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

[Graham Hunter via llvm-commits]

================
@@ -407,16 +414,26 @@ class LoopVectorizationLegality {
     return LAI->getDepChecker().getMaxSafeVectorWidthInBits();
   }
 
+  /// Returns information about whether this loop contains at least one
+  /// uncountable early exit, and if so, if it also contains instructions (such
+  /// as stores) that cause side-effects.
+  UncountableEarlyExitDetail getUncountableEarlyExitDetail() const {
----------------
huntergr-arm wrote:

While we can move the legality checks here, that's more refactoring than I was bargaining on at this stage.

I have added a check to make sure we don't have store recipes in a ReadOnly uncountable exit loop before processing the exits.

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