% ========================================== Files 229 229 Lines 42584 42884 +300 Branches 7900 7951 +51 ========================================== + Hits 36986 37207 +221 - Misses 4942 5002 +60 - Partials 656 675 +19 ```

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