[llvm] [VPlan] Add VPPhiAccessors to provide interface for phi recipes (NFC) (PR #129388)

[Florian Hahn via llvm-commits]

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@@ -1085,6 +1085,62 @@ class VPIRInstruction : public VPRecipeBase {
   void extractLastLaneOfOperand(VPBuilder &Builder);
 };
 
+/// Helper type to provide functions to access incoming values and blocks for
+/// phi-like recipes. RecipeTy must be a sub-class of VPRecipeBase.
+template <typename RecipeTy> class VPPhiAccessors {
+  /// Return a VPRecipeBase* to the current object.
+  const VPRecipeBase *getAsRecipe() const {
+    return static_cast<const RecipeTy *>(this);
+  }
+
+public:
+  /// Returns the \p I th incoming VPValue.
+  VPValue *getIncomingValue(unsigned I) const {
+    return getAsRecipe()->getOperand(I);
+  }
+
+  /// Returns an interator range over the incoming values
+  VPUser::const_operand_range incoming_values() const {
+    return getAsRecipe()->operands();
+  }
+
+  /// Returns the \p I th incoming block.
+  const VPBasicBlock *getIncomingBlock(unsigned Idx) const;
+
+  using const_incoming_block_iterator =
+      mapped_iterator<detail::index_iterator,
+                      std::function<const VPBasicBlock *(size_t)>>;
+  using const_incoming_blocks_range =
+      iterator_range<const_incoming_block_iterator>;
+
+  const_incoming_block_iterator incoming_block_begin() const {
+    return const_incoming_block_iterator(
+        detail::index_iterator(0),
+        [this](size_t Idx) { return getIncomingBlock(Idx); });
+  }
+  const_incoming_block_iterator incoming_block_end() const {
+    return const_incoming_block_iterator(
+        detail::index_iterator(getAsRecipe()->getVPDefID() ==
+                                       VPDef::VPWidenIntOrFpInductionSC
+                                   ? 2
+                                   : getAsRecipe()->getNumOperands()),
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fhahn wrote:

I removed it for now, will add more uses in follow-up patches 

https://github.com/llvm/llvm-project/pull/129388