[llvm] [VPlan] Add VPPhiAccessors to provide interface for phi recipes (NFC) (PR #138472)

[Ramkumar Ramachandra via llvm-commits]

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@@ -1224,6 +1224,42 @@ class VPPhiAccessors {
     return getAsRecipe()->getNumOperands();
   }
 
+  /// Returns an interator range over the incoming values.
+  VPUser::const_operand_range incoming_values() const {
+    return make_range(getAsRecipe()->op_begin(),
+                      getAsRecipe()->op_begin() + getNumIncoming());
+  }
+
+  using const_incoming_block_iterator =
+      mapped_iterator<detail::index_iterator,
+                      std::function<const VPBasicBlock *(size_t)>>;
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artagnon wrote:

llvm::functtion_ref?

https://github.com/llvm/llvm-project/pull/138472