1 //===- llvm/Analysis/LegacyDivergenceAnalysis.h - KernelDivergence Analysis -*- C++ -*-===// 2 // 3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. 4 // See https://llvm.org/LICENSE.txt for license information. 5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception 6 // 7 //===----------------------------------------------------------------------===// 8 // 9 // The kernel divergence analysis is an LLVM pass which can be used to find out 10 // if a branch instruction in a GPU program (kernel) is divergent or not. It can help 11 // branch optimizations such as jump threading and loop unswitching to make 12 // better decisions. 13 // 14 //===----------------------------------------------------------------------===// 15 #ifndef LLVM_ANALYSIS_LEGACYDIVERGENCEANALYSIS_H 16 #define LLVM_ANALYSIS_LEGACYDIVERGENCEANALYSIS_H 17 18 #include "llvm/ADT/DenseSet.h" 19 #include "llvm/Pass.h" 20 #include <memory> 21 22 namespace llvm { 23 class DivergenceInfo; 24 class Function; 25 class Module; 26 class raw_ostream; 27 class TargetTransformInfo; 28 class Use; 29 class Value; 30 31 class LegacyDivergenceAnalysis : public FunctionPass { 32 public: 33 static char ID; 34 35 LegacyDivergenceAnalysis(); 36 37 void getAnalysisUsage(AnalysisUsage &AU) const override; 38 39 bool runOnFunction(Function &F) override; 40 41 // Print all divergent branches in the function. 42 void print(raw_ostream &OS, const Module *) const override; 43 44 // Returns true if V is divergent at its definition. 45 bool isDivergent(const Value *V) const; 46 47 // Returns true if U is divergent. Uses of a uniform value can be divergent. 48 bool isDivergentUse(const Use *U) const; 49 50 // Returns true if V is uniform/non-divergent. isUniform(const Value * V)51 bool isUniform(const Value *V) const { return !isDivergent(V); } 52 53 // Returns true if U is uniform/non-divergent. Uses of a uniform value can be 54 // divergent. isUniformUse(const Use * U)55 bool isUniformUse(const Use *U) const { return !isDivergentUse(U); } 56 57 // Keep the analysis results uptodate by removing an erased value. removeValue(const Value * V)58 void removeValue(const Value *V) { DivergentValues.erase(V); } 59 60 private: 61 // Whether analysis should be performed by GPUDivergenceAnalysis. 62 bool shouldUseGPUDivergenceAnalysis(const Function &F, 63 const TargetTransformInfo &TTI) const; 64 65 // (optional) handle to new DivergenceAnalysis 66 std::unique_ptr<DivergenceInfo> gpuDA; 67 68 // Stores all divergent values. 69 DenseSet<const Value *> DivergentValues; 70 71 // Stores divergent uses of possibly uniform values. 72 DenseSet<const Use *> DivergentUses; 73 }; 74 } // End llvm namespace 75 76 #endif // LLVM_ANALYSIS_LEGACYDIVERGENCEANALYSIS_H 77