[llvm] [LoopVectorize] Add support for vectorisation of simple early exit loops (PR #88385)

[David Sherwood via llvm-commits]

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@@ -696,6 +721,17 @@ class LoopAccessInfo {
   /// Cache the result of analyzeLoop.
   bool CanVecMem = false;
   bool HasConvergentOp = false;
+  bool LoopMayFault = false;
+
+  /// Keeps track of the early-exiting block, if present.
+  BasicBlock *SpeculativeEarlyExitingBB = nullptr;
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david-arm wrote:

In a sense though that is not far off the truth, because when vectorising the loop we are by definition reading ahead in memory which could potentially cause a fault where the scalar loop would not. However, the main reason I added the word 'Speculative' was to distinguish between early exits with exact exit-not-taken counts (which the vectoriser does support) and early exits that cannot be counted.

I'd prefer not to call it `EarlyExitingBB` to avoid any possible confusion, but I'm happy to take suggestions on alternative names that are better? Perhaps `UncountableEarlyExitingBB`?

https://github.com/llvm/llvm-project/pull/88385