[llvm] [NFC][LV] Introduce enums for uncountable exit detail and style (PR #184808)

[Graham Hunter via llvm-commits]

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@@ -77,6 +77,24 @@ typedef unsigned ID;
 
 using VPlanPtr = std::unique_ptr<VPlan>;
 
+// Different methods of handling early exits.
+//
+// For ReadOnlyUncountableExitsInVectorLoop, there are no side effects to worry
+// about, so we can instead process any uncountable exit inside the vector
+// body and branch to an appropriate exit block, matching the behaviour of the
+// scalar loop.
+//
+// For MaskedHandleLastIterationInScalarLoop, all memory operations besides the
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huntergr-arm wrote:

done.

https://github.com/llvm/llvm-project/pull/184808