1 //===- llvm/Analysis/LegacyDivergenceAnalysis.h - KernelDivergence Analysis -*- C++ -*-===// 2 // 3 // The LLVM Compiler Infrastructure 4 // 5 // This file is distributed under the University of Illinois Open Source 6 // License. See LICENSE.TXT for details. 7 // 8 //===----------------------------------------------------------------------===// 9 // 10 // The kernel divergence analysis is an LLVM pass which can be used to find out 11 // if a branch instruction in a GPU program (kernel) is divergent or not. It can help 12 // branch optimizations such as jump threading and loop unswitching to make 13 // better decisions. 14 // 15 //===----------------------------------------------------------------------===// 16 #ifndef LLVM_ANALYSIS_LEGACY_DIVERGENCE_ANALYSIS_H 17 #define LLVM_ANALYSIS_LEGACY_DIVERGENCE_ANALYSIS_H 18 19 #include "llvm/ADT/DenseSet.h" 20 #include "llvm/IR/Function.h" 21 #include "llvm/Pass.h" 22 #include "llvm/Analysis/DivergenceAnalysis.h" 23 24 namespace llvm { 25 class Value; 26 class GPUDivergenceAnalysis; 27 class LegacyDivergenceAnalysis : public FunctionPass { 28 public: 29 static char ID; 30 LegacyDivergenceAnalysis()31 LegacyDivergenceAnalysis() : FunctionPass(ID) { 32 initializeLegacyDivergenceAnalysisPass(*PassRegistry::getPassRegistry()); 33 } 34 35 void getAnalysisUsage(AnalysisUsage &AU) const override; 36 37 bool runOnFunction(Function &F) override; 38 39 // Print all divergent branches in the function. 40 void print(raw_ostream &OS, const Module *) const override; 41 42 // Returns true if V is divergent at its definition. 43 // 44 // Even if this function returns false, V may still be divergent when used 45 // in a different basic block. 46 bool isDivergent(const Value *V) const; 47 48 // Returns true if V is uniform/non-divergent. 49 // 50 // Even if this function returns true, V may still be divergent when used 51 // in a different basic block. isUniform(const Value * V)52 bool isUniform(const Value *V) const { return !isDivergent(V); } 53 54 // Keep the analysis results uptodate by removing an erased value. removeValue(const Value * V)55 void removeValue(const Value *V) { DivergentValues.erase(V); } 56 57 private: 58 // Whether analysis should be performed by GPUDivergenceAnalysis. 59 bool shouldUseGPUDivergenceAnalysis(const Function &F) const; 60 61 // (optional) handle to new DivergenceAnalysis 62 std::unique_ptr<GPUDivergenceAnalysis> gpuDA; 63 64 // Stores all divergent values. 65 DenseSet<const Value *> DivergentValues; 66 }; 67 } // End llvm namespace 68 69 #endif //LLVM_ANALYSIS_LEGACY_DIVERGENCE_ANALYSIS_H 70