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/SmallPtrSet.h"
25 #include "llvm/ADT/SmallVector.h"
26 #include "llvm/IR/PassManager.h"
27 #include "llvm/IR/ValueHandle.h"
28 #include "llvm/Pass.h"
29 
30 namespace llvm {
31 
32 class Use;
33 class Value;
34 class PHINode;
35 class Function;
36 
37 /// Class for calculating and caching the underlying values of phis in a
38 /// function.
39 ///
40 /// Initially the PhiValues is empty, and gets incrementally populated whenever
41 /// it is queried.
42 class PhiValues {
43 public:
44   using ValueSet = SmallPtrSet<Value *, 4>;
45 
46   /// Construct an empty PhiValues.
47   PhiValues(const Function &F) : F(F) {}
48 
49   /// Get the underlying values of a phi.
50   ///
51   /// This returns the cached value if PN has previously been processed,
52   /// otherwise it processes it first.
53   const ValueSet &getValuesForPhi(const PHINode *PN);
54 
55   /// Notify PhiValues that the cached information using V is no longer valid
56   ///
57   /// Whenever a phi has its operands modified the cached values for that phi
58   /// (and the phis that use that phi) become invalid. A user of PhiValues has
59   /// to notify it of this by calling invalidateValue on either the operand or
60   /// the phi, which will then clear the relevant cached information.
61   void invalidateValue(const Value *V);
62 
63   /// Free the memory used by this class.
64   void releaseMemory();
65 
66   /// Print out the values currently in the cache.
67   void print(raw_ostream &OS) const;
68 
69   /// Handle invalidation events in the new pass manager.
70   bool invalidate(Function &, const PreservedAnalyses &,
71                   FunctionAnalysisManager::Invalidator &);
72 
73 private:
74   using PhiSet = SmallPtrSet<const PHINode *, 4>;
75   using ConstValueSet = SmallPtrSet<const Value *, 4>;
76 
77   /// The next depth number to be used by processPhi.
78   unsigned int NextDepthNumber = 1;
79 
80   /// Depth numbers of phis. Phis with the same depth number are part of the
81   /// same strongly connected component.
82   DenseMap<const PHINode *, unsigned int> DepthMap;
83 
84   /// Non-phi values reachable from each component.
85   DenseMap<unsigned int, ValueSet> NonPhiReachableMap;
86 
87   /// All values reachable from each component.
88   DenseMap<unsigned int, ConstValueSet> ReachableMap;
89 
90   /// A CallbackVH to notify PhiValues when a value is deleted or replaced, so
91   /// that the cached information for that value can be cleared to avoid
92   /// dangling pointers to invalid values.
93   class PhiValuesCallbackVH final : public CallbackVH {
94     PhiValues *PV;
95     void deleted() override;
96     void allUsesReplacedWith(Value *New) override;
97 
98   public:
99     PhiValuesCallbackVH(Value *V, PhiValues *PV = nullptr)
100         : CallbackVH(V), PV(PV) {}
101   };
102 
103   /// A set of callbacks to the values that processPhi has seen.
104   DenseSet<PhiValuesCallbackVH, DenseMapInfo<Value *>> TrackedValues;
105 
106   /// The function that the PhiValues is for.
107   const Function &F;
108 
109   /// Process a phi so that its entries in the depth and reachable maps are
110   /// fully populated.
111   void processPhi(const PHINode *PN, SmallVectorImpl<const PHINode *> &Stack);
112 };
113 
114 /// The analysis pass which yields a PhiValues
115 ///
116 /// The analysis does nothing by itself, and just returns an empty PhiValues
117 /// which will get filled in as it's used.
118 class PhiValuesAnalysis : public AnalysisInfoMixin<PhiValuesAnalysis> {
119   friend AnalysisInfoMixin<PhiValuesAnalysis>;
120   static AnalysisKey Key;
121 
122 public:
123   using Result = PhiValues;
124   PhiValues run(Function &F, FunctionAnalysisManager &);
125 };
126 
127 /// A pass for printing the PhiValues for a function.
128 ///
129 /// This pass doesn't print whatever information the PhiValues happens to hold,
130 /// but instead first uses the PhiValues to analyze all the phis in the function
131 /// so the complete information is printed.
132 class PhiValuesPrinterPass : public PassInfoMixin<PhiValuesPrinterPass> {
133   raw_ostream &OS;
134 
135 public:
136   explicit PhiValuesPrinterPass(raw_ostream &OS) : OS(OS) {}
137   PreservedAnalyses run(Function &F, FunctionAnalysisManager &AM);
138 };
139 
140 /// Wrapper pass for the legacy pass manager
141 class PhiValuesWrapperPass : public FunctionPass {
142   std::unique_ptr<PhiValues> Result;
143 
144 public:
145   static char ID;
146   PhiValuesWrapperPass();
147 
148   PhiValues &getResult() { return *Result; }
149   const PhiValues &getResult() const { return *Result; }
150 
151   bool runOnFunction(Function &F) override;
152   void releaseMemory() override;
153   void getAnalysisUsage(AnalysisUsage &AU) const override;
154 };
155 
156 } // namespace llvm
157 
158 #endif
159