1//===- SyncDependenceAnalysis.h - Divergent Branch Dependence -*- 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// \file 10// This file defines the SyncDependenceAnalysis class, which computes for 11// every divergent branch the set of phi nodes that the branch will make 12// divergent. 13// 14//===----------------------------------------------------------------------===// 15 16#ifndef LLVM_ANALYSIS_SYNCDEPENDENCEANALYSIS_H 17#define LLVM_ANALYSIS_SYNCDEPENDENCEANALYSIS_H 18 19#include "llvm/ADT/DenseMap.h" 20#include "llvm/ADT/PostOrderIterator.h" 21#include "llvm/ADT/SmallPtrSet.h" 22#include "llvm/Analysis/LoopInfo.h" 23#include <memory> 24#include <unordered_map> 25 26namespace llvm { 27 28class BasicBlock; 29class DominatorTree; 30class Loop; 31class PostDominatorTree; 32 33using ConstBlockSet = SmallPtrSet<const BasicBlock *, 4>; 34struct ControlDivergenceDesc { 35 // Join points of divergent disjoint paths. 36 ConstBlockSet JoinDivBlocks; 37 // Divergent loop exits 38 ConstBlockSet LoopDivBlocks; 39}; 40 41struct ModifiedPO { 42 std::vector<const BasicBlock *> LoopPO; 43 std::unordered_map<const BasicBlock *, unsigned> POIndex; 44 void appendBlock(const BasicBlock &BB) { 45 POIndex[&BB] = LoopPO.size(); 46 LoopPO.push_back(&BB); 47 } 48 unsigned getIndexOf(const BasicBlock &BB) const { 49 return POIndex.find(&BB)->second; 50 } 51 unsigned size() const { return LoopPO.size(); } 52 const BasicBlock *getBlockAt(unsigned Idx) const { return LoopPO[Idx]; } 53}; 54 55/// \brief Relates points of divergent control to join points in 56/// reducible CFGs. 57/// 58/// This analysis relates points of divergent control to points of converging 59/// divergent control. The analysis requires all loops to be reducible. 60class SyncDependenceAnalysis { 61public: 62 ~SyncDependenceAnalysis(); 63 SyncDependenceAnalysis(const DominatorTree &DT, const PostDominatorTree &PDT, 64 const LoopInfo &LI); 65 66 /// \brief Computes divergent join points and loop exits caused by branch 67 /// divergence in \p Term. 68 /// 69 /// The set of blocks which are reachable by disjoint paths from \p Term. 70 /// The set also contains loop exits if there two disjoint paths: 71 /// one from \p Term to the loop exit and another from \p Term to the loop 72 /// header. Those exit blocks are added to the returned set. 73 /// If L is the parent loop of \p Term and an exit of L is in the returned 74 /// set then L is a divergent loop. 75 const ControlDivergenceDesc &getJoinBlocks(const Instruction &Term); 76 77private: 78 static ControlDivergenceDesc EmptyDivergenceDesc; 79 80 ModifiedPO LoopPO; 81 82 const DominatorTree &DT; 83 const PostDominatorTree &PDT; 84 const LoopInfo &LI; 85 86 std::map<const Instruction *, std::unique_ptr<ControlDivergenceDesc>> 87 CachedControlDivDescs; 88}; 89 90} // namespace llvm 91 92#endif // LLVM_ANALYSIS_SYNCDEPENDENCEANALYSIS_H 93