[PATCH] D97747: [LoopUnrollRuntime] Add option to unroll loops with at most two exit/exiting blocks.

[Michael Kruse via Phabricator via llvm-commits]

Meinersbur added a comment.

What is the motivation for the switch? Why wouldn't we want to unroll loops with 3 or more exits provided we can and the heuristic sais its profitable? Why is the cutoff at 3? Could we also pass the cutoff-point as an option?



================
Comment at: llvm/lib/Transforms/Utils/LoopUnrollRuntime.cpp:500-503
+  // Only enable unrolling of loops that have at most a single side exit other
+  // than the normal LatchExit.
+  if (OtherExits.size() > 1)
+    return false;
----------------
`OtherExits.size() > 1` will also make the `getTerminatingDeoptimizeCall` heuristic fail, so this is not a semantics change. However, I find the structure confusing, especially if we want to add more conditions that enable the optimization. Did you consider the following structure?

```
if (OtherExits.size() <= 1 && UnrollRuntimeAtMostTwoExits)
  return true;

if (OtherExits.size() == 1 && OtherExits[0]->getTerminatingDeoptimizeCall())
  return true;

// More conditions can be added here
  
return false;
```


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