1 //===- PhiValues.h - Phi Value 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 // This file defines the PhiValues class, and associated passes, which can be
10 // used to find the underlying values of the phis in a function, i.e. the
11 // non-phi values that can be found by traversing the phi graph.
12 //
13 // This information is computed lazily and cached. If new phis are added to the
14 // function they are handled correctly, but if an existing phi has its operands
15 // modified PhiValues has to be notified by calling invalidateValue.
16 //
17 //===----------------------------------------------------------------------===//
18 
19 #ifndef LLVM_ANALYSIS_PHIVALUES_H
20 #define LLVM_ANALYSIS_PHIVALUES_H
21 
22 #include "llvm/ADT/DenseMap.h"
23 #include "llvm/ADT/DenseSet.h"
24 #include "llvm/ADT/SetVector.h"
25 #include "llvm/IR/PassManager.h"
26 #include "llvm/IR/ValueHandle.h"
27 #include "llvm/Pass.h"
28 
29 namespace llvm {
30 
31 class Value;
32 class PHINode;
33 class Function;
34 
35 /// Class for calculating and caching the underlying values of phis in a
36 /// function.
37 ///
38 /// Initially the PhiValues is empty, and gets incrementally populated whenever
39 /// it is queried.
40 class PhiValues {
41 public:
42   using ValueSet = SmallSetVector<Value *, 4>;
43 
44   /// Construct an empty PhiValues.
PhiValues(const Function & F)45   PhiValues(const Function &F) : F(F) {}
46 
47   /// Get the underlying values of a phi.
48   ///
49   /// This returns the cached value if PN has previously been processed,
50   /// otherwise it processes it first.
51   const ValueSet &getValuesForPhi(const PHINode *PN);
52 
53   /// Notify PhiValues that the cached information using V is no longer valid
54   ///
55   /// Whenever a phi has its operands modified the cached values for that phi
56   /// (and the phis that use that phi) become invalid. A user of PhiValues has
57   /// to notify it of this by calling invalidateValue on either the operand or
58   /// the phi, which will then clear the relevant cached information.
59   void invalidateValue(const Value *V);
60 
61   /// Free the memory used by this class.
62   void releaseMemory();
63 
64   /// Print out the values currently in the cache.
65   void print(raw_ostream &OS) const;
66 
67   /// Handle invalidation events in the new pass manager.
68   bool invalidate(Function &, const PreservedAnalyses &,
69                   FunctionAnalysisManager::Invalidator &);
70 
71 private:
72   using ConstValueSet = SmallSetVector<const Value *, 4>;
73 
74   /// The next depth number to be used by processPhi.
75   unsigned int NextDepthNumber = 1;
76 
77   /// Depth numbers of phis. Phis with the same depth number are part of the
78   /// same strongly connected component.
79   DenseMap<const PHINode *, unsigned int> DepthMap;
80 
81   /// Non-phi values reachable from each component.
82   DenseMap<unsigned int, ValueSet> NonPhiReachableMap;
83 
84   /// All values reachable from each component.
85   DenseMap<unsigned int, ConstValueSet> ReachableMap;
86 
87   /// A CallbackVH to notify PhiValues when a value is deleted or replaced, so
88   /// that the cached information for that value can be cleared to avoid
89   /// dangling pointers to invalid values.
90   class PhiValuesCallbackVH final : public CallbackVH {
91     PhiValues *PV;
92     void deleted() override;
93     void allUsesReplacedWith(Value *New) override;
94 
95   public:
96     PhiValuesCallbackVH(Value *V, PhiValues *PV = nullptr)
CallbackVH(V)97         : CallbackVH(V), PV(PV) {}
98   };
99 
100   /// A set of callbacks to the values that processPhi has seen.
101   DenseSet<PhiValuesCallbackVH, DenseMapInfo<Value *>> TrackedValues;
102 
103   /// The function that the PhiValues is for.
104   const Function &F;
105 
106   /// Process a phi so that its entries in the depth and reachable maps are
107   /// fully populated.
108   void processPhi(const PHINode *PN, SmallVectorImpl<const PHINode *> &Stack);
109 };
110 
111 /// The analysis pass which yields a PhiValues
112 ///
113 /// The analysis does nothing by itself, and just returns an empty PhiValues
114 /// which will get filled in as it's used.
115 class PhiValuesAnalysis : public AnalysisInfoMixin<PhiValuesAnalysis> {
116   friend AnalysisInfoMixin<PhiValuesAnalysis>;
117   static AnalysisKey Key;
118 
119 public:
120   using Result = PhiValues;
121   PhiValues run(Function &F, FunctionAnalysisManager &);
122 };
123 
124 /// A pass for printing the PhiValues for a function.
125 ///
126 /// This pass doesn't print whatever information the PhiValues happens to hold,
127 /// but instead first uses the PhiValues to analyze all the phis in the function
128 /// so the complete information is printed.
129 class PhiValuesPrinterPass : public PassInfoMixin<PhiValuesPrinterPass> {
130   raw_ostream &OS;
131 
132 public:
PhiValuesPrinterPass(raw_ostream & OS)133   explicit PhiValuesPrinterPass(raw_ostream &OS) : OS(OS) {}
134   PreservedAnalyses run(Function &F, FunctionAnalysisManager &AM);
isRequired()135   static bool isRequired() { return true; }
136 };
137 
138 /// Wrapper pass for the legacy pass manager
139 class PhiValuesWrapperPass : public FunctionPass {
140   std::unique_ptr<PhiValues> Result;
141 
142 public:
143   static char ID;
144   PhiValuesWrapperPass();
145 
getResult()146   PhiValues &getResult() { return *Result; }
getResult()147   const PhiValues &getResult() const { return *Result; }
148 
149   bool runOnFunction(Function &F) override;
150   void releaseMemory() override;
151   void getAnalysisUsage(AnalysisUsage &AU) const override;
152 };
153 
154 } // namespace llvm
155 
156 #endif
157