compiler: Tweak fission for parallelism

[FabioLuporini]

No description provided.

[codecov]

Codecov Report

❌ Patch coverage is 27.27273% with 8 lines in your changes missing coverage. Please review.
✅ Project coverage is 53.22%. Comparing base (59c357b) to head (bc2281c).

Files with missing lines	Patch %	Lines
tests/test_fission.py	11.11%	8 Missing ⚠️

❗ There is a different number of reports uploaded between BASE (59c357b) and HEAD (bc2281c). Click for more details.

HEAD has 8 uploads less than BASE

Flag	BASE (59c357b)	HEAD (bc2281c)
	18	10

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #2793       +/-   ##
===========================================
- Coverage   83.02%   53.22%   -29.81%     
===========================================
  Files         248      248               
  Lines       50804    50813        +9     
  Branches     4479     4479               
===========================================
- Hits        42180    27044    -15136     
- Misses       7857    22801    +14944     
- Partials      767      968      +201     

Flag	Coverage Δ
pytest-gpu-aomp-amdgpuX	68.53% <100.00%> (ø)
pytest-gpu-nvc-nvidiaX	69.04% <100.00%> (ø)

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[EdCaunt]

What's the advantage of working backward through this rather than forward?

Nitpick: I think having the range start at 1, then just having i in the indices was slightly easier to understand