[llvm] [LoopVectorize] Teach LoopVectorizationLegality about more early exits (PR #107004)

[Paul Walker via llvm-commits]

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@@ -551,6 +589,16 @@ class LoopVectorizationLegality {
   /// (potentially) make a better decision on the maximum VF and enable
   /// the use of those function variants.
   bool VecCallVariantsFound = false;
+
+  /// Indicates whether this loop has a speculative early exit, i.e. an
+  /// uncountable exiting block that is not the latch.
+  bool HasSpeculativeEarlyExit = false;
+
+  /// Keeps track of all the exits with known or countable exit-not-taken
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paulwalker-arm wrote:

Should this be "known or uncountable"? Although if true then doesn't that cover the entire space and thus "Keeps track of all loop exits."  would suffice?

https://github.com/llvm/llvm-project/pull/107004