[llvm] LV]: consider scalable VF during deciding dead epilogue. (PR #156724)

[David Sherwood via llvm-commits]

================
@@ -4407,6 +4407,13 @@ VectorizationFactor LoopVectorizationPlanner::selectEpilogueVectorizationFactor(
     LLVM_DEBUG(dbgs() << "LEV: Maximum Trip Count for Epilogue: "
                       << MaxTripCount << "\n");
   }
+  // Check if the RemainingIterations is scalable.
----------------
david-arm wrote:

Do we actually need this code? Unless I've missed something the only way `RemainingIterations` can be scalable is if both `ScalableTC==true` and `MainLoopVF.isScalable()==true`. Can't you just write

```
  bool ScalableRemIter = ScalableTC && MainLoopVF.isScalable();
```

For all other calculations we are either operating on fixed-width only or we have used estimates for scalable versions.

https://github.com/llvm/llvm-project/pull/156724