compiler: Tweak nofuse mode

[FabioLuporini]

This is not straightforwardly testable in OSS (I tried for 10 mins, but didn't come up with anything)

It is tested via PRO though

It's essentially a performance (not correctness!) bug fix: without this tweak, we might place a few more barriers than strictly necessary. Honestly, maybe just 1-2 at worst, and only in rare cases. But still, patched is better

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 83.03%. Comparing base (f5ce43a) to head (4891ec1).
⚠️ Report is 6 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2790      +/-   ##
==========================================
+ Coverage   82.96%   83.03%   +0.06%     
==========================================
  Files         248      248              
  Lines       50804    50805       +1     
  Branches     4479     4479              
==========================================
+ Hits        42151    42187      +36     
+ Misses       7879     7853      -26     
+ Partials      774      765       -9     

Flag	Coverage Δ
pytest-gpu-aomp-amdgpuX	68.52% <0.00%> (-0.02%)	⬇️
pytest-gpu-nvc-nvidiaX	69.06% <0.00%> (-0.01%)	⬇️

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[FabioLuporini]

closing because unfortunately it's not that straightforward, there's a subtle issue popping up if I do this