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 //===- PhiValues.h - Phi Value Analysis -------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 //
 // This file defines the PhiValues class, and associated passes, which can be
 // used to find the underlying values of the phis in a function, i.e. the
 // non-phi values that can be found by traversing the phi graph.
 //
 // This information is computed lazily and cached. If new phis are added to the
 // function they are handled correctly, but if an existing phi has its operands
 // modified PhiValues has to be notified by calling invalidateValue.
 //
 //===----------------------------------------------------------------------===//
 
 #ifndef LLVM_ANALYSIS_PHIVALUES_H
 #define LLVM_ANALYSIS_PHIVALUES_H
 
 #include "llvm/ADT/DenseMap.h"
 #include "llvm/ADT/DenseSet.h"
 #include "llvm/ADT/SetVector.h"
 #include "llvm/IR/PassManager.h"
 #include "llvm/IR/ValueHandle.h"
 #include "llvm/Pass.h"
 
 namespace llvm {
 
 class Value;
 class PHINode;
 class Function;
 
 /// Class for calculating and caching the underlying values of phis in a
 /// function.
 ///
 /// Initially the PhiValues is empty, and gets incrementally populated whenever
 /// it is queried.
 class PhiValues {
 public:
   using ValueSet = SmallSetVector<Value *, 4>;
 
   /// Construct an empty PhiValues.
   PhiValues(const Function &F) : F(F) {}
 
   /// Get the underlying values of a phi.
   ///
   /// This returns the cached value if PN has previously been processed,
   /// otherwise it processes it first.
   const ValueSet &getValuesForPhi(const PHINode *PN);
 
   /// Notify PhiValues that the cached information using V is no longer valid
   ///
   /// Whenever a phi has its operands modified the cached values for that phi
   /// (and the phis that use that phi) become invalid. A user of PhiValues has
   /// to notify it of this by calling invalidateValue on either the operand or
   /// the phi, which will then clear the relevant cached information.
   void invalidateValue(const Value *V);
 
   /// Free the memory used by this class.
   void releaseMemory();
 
   /// Print out the values currently in the cache.
   void print(raw_ostream &OS) const;
 
   /// Handle invalidation events in the new pass manager.
   bool invalidate(Function &, const PreservedAnalyses &,
                   FunctionAnalysisManager::Invalidator &);
 
 private:
   using ConstValueSet = SmallSetVector<const Value *, 4>;
 
   /// The next depth number to be used by processPhi.
   unsigned int NextDepthNumber = 1;
 
   /// Depth numbers of phis. Phis with the same depth number are part of the
   /// same strongly connected component.
   DenseMap<const PHINode *, unsigned int> DepthMap;
 
   /// Non-phi values reachable from each component.
   DenseMap<unsigned int, ValueSet> NonPhiReachableMap;
 
   /// All values reachable from each component.
   DenseMap<unsigned int, ConstValueSet> ReachableMap;
 
   /// A CallbackVH to notify PhiValues when a value is deleted or replaced, so
   /// that the cached information for that value can be cleared to avoid
   /// dangling pointers to invalid values.
   class PhiValuesCallbackVH final : public CallbackVH {
     PhiValues *PV;
     void deleted() override;
     void allUsesReplacedWith(Value *New) override;
 
   public:
     PhiValuesCallbackVH(Value *V, PhiValues *PV = nullptr)
         : CallbackVH(V), PV(PV) {}
   };
 
   /// A set of callbacks to the values that processPhi has seen.
   DenseSet<PhiValuesCallbackVH, DenseMapInfo<Value *>> TrackedValues;
 
   /// The function that the PhiValues is for.
   const Function &F;
 
   /// Process a phi so that its entries in the depth and reachable maps are
   /// fully populated.
   void processPhi(const PHINode *PN, SmallVectorImpl<const PHINode *> &Stack);
 };
 
 /// The analysis pass which yields a PhiValues
 ///
 /// The analysis does nothing by itself, and just returns an empty PhiValues
 /// which will get filled in as it's used.
 class PhiValuesAnalysis : public AnalysisInfoMixin<PhiValuesAnalysis> {
   friend AnalysisInfoMixin<PhiValuesAnalysis>;
   static AnalysisKey Key;
 
 public:
   using Result = PhiValues;
   PhiValues run(Function &F, FunctionAnalysisManager &);
 };
 
 /// A pass for printing the PhiValues for a function.
 ///
 /// This pass doesn't print whatever information the PhiValues happens to hold,
 /// but instead first uses the PhiValues to analyze all the phis in the function
 /// so the complete information is printed.
 class PhiValuesPrinterPass : public PassInfoMixin<PhiValuesPrinterPass> {
   raw_ostream &OS;
 
 public:
   explicit PhiValuesPrinterPass(raw_ostream &OS) : OS(OS) {}
   PreservedAnalyses run(Function &F, FunctionAnalysisManager &AM);
   static bool isRequired() { return true; }
 };
 
 /// Wrapper pass for the legacy pass manager
 class PhiValuesWrapperPass : public FunctionPass {
   std::unique_ptr<PhiValues> Result;
 
 public:
   static char ID;
   PhiValuesWrapperPass();
 
   PhiValues &getResult() { return *Result; }
   const PhiValues &getResult() const { return *Result; }
 
   bool runOnFunction(Function &F) override;
   void releaseMemory() override;
   void getAnalysisUsage(AnalysisUsage &AU) const override;
 };
 
 } // namespace llvm
 
 #endif

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