UnrollLoop.h

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//===- llvm/Transforms/Utils/UnrollLoop.h - Unrolling utilities -*- 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
//
//===----------------------------------------------------------------------===//
//
// This file defines some loop unrolling utilities. It does not define any
// actual pass or policy, but provides a single function to perform loop
// unrolling.
//
//===----------------------------------------------------------------------===//
 
#ifndef LLVM_TRANSFORMS_UTILS_UNROLLLOOP_H
#define LLVM_TRANSFORMS_UTILS_UNROLLLOOP_H
 
#include "llvm/ADT/DenseMap.h"
#include "llvm/Analysis/CodeMetrics.h"
#include "llvm/Analysis/TargetTransformInfo.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/InstructionCost.h"
 
namespace llvm {
 
class AssumptionCache;
class AAResults;
class BasicBlock;
class BlockFrequencyInfo;
class DependenceInfo;
class DominatorTree;
class Loop;
class LoopInfo;
class MDNode;
class ProfileSummaryInfo;
class OptimizationRemarkEmitter;
class ScalarEvolution;
class StringRef;
class Value;
 
using NewLoopsMap = SmallDenseMap<const Loop *, Loop *, 4>;
 
/// @{
/// Metadata attribute names
const char *const LLVMLoopUnrollFollowupAll = "llvm.loop.unroll.followup_all";
const char *const LLVMLoopUnrollFollowupUnrolled =
    "llvm.loop.unroll.followup_unrolled";
const char *const LLVMLoopUnrollFollowupRemainder =
    "llvm.loop.unroll.followup_remainder";
/// @}
 
LLVM_ABI const Loop *addClonedBlockToLoopInfo(BasicBlock *OriginalBB,
                                              BasicBlock *ClonedBB,
                                              LoopInfo *LI,
                                              NewLoopsMap &NewLoops);
 
/// Represents the result of a \c UnrollLoop invocation.
enum class LoopUnrollResult {
  /// The loop was not modified.
  Unmodified,
 
  /// The loop was partially unrolled -- we still have a loop, but with a
  /// smaller trip count.  We may also have emitted epilogue loop if the loop
  /// had a non-constant trip count.
  PartiallyUnrolled,
 
  /// The loop was fully unrolled into straight-line code.  We no longer have
  /// any back-edges.
  FullyUnrolled
};
 
struct UnrollLoopOptions {
  unsigned Count;
  bool Force;
  bool Runtime;
  bool AllowExpensiveTripCount;
  bool UnrollRemainder;
  bool ForgetAllSCEV;
  const Instruction *Heart = nullptr;
  unsigned SCEVExpansionBudget;
  bool RuntimeUnrollMultiExit = false;
  bool AddAdditionalAccumulators = false;
};
 
LLVM_ABI LoopUnrollResult UnrollLoop(Loop *L, UnrollLoopOptions ULO,
                                     LoopInfo *LI, ScalarEvolution *SE,
                                     DominatorTree *DT, AssumptionCache *AC,
                                     const llvm::TargetTransformInfo *TTI,
                                     OptimizationRemarkEmitter *ORE,
                                     bool PreserveLCSSA,
                                     Loop **RemainderLoop = nullptr,
                                     AAResults *AA = nullptr);
 
LLVM_ABI bool UnrollRuntimeLoopRemainder(
    Loop *L, unsigned Count, bool AllowExpensiveTripCount,
    bool UseEpilogRemainder, bool UnrollRemainder, bool ForgetAllSCEV,
    LoopInfo *LI, ScalarEvolution *SE, DominatorTree *DT, AssumptionCache *AC,
    const TargetTransformInfo *TTI, bool PreserveLCSSA,
    unsigned SCEVExpansionBudget, bool RuntimeUnrollMultiExit,
    Loop **ResultLoop = nullptr,
    std::optional<unsigned> OriginalTripCount = std::nullopt,
    BranchProbability OriginalLoopProb = BranchProbability::getUnknown());
 
LLVM_ABI LoopUnrollResult UnrollAndJamLoop(
    Loop *L, unsigned Count, unsigned TripCount, unsigned TripMultiple,
    bool UnrollRemainder, LoopInfo *LI, ScalarEvolution *SE, DominatorTree *DT,
    AssumptionCache *AC, const TargetTransformInfo *TTI,
    OptimizationRemarkEmitter *ORE, Loop **EpilogueLoop = nullptr);
 
LLVM_ABI bool isSafeToUnrollAndJam(Loop *L, ScalarEvolution &SE,
                                   DominatorTree &DT, DependenceInfo &DI,
                                   LoopInfo &LI);
 
LLVM_ABI void simplifyLoopAfterUnroll(Loop *L, bool SimplifyIVs, LoopInfo *LI,
                                      ScalarEvolution *SE, DominatorTree *DT,
                                      AssumptionCache *AC,
                                      const TargetTransformInfo *TTI,
                                      AAResults *AA = nullptr);
 
LLVM_ABI MDNode *GetUnrollMetadata(MDNode *LoopID, StringRef Name);
 
LLVM_ABI TargetTransformInfo::UnrollingPreferences gatherUnrollingPreferences(
    Loop *L, ScalarEvolution &SE, const TargetTransformInfo &TTI,
    BlockFrequencyInfo *BFI, ProfileSummaryInfo *PSI,
    llvm::OptimizationRemarkEmitter &ORE, int OptLevel,
    std::optional<unsigned> UserThreshold, std::optional<unsigned> UserCount,
    std::optional<bool> UserAllowPartial, std::optional<bool> UserRuntime,
    std::optional<bool> UserUpperBound,
    std::optional<unsigned> UserFullUnrollMaxCount);
 
/// Produce an estimate of the unrolled cost of the specified loop.  This
/// is used to a) produce a cost estimate for partial unrolling and b) to
/// cheaply estimate cost for full unrolling when we don't want to symbolically
/// evaluate all iterations.
class UnrollCostEstimator {
  InstructionCost LoopSize;
  bool NotDuplicatable;
 
public:
  unsigned NumInlineCandidates;
  ConvergenceKind Convergence;
  bool ConvergenceAllowsRuntime;
 
  LLVM_ABI UnrollCostEstimator(const Loop *L, const TargetTransformInfo &TTI,
                               const SmallPtrSetImpl<const Value *> &EphValues,
                               unsigned BEInsns);
 
  /// Whether it is legal to unroll this loop.
  LLVM_ABI bool canUnroll() const;
 
  uint64_t getRolledLoopSize() const { return LoopSize.getValue(); }
 
  /// Returns loop size estimation for unrolled loop, given the unrolling
  /// configuration specified by UP.
  LLVM_ABI uint64_t
  getUnrolledLoopSize(const TargetTransformInfo::UnrollingPreferences &UP,
                      unsigned CountOverwrite = 0) const;
};
 
LLVM_ABI bool computeUnrollCount(
    Loop *L, const TargetTransformInfo &TTI, DominatorTree &DT, LoopInfo *LI,
    AssumptionCache *AC, ScalarEvolution &SE,
    const SmallPtrSetImpl<const Value *> &EphValues,
    OptimizationRemarkEmitter *ORE, unsigned TripCount, unsigned MaxTripCount,
    bool MaxOrZero, unsigned TripMultiple, const UnrollCostEstimator &UCE,
    TargetTransformInfo::UnrollingPreferences &UP,
    TargetTransformInfo::PeelingPreferences &PP, bool &UseUpperBound);
 
LLVM_ABI std::optional<RecurrenceDescriptor>
canParallelizeReductionWhenUnrolling(PHINode &Phi, Loop *L,
                                     ScalarEvolution *SE);
} // end namespace llvm
 
#endif // LLVM_TRANSFORMS_UTILS_UNROLLLOOP_H