[VPlan] Set branch weight metadata on middle term in VPlan (NFC)

Manage branch weights for the BranchOnCond in the middle block in VPlan.
This requires updating VPInstruction to inherit from VPIRMetadata, which
in general makes sense as there are a number of opcodes that could take
metadata.

Author: fhahn

llvm/lib/Transforms/Vectorize/LoopVectorize.cpp

@@ -7282,6 +7282,30 @@ static void fixReductionScalarResumeWhenVectorizingEpilog(
       BypassBlock, MainResumePhi->getIncomingValueForBlock(BypassBlock));
 }
 
+/// Add branch weight metadata, if the \p Plan's middle block is terminated by a
+/// BranchOnCond recipe.
+static void addBranchWeigthToMiddleTerminator(VPlan &Plan, ElementCount VF,
+                                              Loop *OrigLoop) {
+  // 4. Adjust branch weight of the branch in the middle block.
+  Instruction *LatchTerm = OrigLoop->getLoopLatch()->getTerminator();
+  if (!hasBranchWeightMD(*LatchTerm))
+    return;
+
+  VPBasicBlock *MiddleVPBB = Plan.getMiddleBlock();
+  auto *MiddleTerm =
+      dyn_cast_or_null<VPInstruction>(MiddleVPBB->getTerminator());
+  if (!MiddleTerm)
+    return;
+
+  // Assume that `Count % VectorTripCount` is equally distributed.
+  unsigned TripCount = Plan.getUF() * VF.getKnownMinValue();
+  assert(TripCount > 0 && "trip count should not be zero");
+  MDBuilder MDB(LatchTerm->getContext());
+  MDNode *BranchWeights =
+      MDB.createBranchWeights({1, TripCount - 1}, /*IsExpected=*/false);
+  MiddleTerm->addMetadata(LLVMContext::MD_prof, BranchWeights);
+}
+
 DenseMap<const SCEV *, Value *> LoopVectorizationPlanner::executePlan(
     ElementCount BestVF, unsigned BestUF, VPlan &BestVPlan,
     InnerLoopVectorizer &ILV, DominatorTree *DT, bool VectorizingEpilogue) {
@@ -7304,11 +7328,8 @@ DenseMap<const SCEV *, Value *> LoopVectorizationPlanner::executePlan(
 
   VPlanTransforms::convertToConcreteRecipes(BestVPlan,
                                             *Legal->getWidestInductionType());
-  // Retrieve and store the middle block before dissolving regions. Regions are
-  // dissolved after optimizing for VF and UF, which completely removes unneeded
-  // loop regions first.
-  VPBasicBlock *MiddleVPBB =
-      BestVPlan.getVectorLoopRegion() ? BestVPlan.getMiddleBlock() : nullptr;
+
+  addBranchWeigthToMiddleTerminator(BestVPlan, BestVF, OrigLoop);
   VPlanTransforms::dissolveLoopRegions(BestVPlan);
   // Perform the actual loop transformation.
   VPTransformState State(&TTI, BestVF, LI, DT, ILV.AC, ILV.Builder, &BestVPlan,
@@ -7451,20 +7472,6 @@ DenseMap<const SCEV *, Value *> LoopVectorizationPlanner::executePlan(
 
   ILV.printDebugTracesAtEnd();
 
-  // 4. Adjust branch weight of the branch in the middle block.
-  if (HeaderVPBB) {
-    auto *MiddleTerm =
-        cast<BranchInst>(State.CFG.VPBB2IRBB[MiddleVPBB]->getTerminator());
-    if (MiddleTerm->isConditional() &&
-        hasBranchWeightMD(*OrigLoop->getLoopLatch()->getTerminator())) {
-      // Assume that `Count % VectorTripCount` is equally distributed.
-      unsigned TripCount = BestVPlan.getUF() * State.VF.getKnownMinValue();
-      assert(TripCount > 0 && "trip count should not be zero");
-      const uint32_t Weights[] = {1, TripCount - 1};
-      setBranchWeights(*MiddleTerm, Weights, /*IsExpected=*/false);
-    }
-  }
-
   return ExpandedSCEVs;
 }
 

llvm/lib/Transforms/Vectorize/VPlan.h

@@ -882,11 +882,39 @@ template <unsigned PartOpIdx> class VPUnrollPartAccessor {
   unsigned getUnrollPart(VPUser &U) const;
 };
 
+/// Helper to manage IR metadata for recipes. It filters out metadata that
+/// cannot be propagated.
+class VPIRMetadata {
+  SmallVector<std::pair<unsigned, MDNode *>> Metadata;
+
+public:
+  VPIRMetadata() {}
+
+  /// Adds metatadata that can be preserved from the original instruction
+  /// \p I.
+  VPIRMetadata(Instruction &I) { getMetadataToPropagate(&I, Metadata); }
+
+  /// Adds metatadata that can be preserved from the original instruction
+  /// \p I and noalias metadata guaranteed by runtime checks using \p LVer.
+  VPIRMetadata(Instruction &I, LoopVersioning *LVer);
+
+  /// Copy constructor for cloning.
+  VPIRMetadata(const VPIRMetadata &Other) : Metadata(Other.Metadata) {}
+
+  /// Add all metadata to \p I.
+  void applyMetadata(Instruction &I) const;
+
+  void addMetadata(unsigned Kind, MDNode *Node) {
+    Metadata.emplace_back(Kind, Node);
+  }
+};
+
 /// This is a concrete Recipe that models a single VPlan-level instruction.
 /// While as any Recipe it may generate a sequence of IR instructions when
 /// executed, these instructions would always form a single-def expression as
 /// the VPInstruction is also a single def-use vertex.
 class VPInstruction : public VPRecipeWithIRFlags,
+                      public VPIRMetadata,
                       public VPUnrollPartAccessor<1> {
   friend class VPlanSlp;
 
@@ -976,7 +1004,7 @@ class VPInstruction : public VPRecipeWithIRFlags,
   VPInstruction(unsigned Opcode, ArrayRef<VPValue *> Operands, DebugLoc DL = {},
                 const Twine &Name = "")
       : VPRecipeWithIRFlags(VPDef::VPInstructionSC, Operands, DL),
-        Opcode(Opcode), Name(Name.str()) {}
+        VPIRMetadata(), Opcode(Opcode), Name(Name.str()) {}
 
   VPInstruction(unsigned Opcode, ArrayRef<VPValue *> Operands,
                 const VPIRFlags &Flags, DebugLoc DL = {},
@@ -1268,29 +1296,6 @@ struct VPIRPhi : public VPIRInstruction, public VPPhiAccessors {
   const VPRecipeBase *getAsRecipe() const override { return this; }
 };
 
-/// Helper to manage IR metadata for recipes. It filters out metadata that
-/// cannot be propagated.
-class VPIRMetadata {
-  SmallVector<std::pair<unsigned, MDNode *>> Metadata;
-
-public:
-  VPIRMetadata() {}
-
-  /// Adds metatadata that can be preserved from the original instruction
-  /// \p I.
-  VPIRMetadata(Instruction &I) { getMetadataToPropagate(&I, Metadata); }
-
-  /// Adds metatadata that can be preserved from the original instruction
-  /// \p I and noalias metadata guaranteed by runtime checks using \p LVer.
-  VPIRMetadata(Instruction &I, LoopVersioning *LVer);
-
-  /// Copy constructor for cloning.
-  VPIRMetadata(const VPIRMetadata &Other) : Metadata(Other.Metadata) {}
-
-  /// Add all metadata to \p I.
-  void applyMetadata(Instruction &I) const;
-};
-
 /// VPWidenRecipe is a recipe for producing a widened instruction using the
 /// opcode and operands of the recipe. This recipe covers most of the
 /// traditional vectorization cases where each recipe transforms into a

llvm/lib/Transforms/Vectorize/VPlanRecipes.cpp

@@ -410,7 +410,7 @@ VPInstruction::VPInstruction(unsigned Opcode, ArrayRef<VPValue *> Operands,
                              const VPIRFlags &Flags, DebugLoc DL,
                              const Twine &Name)
     : VPRecipeWithIRFlags(VPDef::VPInstructionSC, Operands, Flags, DL),
-      Opcode(Opcode), Name(Name.str()) {
+      VPIRMetadata(), Opcode(Opcode), Name(Name.str()) {
   assert(flagsValidForOpcode(getOpcode()) &&
          "Set flags not supported for the provided opcode");
 }
@@ -591,7 +591,9 @@ Value *VPInstruction::generate(VPTransformState &State) {
   }
   case VPInstruction::BranchOnCond: {
     Value *Cond = State.get(getOperand(0), VPLane(0));
-    return createCondBranch(Cond, getParent(), State);
+    auto *Br = createCondBranch(Cond, getParent(), State);
+    applyMetadata(*Br);
+    return Br;
   }
   case VPInstruction::BranchOnCount: {
     // First create the compare.