[LV] Add VPValue operands to VPBlendRecipe (NFCI)

InnerLoopVectorizer's code called during VPlan execution still relies on
original IR's def-use relations to decide which vector code to generate,
limiting VPlan transformations ability to modify def-use relations and still
have ILV generate the vector code.
This commit introduces VPValues for VPBlendRecipe to use as the values to
blend. The recipe is generated with VPValues wrapping the phi's incoming values
of the scalar phi. This reduces ingredient def-use usage by ILV as a step
towards full VPlan-based def-use relations.

Differential Revision: https://reviews.llvm.org/D77539

llvm/lib/Transforms/Vectorize/LoopVectorize.cpp

@@ -6884,17 +6884,18 @@ VPBlendRecipe *VPRecipeBuilder::tryToBlend(Instruction *I, VPlanPtr &Plan) {
   // duplications since this is a simple recursive scan, but future
   // optimizations will clean it up.
 
-  SmallVector<VPValue *, 2> Masks;
+  SmallVector<VPValue *, 2> Operands;
   unsigned NumIncoming = Phi->getNumIncomingValues();
   for (unsigned In = 0; In < NumIncoming; In++) {
     VPValue *EdgeMask =
       createEdgeMask(Phi->getIncomingBlock(In), Phi->getParent(), Plan);
     assert((EdgeMask || NumIncoming == 1) &&
            "Multiple predecessors with one having a full mask");
+    Operands.push_back(Plan->getOrAddVPValue(Phi->getIncomingValue(In)));
     if (EdgeMask)
-      Masks.push_back(EdgeMask);
+      Operands.push_back(EdgeMask);
   }
-  return new VPBlendRecipe(Phi, Masks);
+  return new VPBlendRecipe(Phi, Operands);
 }
 
 VPWidenCallRecipe *
@@ -7436,10 +7437,8 @@ void VPBlendRecipe::execute(VPTransformState &State) {
   // duplications since this is a simple recursive scan, but future
   // optimizations will clean it up.
 
-  unsigned NumIncoming = Phi->getNumIncomingValues();
+  unsigned NumIncoming = getNumIncomingValues();
 
-  assert((User || NumIncoming == 1) &&
-         "Multiple predecessors with predecessors having a full mask");
   // Generate a sequence of selects of the form:
   // SELECT(Mask3, In3,
   //      SELECT(Mask2, In2,
@@ -7449,14 +7448,13 @@ void VPBlendRecipe::execute(VPTransformState &State) {
     for (unsigned Part = 0; Part < State.UF; ++Part) {
       // We might have single edge PHIs (blocks) - use an identity
       // 'select' for the first PHI operand.
-      Value *In0 =
-          State.ILV->getOrCreateVectorValue(Phi->getIncomingValue(In), Part);
+      Value *In0 = State.get(getIncomingValue(In), Part);
       if (In == 0)
         Entry[Part] = In0; // Initialize with the first incoming value.
       else {
         // Select between the current value and the previous incoming edge
         // based on the incoming mask.
-        Value *Cond = State.get(User->getOperand(In), Part);
+        Value *Cond = State.get(getMask(In), Part);
         Entry[Part] =
             State.Builder.CreateSelect(Cond, In0, Entry[Part], "predphi");
       }

llvm/lib/Transforms/Vectorize/VPlan.cpp

@@ -756,17 +756,17 @@ void VPBlendRecipe::print(raw_ostream &O, const Twine &Indent,
   O << " +\n" << Indent << "\"BLEND ";
   Phi->printAsOperand(O, false);
   O << " =";
-  if (!User) {
+  if (getNumIncomingValues() == 1) {
     // Not a User of any mask: not really blending, this is a
     // single-predecessor phi.
     O << " ";
-    Phi->getIncomingValue(0)->printAsOperand(O, false);
+    getIncomingValue(0)->printAsOperand(O, SlotTracker);
   } else {
-    for (unsigned I = 0, E = User->getNumOperands(); I < E; ++I) {
+    for (unsigned I = 0, E = getNumIncomingValues(); I < E; ++I) {
       O << " ";
-      Phi->getIncomingValue(I)->printAsOperand(O, false);
+      getIncomingValue(I)->printAsOperand(O, SlotTracker);
       O << "/";
-      User->getOperand(I)->printAsOperand(O, SlotTracker);
+      getMask(I)->printAsOperand(O, SlotTracker);
     }
   }
   O << "\\l\"";

llvm/lib/Transforms/Vectorize/VPlan.h

@@ -902,24 +902,39 @@ class VPBlendRecipe : public VPRecipeBase {
 private:
   PHINode *Phi;
 
-  /// The blend operation is a User of a mask, if not null.
-  std::unique_ptr<VPUser> User;
+  /// The blend operation is a User of the incoming values and of their
+  /// respective masks, ordered [I0, M0, I1, M1, ...]. Note that a single value
+  /// would be incoming with a full mask for which there is no VPValue.
+  VPUser User;
 
 public:
-  VPBlendRecipe(PHINode *Phi, ArrayRef<VPValue *> Masks)
-      : VPRecipeBase(VPBlendSC), Phi(Phi) {
-    assert((Phi->getNumIncomingValues() == 1 ||
-            Phi->getNumIncomingValues() == Masks.size()) &&
-           "Expected the same number of incoming values and masks");
-    if (!Masks.empty())
-      User.reset(new VPUser(Masks));
+  VPBlendRecipe(PHINode *Phi, ArrayRef<VPValue *> Operands)
+      : VPRecipeBase(VPBlendSC), Phi(Phi), User(Operands) {
+    assert(((Operands.size() == 1) ||
+            (Operands.size() > 2 && Operands.size() % 2 == 0)) &&
+           "Expected either a single incoming value or a greater than two and "
+           "even number of operands");
   }
 
   /// Method to support type inquiry through isa, cast, and dyn_cast.
   static inline bool classof(const VPRecipeBase *V) {
     return V->getVPRecipeID() == VPRecipeBase::VPBlendSC;
   }
 
+  /// Return the number of incoming values, taking into account that a single
+  /// incoming value has no mask.
+  unsigned getNumIncomingValues() const {
+    return (User.getNumOperands() + 1) / 2;
+  }
+
+  /// Return incoming value number \p Idx.
+  VPValue *getIncomingValue(unsigned Idx) const {
+    return User.getOperand(Idx * 2);
+  }
+
+  /// Return mask number \p Idx.
+  VPValue *getMask(unsigned Idx) const { return User.getOperand(Idx * 2 + 1); }
+
   /// Generate the phi/select nodes.
   void execute(VPTransformState &State) override;