VPRecipeBuilder.h

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//===- VPRecipeBuilder.h - Helper class to build recipes --------*- C++ -*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
 
#ifndef LLVM_TRANSFORMS_VECTORIZE_VPRECIPEBUILDER_H
#define LLVM_TRANSFORMS_VECTORIZE_VPRECIPEBUILDER_H
 
#include "LoopVectorizationPlanner.h"
#include "VPlan.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/Analysis/ScalarEvolutionExpressions.h"
 
namespace llvm {
 
class LoopVectorizationLegality;
class LoopVectorizationCostModel;
class TargetLibraryInfo;
class TargetTransformInfo;
struct HistogramInfo;
struct VFRange;
 
/// A chain of instructions that form a partial reduction.
/// Designed to match either:
///   reduction_bin_op (extend (A), accumulator), or
///   reduction_bin_op (bin_op (extend (A), (extend (B))), accumulator).
struct PartialReductionChain {
  PartialReductionChain(Instruction *Reduction, Instruction *ExtendA,
                        Instruction *ExtendB, Instruction *ExtendUser)
      : Reduction(Reduction), ExtendA(ExtendA), ExtendB(ExtendB),
        ExtendUser(ExtendUser) {}
  /// The top-level binary operation that forms the reduction to a scalar
  /// after the loop body.
  Instruction *Reduction;
  /// The extension of each of the inner binary operation's operands.
  Instruction *ExtendA;
  Instruction *ExtendB;
 
  /// The user of the extends that is then reduced.
  Instruction *ExtendUser;
};
 
/// Helper class to create VPRecipies from IR instructions.
class VPRecipeBuilder {
  /// The VPlan new recipes are added to.
  VPlan &Plan;
 
  /// The loop that we evaluate.
  Loop *OrigLoop;
 
  /// Target Library Info.
  const TargetLibraryInfo *TLI;
 
  // Target Transform Info.
  const TargetTransformInfo *TTI;
 
  /// The legality analysis.
  LoopVectorizationLegality *Legal;
 
  /// The profitablity analysis.
  LoopVectorizationCostModel &CM;
 
  PredicatedScalarEvolution &PSE;
 
  VPBuilder &Builder;
 
  /// The mask of each VPBB, generated earlier and used for predicating recipes
  /// in VPBB.
  /// TODO: remove by applying predication when generating the masks.
  DenseMap<VPBasicBlock *, VPValue *> &BlockMaskCache;
 
  // VPlan construction support: Hold a mapping from ingredients to
  // their recipe.
  DenseMap<Instruction *, VPRecipeBase *> Ingredient2Recipe;
 
  /// Cross-iteration reduction & first-order recurrence phis for which we need
  /// to add the incoming value from the backedge after all recipes have been
  /// created.
  SmallVector<VPHeaderPHIRecipe *, 4> PhisToFix;
 
  /// A mapping of partial reduction exit instructions to their scaling factor.
  DenseMap<const Instruction *, unsigned> ScaledReductionMap;
 
  /// Check if \p I can be widened at the start of \p Range and possibly
  /// decrease the range such that the returned value holds for the entire \p
  /// Range. The function should not be called for memory instructions or calls.
  bool shouldWiden(Instruction *I, VFRange &Range) const;
 
  /// Check if the load or store instruction \p VPI should widened for \p
  /// Range.Start and potentially masked. Such instructions are handled by a
  /// recipe that takes an additional VPInstruction for the mask.
  VPWidenMemoryRecipe *tryToWidenMemory(VPInstruction *VPI, VFRange &Range);
 
  /// Check if an induction recipe should be constructed for \p VPI. If so build
  /// and return it. If not, return null.
  VPHeaderPHIRecipe *tryToOptimizeInductionPHI(VPInstruction *VPI);
 
  /// Optimize the special case where the operand of \p VPI is a constant
  /// integer induction variable.
  VPWidenIntOrFpInductionRecipe *
  tryToOptimizeInductionTruncate(VPInstruction *VPI, VFRange &Range);
 
  /// Handle call instructions. If \p VPI can be widened for \p Range.Start,
  /// return a new VPWidenCallRecipe or VPWidenIntrinsicRecipe. Range.End may be
  /// decreased to ensure same decision from \p Range.Start to \p Range.End.
  VPSingleDefRecipe *tryToWidenCall(VPInstruction *VPI, VFRange &Range);
 
  /// Check if \p VPI has an opcode that can be widened and return a
  /// VPWidenRecipe if it can. The function should only be called if the
  /// cost-model indicates that widening should be performed.
  VPWidenRecipe *tryToWiden(VPInstruction *VPI);
 
  /// Makes Histogram count operations safe for vectorization, by emitting a
  /// llvm.experimental.vector.histogram.add intrinsic in place of the
  /// Load + Add|Sub + Store operations that perform the histogram in the
  /// original scalar loop.
  VPHistogramRecipe *tryToWidenHistogram(const HistogramInfo *HI,
                                         VPInstruction *VPI);
 
  /// Examines reduction operations to see if the target can use a cheaper
  /// operation with a wider per-iteration input VF and narrower PHI VF.
  /// Each element within Chains is a pair with a struct containing reduction
  /// information and the scaling factor between the number of elements in
  /// the input and output.
  /// Recursively calls itself to identify chained scaled reductions.
  /// Returns true if this invocation added an entry to Chains, otherwise false.
  /// i.e. returns false in the case that a subcall adds an entry to Chains,
  /// but the top-level call does not.
  bool getScaledReductions(
      Instruction *PHI, Instruction *RdxExitInstr, VFRange &Range,
      SmallVectorImpl<std::pair<PartialReductionChain, unsigned>> &Chains);
 
public:
  VPRecipeBuilder(VPlan &Plan, Loop *OrigLoop, const TargetLibraryInfo *TLI,
                  const TargetTransformInfo *TTI,
                  LoopVectorizationLegality *Legal,
                  LoopVectorizationCostModel &CM,
                  PredicatedScalarEvolution &PSE, VPBuilder &Builder,
                  DenseMap<VPBasicBlock *, VPValue *> &BlockMaskCache)
      : Plan(Plan), OrigLoop(OrigLoop), TLI(TLI), TTI(TTI), Legal(Legal),
        CM(CM), PSE(PSE), Builder(Builder), BlockMaskCache(BlockMaskCache) {}
 
  std::optional<unsigned> getScalingForReduction(const Instruction *ExitInst) {
    auto It = ScaledReductionMap.find(ExitInst);
    return It == ScaledReductionMap.end() ? std::nullopt
                                          : std::make_optional(It->second);
  }
 
  /// Find all possible partial reductions in the loop and track all of those
  /// that are valid so recipes can be formed later.
  void collectScaledReductions(VFRange &Range);
 
  /// Create and return a widened recipe for \p R if one can be created within
  /// the given VF \p Range.
  VPRecipeBase *tryToCreateWidenRecipe(VPSingleDefRecipe *R, VFRange &Range);
 
  /// Create and return a partial reduction recipe for a reduction instruction
  /// along with binary operation and reduction phi operands.
  VPRecipeBase *tryToCreatePartialReduction(VPInstruction *Reduction,
                                            unsigned ScaleFactor);
 
  /// Set the recipe created for given ingredient.
  void setRecipe(Instruction *I, VPRecipeBase *R) {
    assert(!Ingredient2Recipe.contains(I) &&
           "Cannot reset recipe for instruction.");
    Ingredient2Recipe[I] = R;
  }
 
  /// Returns the *entry* mask for block \p VPBB or null if the mask is
  /// all-true.
  VPValue *getBlockInMask(VPBasicBlock *VPBB) const {
    return BlockMaskCache.lookup(VPBB);
  }
 
  /// Return the recipe created for given ingredient.
  VPRecipeBase *getRecipe(Instruction *I) {
    assert(Ingredient2Recipe.count(I) &&
           "Recording this ingredients recipe was not requested");
    assert(Ingredient2Recipe[I] != nullptr &&
           "Ingredient doesn't have a recipe");
    return Ingredient2Recipe[I];
  }
 
  /// Build a VPReplicationRecipe for \p VPI. If it is predicated, add the mask
  /// as last operand. Range.End may be decreased to ensure same recipe behavior
  /// from \p Range.Start to \p Range.End.
  VPReplicateRecipe *handleReplication(VPInstruction *VPI, VFRange &Range);
 
  VPValue *getVPValueOrAddLiveIn(Value *V) {
    if (auto *I = dyn_cast<Instruction>(V)) {
      if (auto *R = Ingredient2Recipe.lookup(I))
        return R->getVPSingleValue();
    }
    return Plan.getOrAddLiveIn(V);
  }
 
  void updateBlockMaskCache(DenseMap<VPValue *, VPValue *> &Old2New) {
    for (auto &[_, V] : BlockMaskCache) {
      if (auto *New = Old2New.lookup(V)) {
        V->replaceAllUsesWith(New);
        V = New;
      }
    }
  }
};
} // end namespace llvm
 
#endif // LLVM_TRANSFORMS_VECTORIZE_VPRECIPEBUILDER_H