Revert "Recommit "[VPlan] First step towards VPlan cost modeling. (llvm#92555)""

This reverts commit 242cc20 and
eea150c, as it is causing a build bot
failure and there have been a number of crashes reported at
llvm#92555

Author: fhahn

llvm/lib/Transforms/Vectorize/LoopVectorizationPlanner.h

@@ -344,16 +344,6 @@ class LoopVectorizationPlanner {
   /// A builder used to construct the current plan.
   VPBuilder Builder;
 
-  /// Computes the cost of \p Plan for vectorization factor \p VF.
-  ///
-  /// The current implementation requires access to the
-  /// LoopVectorizationLegality to handle inductions and reductions, which is
-  /// why it is kept separate from the VPlan-only cost infrastructure.
-  ///
-  /// TODO: Move to VPlan::cost once the use of LoopVectorizationLegality has
-  /// been retired.
-  InstructionCost cost(VPlan &Plan, ElementCount VF) const;
-
 public:
   LoopVectorizationPlanner(
       Loop *L, LoopInfo *LI, DominatorTree *DT, const TargetLibraryInfo *TLI,
@@ -375,9 +365,6 @@ class LoopVectorizationPlanner {
   /// Return the best VPlan for \p VF.
   VPlan &getBestPlanFor(ElementCount VF) const;
 
-  /// Return the most profitable plan and fix its VF to the most profitable one.
-  VPlan &getBestPlan() const;
-
   /// Generate the IR code for the vectorized loop captured in VPlan \p BestPlan
   /// according to the best selected \p VF and  \p UF.
   ///
@@ -456,9 +443,7 @@ class LoopVectorizationPlanner {
                                   ElementCount MinVF);
 
   /// \return The most profitable vectorization factor and the cost of that VF.
-  /// This method checks every VF in \p CandidateVFs. This is now only used to
-  /// verify the decisions by the new VPlan-based cost-model and will be retired
-  /// once the VPlan-based cost-model is stabilized.
+  /// This method checks every VF in \p CandidateVFs.
   VectorizationFactor
   selectVectorizationFactor(const ElementCountSet &CandidateVFs);
 

llvm/lib/Transforms/Vectorize/LoopVectorize.cpp

@@ -290,7 +290,7 @@ static cl::opt<unsigned> ForceTargetMaxVectorInterleaveFactor(
     cl::desc("A flag that overrides the target's max interleave factor for "
              "vectorized loops."));
 
-cl::opt<unsigned> ForceTargetInstructionCost(
+static cl::opt<unsigned> ForceTargetInstructionCost(
     "force-target-instruction-cost", cl::init(0), cl::Hidden,
     cl::desc("A flag that overrides the target's expected cost for "
              "an instruction to a single constant value. Mostly "
@@ -412,6 +412,14 @@ static bool hasIrregularType(Type *Ty, const DataLayout &DL) {
   return DL.getTypeAllocSizeInBits(Ty) != DL.getTypeSizeInBits(Ty);
 }
 
+/// A helper function that returns the reciprocal of the block probability of
+/// predicated blocks. If we return X, we are assuming the predicated block
+/// will execute once for every X iterations of the loop header.
+///
+/// TODO: We should use actual block probability here, if available. Currently,
+///       we always assume predicated blocks have a 50% chance of executing.
+static unsigned getReciprocalPredBlockProb() { return 2; }
+
 /// Returns "best known" trip count for the specified loop \p L as defined by
 /// the following procedure:
 ///   1) Returns exact trip count if it is known.
@@ -1613,16 +1621,6 @@ class LoopVectorizationCostModel {
   /// \p VF is the vectorization factor chosen for the original loop.
   bool isEpilogueVectorizationProfitable(const ElementCount VF) const;
 
-  /// Return the cost of instructions in an inloop reduction pattern, if I is
-  /// part of that pattern.
-  std::optional<InstructionCost>
-  getReductionPatternCost(Instruction *I, ElementCount VF, Type *VectorTy,
-                          TTI::TargetCostKind CostKind) const;
-
-  /// Returns the execution time cost of an instruction for a given vector
-  /// width. Vector width of one means scalar.
-  VectorizationCostTy getInstructionCost(Instruction *I, ElementCount VF);
-
 private:
   unsigned NumPredStores = 0;
 
@@ -1648,11 +1646,21 @@ class LoopVectorizationCostModel {
   /// of elements.
   ElementCount getMaxLegalScalableVF(unsigned MaxSafeElements);
 
+  /// Returns the execution time cost of an instruction for a given vector
+  /// width. Vector width of one means scalar.
+  VectorizationCostTy getInstructionCost(Instruction *I, ElementCount VF);
+
   /// The cost-computation logic from getInstructionCost which provides
   /// the vector type as an output parameter.
   InstructionCost getInstructionCost(Instruction *I, ElementCount VF,
                                      Type *&VectorTy);
 
+  /// Return the cost of instructions in an inloop reduction pattern, if I is
+  /// part of that pattern.
+  std::optional<InstructionCost>
+  getReductionPatternCost(Instruction *I, ElementCount VF, Type *VectorTy,
+                          TTI::TargetCostKind CostKind) const;
+
   /// Calculate vectorization cost of memory instruction \p I.
   InstructionCost getMemoryInstructionCost(Instruction *I, ElementCount VF);
 
@@ -7289,10 +7297,7 @@ LoopVectorizationPlanner::plan(ElementCount UserVF, unsigned UserIC) {
   if (!MaxFactors.hasVector())
     return VectorizationFactor::Disabled();
 
-  // Select the optimal vectorization factor according to the legacy cost-model.
-  // This is now only used to verify the decisions by the new VPlan-based
-  // cost-model and will be retired once the VPlan-based cost-model is
-  // stabilized.
+  // Select the optimal vectorization factor.
   VectorizationFactor VF = selectVectorizationFactor(VFCandidates);
   assert((VF.Width.isScalar() || VF.ScalarCost > 0) && "when vectorizing, the scalar cost must be non-zero.");
   if (!hasPlanWithVF(VF.Width)) {
@@ -7303,189 +7308,6 @@ LoopVectorizationPlanner::plan(ElementCount UserVF, unsigned UserIC) {
   return VF;
 }
 
-InstructionCost VPCostContext::getLegacyCost(Instruction *UI,
-                                             ElementCount VF) const {
-  return CM.getInstructionCost(UI, VF).first;
-}
-
-bool VPCostContext::skipCostComputation(Instruction *UI, bool IsVector) const {
-  return (IsVector && CM.VecValuesToIgnore.contains(UI)) ||
-         SkipCostComputation.contains(UI);
-}
-
-InstructionCost LoopVectorizationPlanner::cost(VPlan &Plan,
-                                               ElementCount VF) const {
-  InstructionCost Cost = 0;
-  LLVMContext &LLVMCtx = OrigLoop->getHeader()->getContext();
-  VPCostContext CostCtx(CM.TTI, Legal->getWidestInductionType(), LLVMCtx, CM);
-
-  // Cost modeling for inductions is inaccurate in the legacy cost model
-  // compared to the recipes that are generated. To match here initially during
-  // VPlan cost model bring up directly use the induction costs from the legacy
-  // cost model. Note that we do this as pre-processing; the VPlan may not have
-  // any recipes associated with the original induction increment instruction
-  // and may replace truncates with VPWidenIntOrFpInductionRecipe. We precompute
-  // the cost of induction phis and increments (both that are represented by
-  // recipes and those that are not), to avoid distinguishing between them here,
-  // and skip all recipes that represent induction phis and increments (the
-  // former case) later on, if they exist, to avoid counting them twice.
-  // Similarly we pre-compute the cost of any optimized truncates.
-  // TODO: Switch to more accurate costing based on VPlan.
-  for (const auto &[IV, IndDesc] : Legal->getInductionVars()) {
-    Instruction *IVInc = cast<Instruction>(
-        IV->getIncomingValueForBlock(OrigLoop->getLoopLatch()));
-    SmallVector<Instruction *> IVInsts = {IV, IVInc};
-    for (User *U : IV->users()) {
-      auto *CI = cast<Instruction>(U);
-      if (!CostCtx.CM.isOptimizableIVTruncate(CI, VF))
-        continue;
-      IVInsts.push_back(CI);
-    }
-    for (Instruction *IVInst : IVInsts) {
-      if (!CostCtx.SkipCostComputation.insert(IVInst).second)
-        continue;
-      InstructionCost InductionCost = CostCtx.getLegacyCost(IVInst, VF);
-      LLVM_DEBUG({
-        dbgs() << "Cost of " << InductionCost << " for VF " << VF
-               << ": induction instruction " << *IVInst << "\n";
-      });
-      Cost += InductionCost;
-    }
-  }
-
-  /// Compute the cost of all exiting conditions of the loop using the legacy
-  /// cost model. This is to match the legacy behavior, which adds the cost of
-  /// all exit conditions. Note that this over-estimates the cost, as there will
-  /// be a single condition to control the vector loop.
-  SmallVector<BasicBlock *> Exiting;
-  CM.TheLoop->getExitingBlocks(Exiting);
-  SetVector<Instruction *> ExitInstrs;
-  // Collect all exit conditions.
-  for (BasicBlock *EB : Exiting) {
-    auto *Term = dyn_cast<BranchInst>(EB->getTerminator());
-    if (!Term)
-      continue;
-    if (auto *CondI = dyn_cast<Instruction>(Term->getOperand(0))) {
-      ExitInstrs.insert(CondI);
-    }
-  }
-  // Compute the cost of all instructions only feeding the exit conditions.
-  for (unsigned I = 0; I != ExitInstrs.size(); ++I) {
-    Instruction *CondI = ExitInstrs[I];
-    if (!OrigLoop->contains(CondI) ||
-        !CostCtx.SkipCostComputation.insert(CondI).second)
-      continue;
-    Cost += CostCtx.getLegacyCost(CondI, VF);
-    for (Value *Op : CondI->operands()) {
-      auto *OpI = dyn_cast<Instruction>(Op);
-      if (!OpI || any_of(OpI->users(), [&ExitInstrs](User *U) {
-            return !ExitInstrs.contains(cast<Instruction>(U));
-          }))
-        continue;
-      ExitInstrs.insert(OpI);
-    }
-  }
-
-  // The legacy cost model has special logic to compute the cost of in-loop
-  // reductions, which may be smaller than the sum of all instructions involved
-  // in the reduction. For AnyOf reductions, VPlan codegen may remove the select
-  // which the legacy cost model uses to assign cost. Pre-compute their costs
-  // for now.
-  // TODO: Switch to costing based on VPlan once the logic has been ported.
-  for (const auto &[RedPhi, RdxDesc] : Legal->getReductionVars()) {
-    if (!CM.isInLoopReduction(RedPhi) &&
-        !RecurrenceDescriptor::isAnyOfRecurrenceKind(
-            RdxDesc.getRecurrenceKind()))
-      continue;
-
-    // AnyOf reduction codegen may remove the select. To match the legacy cost
-    // model, pre-compute the cost for AnyOf reductions here.
-    if (RecurrenceDescriptor::isAnyOfRecurrenceKind(
-            RdxDesc.getRecurrenceKind())) {
-      auto *Select = cast<SelectInst>(*find_if(
-          RedPhi->users(), [](User *U) { return isa<SelectInst>(U); }));
-      assert(!CostCtx.SkipCostComputation.contains(Select) &&
-             "reduction op visited multiple times");
-      CostCtx.SkipCostComputation.insert(Select);
-      auto ReductionCost = CostCtx.getLegacyCost(Select, VF);
-      LLVM_DEBUG(dbgs() << "Cost of " << ReductionCost << " for VF " << VF
-                        << ":\n any-of reduction " << *Select << "\n");
-      Cost += ReductionCost;
-      continue;
-    }
-
-    const auto &ChainOps = RdxDesc.getReductionOpChain(RedPhi, OrigLoop);
-    SetVector<Instruction *> ChainOpsAndOperands(ChainOps.begin(),
-                                                 ChainOps.end());
-    // Also include the operands of instructions in the chain, as the cost-model
-    // may mark extends as free.
-    for (auto *ChainOp : ChainOps) {
-      for (Value *Op : ChainOp->operands()) {
-        if (auto *I = dyn_cast<Instruction>(Op))
-          ChainOpsAndOperands.insert(I);
-      }
-    }
-
-    // Pre-compute the cost for I, if it has a reduction pattern cost.
-    for (Instruction *I : ChainOpsAndOperands) {
-      auto ReductionCost = CM.getReductionPatternCost(
-          I, VF, ToVectorTy(I->getType(), VF), TTI::TCK_RecipThroughput);
-      if (!ReductionCost)
-        continue;
-
-      assert(!CostCtx.SkipCostComputation.contains(I) &&
-             "reduction op visited multiple times");
-      CostCtx.SkipCostComputation.insert(I);
-      LLVM_DEBUG(dbgs() << "Cost of " << ReductionCost << " for VF " << VF
-                        << ":\n in-loop reduction " << *I << "\n");
-      Cost += *ReductionCost;
-    }
-  }
-
-  // Now compute and add the VPlan-based cost.
-  Cost += Plan.cost(VF, CostCtx);
-  LLVM_DEBUG(dbgs() << "Cost for VF " << VF << ": " << Cost << "\n");
-  return Cost;
-}
-
-VPlan &LoopVectorizationPlanner::getBestPlan() const {
-  // If there is a single VPlan with a single VF, return it directly.
-  VPlan &FirstPlan = *VPlans[0];
-  if (VPlans.size() == 1 && size(FirstPlan.vectorFactors()) == 1)
-    return FirstPlan;
-
-  VPlan *BestPlan = &FirstPlan;
-  ElementCount ScalarVF = ElementCount::getFixed(1);
-  assert(hasPlanWithVF(ScalarVF) &&
-         "More than a single plan/VF w/o any plan having scalar VF");
-
-  InstructionCost ScalarCost = cost(getBestPlanFor(ScalarVF), ScalarVF);
-  VectorizationFactor BestFactor(ScalarVF, ScalarCost, ScalarCost);
-
-  bool ForceVectorization = Hints.getForce() == LoopVectorizeHints::FK_Enabled;
-  if (ForceVectorization) {
-    // Ignore scalar width, because the user explicitly wants vectorization.
-    // Initialize cost to max so that VF = 2 is, at least, chosen during cost
-    // evaluation.
-    BestFactor.Cost = InstructionCost::getMax();
-  }
-
-  for (auto &P : VPlans) {
-    for (ElementCount VF : P->vectorFactors()) {
-      if (VF.isScalar())
-        continue;
-      InstructionCost Cost = cost(*P, VF);
-      VectorizationFactor CurrentFactor(VF, Cost, ScalarCost);
-      if (isMoreProfitable(CurrentFactor, BestFactor)) {
-        BestFactor = CurrentFactor;
-        BestPlan = &*P;
-      }
-    }
-  }
-  BestPlan->setVF(BestFactor.Width);
-  return *BestPlan;
-}
-
 VPlan &LoopVectorizationPlanner::getBestPlanFor(ElementCount VF) const {
   assert(count_if(VPlans,
                   [VF](const VPlanPtr &Plan) { return Plan->hasVF(VF); }) ==
@@ -10344,15 +10166,8 @@ bool LoopVectorizePass::processLoop(Loop *L) {
                                VF.MinProfitableTripCount, IC, &LVL, &CM, BFI,
                                PSI, Checks);
 
-        VPlan &BestPlan = LVP.getBestPlan();
-        assert(size(BestPlan.vectorFactors()) == 1 &&
-               "Plan should have a single VF");
-        ElementCount Width = *BestPlan.vectorFactors().begin();
-        LLVM_DEBUG(dbgs() << "VF picked by VPlan cost model: " << Width
-                          << "\n");
-        assert(VF.Width == Width &&
-               "VPlan cost model and legacy cost model disagreed");
-        LVP.executePlan(Width, IC, BestPlan, LB, DT, false);
+        VPlan &BestPlan = LVP.getBestPlanFor(VF.Width);
+        LVP.executePlan(VF.Width, IC, BestPlan, LB, DT, false);
         ++LoopsVectorized;
 
         // Add metadata to disable runtime unrolling a scalar loop when there