[llvm] [VPlan] Remove no-op SCALAR-STEPS after unrolling. (PR #123655)

[David Sherwood via llvm-commits]

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@@ -3593,6 +3597,9 @@ class VPlan {
     UFs.insert(UF);
   }
 
+  /// Returns true if the VPlan already has been unrolled, i.e. it has UF = 1.
+  unsigned isUnrolled() const { return UFs.size() == 1 && UFs.back() == 1; }
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david-arm wrote:

Should this return a `bool`?

https://github.com/llvm/llvm-project/pull/123655