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//===- llvm/Analysis/LegacyDivergenceAnalysis.h - KernelDivergence Analysis -*- 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

//

//===----------------------------------------------------------------------===//

//

// The kernel divergence analysis is an LLVM pass which can be used to find out

// if a branch instruction in a GPU program (kernel) is divergent or not. It can help

// branch optimizations such as jump threading and loop unswitching to make

// better decisions.

//

//===----------------------------------------------------------------------===//

#ifndef LLVM_ANALYSIS_LEGACYDIVERGENCEANALYSIS_H

#define LLVM_ANALYSIS_LEGACYDIVERGENCEANALYSIS_H

#include "llvm/ADT/DenseSet.h"

#include "llvm/Analysis/LoopInfo.h"

#include "llvm/Analysis/PostDominators.h"

#include "llvm/IR/PassManager.h"

#include "llvm/Pass.h"

#include <memory>

namespace llvm {

class DivergenceInfo;

class Function;

class Module;

class raw_ostream;

class TargetTransformInfo;

class Use;

class Value;

class LegacyDivergenceAnalysisImpl {

public:

  // Returns true if V is divergent at its definition.

  bool isDivergent(const Value *V) const;

  // Returns true if U is divergent. Uses of a uniform value can be divergent.

  bool isDivergentUse(const Use *U) const;

  // Returns true if V is uniform/non-divergent.

  bool isUniform(const Value *V) const { return !isDivergent(V); }

  // Returns true if U is uniform/non-divergent. Uses of a uniform value can be

  // divergent.

  bool isUniformUse(const Use *U) const { return !isDivergentUse(U); }

  // Keep the analysis results uptodate by removing an erased value.

  void removeValue(const Value *V) { DivergentValues.erase(V); }

  // Print all divergent branches in the function.

  void print(raw_ostream &OS, const Module *) const;

  // Whether analysis should be performed by GPUDivergenceAnalysis.

  bool shouldUseGPUDivergenceAnalysis(const Function &F,

                                      const TargetTransformInfo &TTI,

                                      const LoopInfo &LI);

  void run(Function &F, TargetTransformInfo &TTI, DominatorTree &DT,

           PostDominatorTree &PDT, const LoopInfo &LI);

protected:

  // (optional) handle to new DivergenceAnalysis

  std::unique_ptr<DivergenceInfo> gpuDA;

  // Stores all divergent values.

  DenseSet<const Value *> DivergentValues;

  // Stores divergent uses of possibly uniform values.

  DenseSet<const Use *> DivergentUses;

};

class LegacyDivergenceAnalysis : public FunctionPass,

                                 public LegacyDivergenceAnalysisImpl {

public:

  static char ID;

  LegacyDivergenceAnalysis();

  void getAnalysisUsage(AnalysisUsage &AU) const override;

  bool runOnFunction(Function &F) override;

};

class LegacyDivergenceAnalysisPass

    : public PassInfoMixin<LegacyDivergenceAnalysisPass>,

      public LegacyDivergenceAnalysisImpl {

public:

  PreservedAnalyses run(Function &F, FunctionAnalysisManager &AM);

private:

  // (optional) handle to new DivergenceAnalysis

  std::unique_ptr<DivergenceInfo> gpuDA;

  // Stores all divergent values.

  DenseSet<const Value *> DivergentValues;

  // Stores divergent uses of possibly uniform values.

  DenseSet<const Use *> DivergentUses;

};

} // end namespace llvm

#endif // LLVM_ANALYSIS_LEGACYDIVERGENCEANALYSIS_H