[llvm] [VPlan] Make canonical IV part of the region (PR #156262)

[via llvm-commits]

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@@ -3973,6 +3907,11 @@ class VPWidenCanonicalIVRecipe : public VPSingleDefRecipe,
     return 0;
   }
 
+  /// Return the canonical IV being widened.
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ayalz wrote:

Worth noting that this method must be used only when the enclosing loop region is available, as no region value survives afterwards; i.e., the cast will fail.

https://github.com/llvm/llvm-project/pull/156262