[llvm] [VPlan] Add VPIRBasicBlock, use to model pre-preheader. (PR #93398)

[Florian Hahn via llvm-commits]

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@@ -2951,6 +2960,50 @@ class VPBasicBlock : public VPBlockBase {
   BasicBlock *createEmptyBasicBlock(VPTransformState::CFGState &CFG);
 };
 
+/// A special type of VPBasicBlock that wraps an existing IR basic block.
+/// Recipes of the block get added before the terminator of the wrapped IR basic
+/// block.
+class VPIRWrapperBlock : public VPBasicBlock {
+  BasicBlock *WrappedBlock;
+
+public:
+  VPIRWrapperBlock(BasicBlock *WrappedBlock)
+      : VPBasicBlock(VPIRWrapperBlockSC, WrappedBlock->getName()),
+        WrappedBlock(WrappedBlock) {}
+
+  ~VPIRWrapperBlock() override {}
+
+  static inline bool classof(const VPBlockBase *V) {
+    return V->getVPBlockID() == VPBlockBase::VPIRWrapperBlockSC;
+  }
+
+#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
+  /// Print this VPBsicBlock to \p O, prefixing all lines with \p Indent. \p
+  /// SlotTracker is used to print unnamed VPValue's using consequtive numbers.
+  ///
+  /// Note that the numbering is applied to the whole VPlan, so printing
+  /// individual blocks is consistent with the whole VPlan printing.
+  void print(raw_ostream &O, const Twine &Indent,
+             VPSlotTracker &SlotTracker) const override;
+  using VPBlockBase::print; // Get the print(raw_stream &O) version.
+#endif
+  /// The method which generates the output IR instructions that correspond to
+  /// this VPBasicBlock, thereby "executing" the VPlan.
+  void execute(VPTransformState *State) override;
+
+  VPIRWrapperBlock *clone() override {
+    auto *NewBlock = new VPIRWrapperBlock(WrappedBlock);
+    for (VPRecipeBase &R : *this)
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fhahn wrote:

Recipes is private, can move to protected?

https://github.com/llvm/llvm-project/pull/93398