[llvm] [VPlan] Implement VPlan-based unit-strideness speculation (PR #182595)

[Luke Lau via llvm-commits]

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@@ -264,6 +264,11 @@ class VPSCEVExpander {
   /// Try to expand \p S into recipes and live-ins using the builder. Returns
   /// nullptr if \p S cannot be expanded yet.
   VPValue *tryToExpand(const SCEV *S);
+
+  /// Try to expand \p Pred into recipes and live-ins using the builder. Returns
+  /// nullptr if \p Pred cannot be expanded (not expected to happen for the
+  /// predicates we currently generate).
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lukel97 wrote:

Nit, this is already documented at the call site, I don't think we need to mention it here
```suggestion
  /// nullptr if \p Pred cannot be expanded yet.
```

https://github.com/llvm/llvm-project/pull/182595