1 //===- PhiValues.h - Phi Value Analysis -------------------------*- C++ -*-===//
2 //
3 //                     The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 // This file defines the PhiValues class, and associated passes, which can be
11 // used to find the underlying values of the phis in a function, i.e. the
12 // non-phi values that can be found by traversing the phi graph.
13 //
14 // This information is computed lazily and cached. If new phis are added to the
15 // function they are handled correctly, but if an existing phi has its operands
16 // modified PhiValues has to be notified by calling invalidateValue.
17 //
18 //===----------------------------------------------------------------------===//
19 
20 #ifndef LLVM_ANALYSIS_PHIVALUES_H
21 #define LLVM_ANALYSIS_PHIVALUES_H
22 
23 #include "llvm/ADT/DenseMap.h"
24 #include "llvm/ADT/DenseSet.h"
25 #include "llvm/ADT/SmallPtrSet.h"
26 #include "llvm/ADT/SmallVector.h"
27 #include "llvm/IR/PassManager.h"
28 #include "llvm/IR/ValueHandle.h"
29 #include "llvm/Pass.h"
30 
31 namespace llvm {
32 
33 class Use;
34 class Value;
35 class PHINode;
36 class Function;
37 
38 /// Class for calculating and caching the underlying values of phis in a
39 /// function.
40 ///
41 /// Initially the PhiValues is empty, and gets incrementally populated whenever
42 /// it is queried.
43 class PhiValues {
44 public:
45   using ValueSet = SmallPtrSet<Value *, 4>;
46 
47   /// Construct an empty PhiValues.
PhiValues(const Function & F)48   PhiValues(const Function &F) : F(F) {}
49 
50   /// Get the underlying values of a phi.
51   ///
52   /// This returns the cached value if PN has previously been processed,
53   /// otherwise it processes it first.
54   const ValueSet &getValuesForPhi(const PHINode *PN);
55 
56   /// Notify PhiValues that the cached information using V is no longer valid
57   ///
58   /// Whenever a phi has its operands modified the cached values for that phi
59   /// (and the phis that use that phi) become invalid. A user of PhiValues has
60   /// to notify it of this by calling invalidateValue on either the operand or
61   /// the phi, which will then clear the relevant cached information.
62   void invalidateValue(const Value *V);
63 
64   /// Free the memory used by this class.
65   void releaseMemory();
66 
67   /// Print out the values currently in the cache.
68   void print(raw_ostream &OS) const;
69 
70   /// Handle invalidation events in the new pass manager.
71   bool invalidate(Function &, const PreservedAnalyses &,
72                   FunctionAnalysisManager::Invalidator &);
73 
74 private:
75   using PhiSet = SmallPtrSet<const PHINode *, 4>;
76   using ConstValueSet = SmallPtrSet<const Value *, 4>;
77 
78   /// The next depth number to be used by processPhi.
79   unsigned int NextDepthNumber = 1;
80 
81   /// Depth numbers of phis. Phis with the same depth number are part of the
82   /// same strongly connected component.
83   DenseMap<const PHINode *, unsigned int> DepthMap;
84 
85   /// Non-phi values reachable from each component.
86   DenseMap<unsigned int, ValueSet> NonPhiReachableMap;
87 
88   /// All values reachable from each component.
89   DenseMap<unsigned int, ConstValueSet> ReachableMap;
90 
91   /// A CallbackVH to notify PhiValues when a value is deleted or replaced, so
92   /// that the cached information for that value can be cleared to avoid
93   /// dangling pointers to invalid values.
94   class PhiValuesCallbackVH final : public CallbackVH {
95     PhiValues *PV;
96     void deleted() override;
97     void allUsesReplacedWith(Value *New) override;
98 
99   public:
100     PhiValuesCallbackVH(Value *V, PhiValues *PV = nullptr)
CallbackVH(V)101         : CallbackVH(V), PV(PV) {}
102   };
103 
104   /// A set of callbacks to the values that processPhi has seen.
105   DenseSet<PhiValuesCallbackVH, DenseMapInfo<Value *>> TrackedValues;
106 
107   /// The function that the PhiValues is for.
108   const Function &F;
109 
110   /// Process a phi so that its entries in the depth and reachable maps are
111   /// fully populated.
112   void processPhi(const PHINode *PN, SmallVector<const PHINode *, 8> &Stack);
113 };
114 
115 /// The analysis pass which yields a PhiValues
116 ///
117 /// The analysis does nothing by itself, and just returns an empty PhiValues
118 /// which will get filled in as it's used.
119 class PhiValuesAnalysis : public AnalysisInfoMixin<PhiValuesAnalysis> {
120   friend AnalysisInfoMixin<PhiValuesAnalysis>;
121   static AnalysisKey Key;
122 
123 public:
124   using Result = PhiValues;
125   PhiValues run(Function &F, FunctionAnalysisManager &);
126 };
127 
128 /// A pass for printing the PhiValues for a function.
129 ///
130 /// This pass doesn't print whatever information the PhiValues happens to hold,
131 /// but instead first uses the PhiValues to analyze all the phis in the function
132 /// so the complete information is printed.
133 class PhiValuesPrinterPass : public PassInfoMixin<PhiValuesPrinterPass> {
134   raw_ostream &OS;
135 
136 public:
PhiValuesPrinterPass(raw_ostream & OS)137   explicit PhiValuesPrinterPass(raw_ostream &OS) : OS(OS) {}
138   PreservedAnalyses run(Function &F, FunctionAnalysisManager &AM);
139 };
140 
141 /// Wrapper pass for the legacy pass manager
142 class PhiValuesWrapperPass : public FunctionPass {
143   std::unique_ptr<PhiValues> Result;
144 
145 public:
146   static char ID;
147   PhiValuesWrapperPass();
148 
getResult()149   PhiValues &getResult() { return *Result; }
getResult()150   const PhiValues &getResult() const { return *Result; }
151 
152   bool runOnFunction(Function &F) override;
153   void releaseMemory() override;
154   void getAnalysisUsage(AnalysisUsage &AU) const override;
155 };
156 
157 } // namespace llvm
158 
159 #endif
160