[llvm] [VPlan] Move IV predicate handling to VPlan. (PR #192876)

[Mel Chen via llvm-commits]

================
@@ -145,6 +145,16 @@ struct VPlanTransforms {
       const SmallPtrSetImpl<const PHINode *> &FixedOrderRecurrences,
       const SmallPtrSetImpl<PHINode *> &InLoopReductions, bool AllowReordering);
 
+  /// Finalize SCEV predicates by adding induction predicates from \p Plan to
+  /// \p PSE and checking constraints. Returns false if predicated IVs have
+  /// outside-loop uses via ExitingIVValue, if SCEV predicate complexity exceeds
+  /// \p SCEVCheckThreshold, or if predicates are needed but \p OptForSize is
+  /// true.
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Mel-Chen wrote:

I'm not sure if my understanding is correct.
```suggestion
  /// Finalize SCEV predicates by adding induction predicates from \p Plan to
  /// \p PSE and checking constraints. 
  /// \returns false if:
  /// - Predicated IVs have outside-loop uses via ExitingIVValue
  /// - SCEV predicate complexity exceeds \p SCEVCheckThreshold
  /// - Predicates are needed but \p OptForSize is true.
```

https://github.com/llvm/llvm-project/pull/192876