LiveVariables.h

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//===- LiveVariables.h - Live Variable Analysis for Source CFGs -*- 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 implements Live Variables analysis for source-level CFGs.
//
//===----------------------------------------------------------------------===//
 
#ifndef LLVM_CLANG_ANALYSIS_ANALYSES_LIVEVARIABLES_H
#define LLVM_CLANG_ANALYSIS_ANALYSES_LIVEVARIABLES_H
 
#include "clang/AST/Decl.h"
#include "clang/Analysis/AnalysisDeclContext.h"
#include "llvm/ADT/ImmutableSet.h"
 
namespace clang {
 
class CFG;
class CFGBlock;
class Stmt;
class DeclRefExpr;
class SourceManager;
 
class LiveVariables : public ManagedAnalysis {
public:
  // Canonicalization of these sets is a major performance loss here, so the
  // non-canonicalizing form is selected at compile time.
  template <typename T>
  using SetTy =
      llvm::ImmutableSet<T, llvm::ImutContainerInfo<T>, /*Canonicalize=*/false>;
 
  class LivenessValues {
  public:
    SetTy<const Expr *> liveExprs;
    SetTy<const VarDecl *> liveDecls;
    SetTy<const BindingDecl *> liveBindings;
 
    bool operator==(const LivenessValues &V) const;
 
    LivenessValues()
      : liveExprs(nullptr), liveDecls(nullptr), liveBindings(nullptr) {}
 
    LivenessValues(SetTy<const Expr *> liveExprs,
                   SetTy<const VarDecl *> LiveDecls,
                   SetTy<const BindingDecl *> LiveBindings)
        : liveExprs(liveExprs), liveDecls(LiveDecls),
          liveBindings(LiveBindings) {}
 
    bool isLive(const Expr *E) const;
    bool isLive(const VarDecl *D) const;
 
    friend class LiveVariables;
  };
 
  class Observer {
    virtual void anchor();
  public:
    virtual ~Observer() {}
 
    /// A callback invoked right before invoking the
    ///  liveness transfer function on the given statement.
    virtual void observeStmt(const Stmt *S, const CFGBlock *currentBlock,
                             const LivenessValues &V) {}
  };
 
  ~LiveVariables() override;
 
  /// Compute the liveness information for a given CFG.
  static std::unique_ptr<LiveVariables>
  computeLiveness(AnalysisDeclContext &analysisContext, bool killAtAssign);
 
  /// Return true if a variable is live at the end of a
  /// specified block.
  bool isLive(const CFGBlock *B, const VarDecl *D);
 
  /// Returns true if a variable is live at the beginning of the
  ///  the statement.  This query only works if liveness information
  ///  has been recorded at the statement level (see runOnAllBlocks), and
  ///  only returns liveness information for block-level expressions.
  bool isLive(const Stmt *S, const VarDecl *D);
 
  /// Returns true the block-level expression value is live
  ///  before the given block-level expression (see runOnAllBlocks).
  bool isLive(const Stmt *Loc, const Expr *Val);
 
  /// Print to stderr the variable liveness information associated with
  /// each basic block.
  void dumpBlockLiveness(const SourceManager &M);
 
  /// Print to stderr the expression liveness information associated with
  /// each basic block.
  void dumpExprLiveness(const SourceManager &M);
 
  void runOnAllBlocks(Observer &obs);
 
  static std::unique_ptr<LiveVariables>
  create(AnalysisDeclContext &analysisContext) {
    return computeLiveness(analysisContext, true);
  }
 
  static const void *getTag();
 
private:
  LiveVariables(void *impl);
  void *impl;
};
 
class RelaxedLiveVariables : public LiveVariables {
public:
  static std::unique_ptr<LiveVariables>
  create(AnalysisDeclContext &analysisContext) {
    return computeLiveness(analysisContext, false);
  }
 
  static const void *getTag();
};
 
} // end namespace clang
 
#endif