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_SYNC_DEPENDENCE_ANALYSIS_H 17 #define LLVM_ANALYSIS_SYNC_DEPENDENCE_ANALYSIS_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 25 namespace llvm { 26 27 class BasicBlock; 28 class DominatorTree; 29 class Loop; 30 class PostDominatorTree; 31 32 using ConstBlockSet = SmallPtrSet<const BasicBlock *, 4>; 33 34 /// \brief Relates points of divergent control to join points in 35 /// reducible CFGs. 36 /// 37 /// This analysis relates points of divergent control to points of converging 38 /// divergent control. The analysis requires all loops to be reducible. 39 class SyncDependenceAnalysis { 40 public: 41 ~SyncDependenceAnalysis(); 42 SyncDependenceAnalysis(const DominatorTree &DT, const PostDominatorTree &PDT, 43 const LoopInfo &LI); 44 45 /// \brief Computes divergent join points and loop exits caused by branch 46 /// divergence in \p Term. 47 /// 48 /// The set of blocks which are reachable by disjoint paths from \p Term. 49 /// The set also contains loop exits if there two disjoint paths: 50 /// one from \p Term to the loop exit and another from \p Term to the loop 51 /// header. Those exit blocks are added to the returned set. 52 /// If L is the parent loop of \p Term and an exit of L is in the returned 53 /// set then L is a divergent loop. 54 const ConstBlockSet &join_blocks(const Instruction &Term); 55 56 /// \brief Computes divergent join points and loop exits (in the surrounding 57 /// loop) caused by the divergent loop exits of\p Loop. 58 /// 59 /// The set of blocks which are reachable by disjoint paths from the 60 /// loop exits of \p Loop. 61 /// This treats the loop as a single node in \p Loop's parent loop. 62 /// The returned set has the same properties as for join_blocks(TermInst&). 63 const ConstBlockSet &join_blocks(const Loop &Loop); 64 65 private: 66 static ConstBlockSet EmptyBlockSet; 67 68 ReversePostOrderTraversal<const Function *> FuncRPOT; 69 const DominatorTree &DT; 70 const PostDominatorTree &PDT; 71 const LoopInfo &LI; 72 73 std::map<const Loop *, std::unique_ptr<ConstBlockSet>> CachedLoopExitJoins; 74 std::map<const Instruction *, std::unique_ptr<ConstBlockSet>> 75 CachedBranchJoins; 76 }; 77 78 } // namespace llvm 79 80 #endif // LLVM_ANALYSIS_SYNC_DEPENDENCE_ANALYSIS_H 81