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_LEGACY_DIVERGENCE_ANALYSIS_H 16 #define LLVM_ANALYSIS_LEGACY_DIVERGENCE_ANALYSIS_H 17 18 #include "llvm/ADT/DenseSet.h" 19 #include "llvm/Analysis/DivergenceAnalysis.h" 20 #include "llvm/Pass.h" 21 22 namespace llvm { 23 class Value; 24 class Function; 25 class GPUDivergenceAnalysis; 26 class LegacyDivergenceAnalysis : public FunctionPass { 27 public: 28 static char ID; 29 30 LegacyDivergenceAnalysis(); 31 32 void getAnalysisUsage(AnalysisUsage &AU) const override; 33 34 bool runOnFunction(Function &F) override; 35 36 // Print all divergent branches in the function. 37 void print(raw_ostream &OS, const Module *) const override; 38 39 // Returns true if V is divergent at its definition. 40 bool isDivergent(const Value *V) const; 41 42 // Returns true if U is divergent. Uses of a uniform value can be divergent. 43 bool isDivergentUse(const Use *U) const; 44 45 // Returns true if V is uniform/non-divergent. isUniform(const Value * V)46 bool isUniform(const Value *V) const { return !isDivergent(V); } 47 48 // Returns true if U is uniform/non-divergent. Uses of a uniform value can be 49 // divergent. isUniformUse(const Use * U)50 bool isUniformUse(const Use *U) const { return !isDivergentUse(U); } 51 52 // Keep the analysis results uptodate by removing an erased value. removeValue(const Value * V)53 void removeValue(const Value *V) { DivergentValues.erase(V); } 54 55 private: 56 // Whether analysis should be performed by GPUDivergenceAnalysis. 57 bool shouldUseGPUDivergenceAnalysis(const Function &F) const; 58 59 // (optional) handle to new DivergenceAnalysis 60 std::unique_ptr<GPUDivergenceAnalysis> gpuDA; 61 62 // Stores all divergent values. 63 DenseSet<const Value *> DivergentValues; 64 65 // Stores divergent uses of possibly uniform values. 66 DenseSet<const Use *> DivergentUses; 67 }; 68 } // End llvm namespace 69 70 #endif //LLVM_ANALYSIS_LEGACY_DIVERGENCE_ANALYSIS_H 71