[llvm] [LV] Ignore some costs when loop gets fully unrolled (PR #106699)

[Florian Hahn via llvm-commits]

================
@@ -2663,6 +2663,33 @@ static Value *getExpandedStep(const InductionDescriptor &ID,
   return I->second;
 }
 
+/// Knowing that loop \p L would be fully unrolled after vectorisation, add
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fhahn wrote:

```suggestion
/// Knowing that loop \p L executes a single vector iteration, add
```

Might be more accurate, as the branch gets removed and to avoid confusion with VPlan2VPlan unrolling

https://github.com/llvm/llvm-project/pull/106699