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