[VPlan] Add recipe to handle SCEV expansion (NFC).

This can be used to explicitly model VPValues that depend on SCEV
expansion, like the step for inductions.

Reviewed By: Ayal

Differential Revision: https://reviews.llvm.org/D116288

llvm/lib/Transforms/Vectorize/VPlan.cpp

@@ -41,6 +41,7 @@
 #include "llvm/Support/GraphWriter.h"
 #include "llvm/Support/raw_ostream.h"
 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
+#include "llvm/Transforms/Utils/ScalarEvolutionExpander.h"
 #include <cassert>
 #include <iterator>
 #include <string>
@@ -1399,6 +1400,27 @@ void VPCanonicalIVPHIRecipe::print(raw_ostream &O, const Twine &Indent,
 }
 #endif
 
+void VPExpandSCEVRecipe::execute(VPTransformState &State) {
+  assert(!State.Instance && "cannot be used in per-lane");
+  const DataLayout &DL =
+      State.CFG.VectorPreHeader->getModule()->getDataLayout();
+  SCEVExpander Exp(SE, DL, "induction");
+  Value *Res = Exp.expandCodeFor(Expr, Expr->getType(),
+                                 State.CFG.VectorPreHeader->getTerminator());
+
+  for (unsigned Part = 0, UF = State.UF; Part < UF; ++Part)
+    State.set(this, Res, Part);
+}
+
+#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
+void VPExpandSCEVRecipe::print(raw_ostream &O, const Twine &Indent,
+                               VPSlotTracker &SlotTracker) const {
+  O << Indent << "EMIT ";
+  getVPSingleValue()->printAsOperand(O, SlotTracker);
+  O << " = EXPAND SCEV " << *Expr;
+}
+#endif
+
 void VPWidenCanonicalIVRecipe::execute(VPTransformState &State) {
   Value *CanonicalIV = State.get(getOperand(0), 0);
   Type *STy = CanonicalIV->getType();

llvm/lib/Transforms/Vectorize/VPlan.h

@@ -1720,6 +1720,36 @@ public:
   }
 };
 
+/// Recipe to expand a SCEV expression.
+/// TODO: Currently the recipe always expands the expression in the loop
+/// pre-header, but the recipe is currently placed in the header; place it in
+/// the pre-header once the latter is modeled in VPlan as a VPBasicBlock.
+class VPExpandSCEVRecipe : public VPRecipeBase, public VPValue {
+  const SCEV *Expr;
+  ScalarEvolution &SE;
+
+public:
+  VPExpandSCEVRecipe(const SCEV *Expr, ScalarEvolution &SE)
+      : VPRecipeBase(VPExpandSCEVSC, {}), VPValue(nullptr, this), Expr(Expr),
+        SE(SE) {}
+
+  ~VPExpandSCEVRecipe() override = default;
+
+  /// Method to support type inquiry through isa, cast, and dyn_cast.
+  static inline bool classof(const VPDef *D) {
+    return D->getVPDefID() == VPExpandSCEVSC;
+  }
+
+  /// Generate a canonical vector induction variable of the vector loop, with
+  void execute(VPTransformState &State) override;
+
+#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
+  /// Print the recipe.
+  void print(raw_ostream &O, const Twine &Indent,
+             VPSlotTracker &SlotTracker) const override;
+#endif
+};
+
 /// Canonical scalar induction phi of the vector loop. Starting at the specified
 /// start value (either 0 or the resume value when vectorizing the epilogue
 /// loop). VPWidenCanonicalIVRecipe represents the vector version of the

llvm/lib/Transforms/Vectorize/VPlanValue.h

@@ -327,6 +327,7 @@ public:
   /// type identification.
   using VPRecipeTy = enum {
     VPBranchOnMaskSC,
+    VPExpandSCEVSC,
     VPInstructionSC,
     VPInterleaveSC,
     VPReductionSC,