1 //===- LiveVariables.h - Live Variable Analysis for Source CFGs -*- 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 implements Live Variables analysis for source-level CFGs.
10 //
11 //===----------------------------------------------------------------------===//
12 
13 #ifndef LLVM_CLANG_ANALYSIS_ANALYSES_LIVEVARIABLES_H
14 #define LLVM_CLANG_ANALYSIS_ANALYSES_LIVEVARIABLES_H
15 
16 #include "clang/AST/Decl.h"
17 #include "clang/Analysis/AnalysisDeclContext.h"
18 #include "llvm/ADT/ImmutableSet.h"
19 
20 namespace clang {
21 
22 class CFG;
23 class CFGBlock;
24 class Stmt;
25 class DeclRefExpr;
26 class SourceManager;
27 
28 class LiveVariables : public ManagedAnalysis {
29 public:
30   class LivenessValues {
31   public:
32 
33     llvm::ImmutableSet<const Expr *> liveExprs;
34     llvm::ImmutableSet<const VarDecl *> liveDecls;
35     llvm::ImmutableSet<const BindingDecl *> liveBindings;
36 
37     bool equals(const LivenessValues &V) const;
38 
LivenessValues()39     LivenessValues()
40       : liveExprs(nullptr), liveDecls(nullptr), liveBindings(nullptr) {}
41 
LivenessValues(llvm::ImmutableSet<const Expr * > liveExprs,llvm::ImmutableSet<const VarDecl * > LiveDecls,llvm::ImmutableSet<const BindingDecl * > LiveBindings)42     LivenessValues(llvm::ImmutableSet<const Expr *> liveExprs,
43                    llvm::ImmutableSet<const VarDecl *> LiveDecls,
44                    llvm::ImmutableSet<const BindingDecl *> LiveBindings)
45         : liveExprs(liveExprs), liveDecls(LiveDecls),
46           liveBindings(LiveBindings) {}
47 
48     bool isLive(const Expr *E) const;
49     bool isLive(const VarDecl *D) const;
50 
51     friend class LiveVariables;
52   };
53 
54   class Observer {
55     virtual void anchor();
56   public:
~Observer()57     virtual ~Observer() {}
58 
59     /// A callback invoked right before invoking the
60     ///  liveness transfer function on the given statement.
observeStmt(const Stmt * S,const CFGBlock * currentBlock,const LivenessValues & V)61     virtual void observeStmt(const Stmt *S,
62                              const CFGBlock *currentBlock,
63                              const LivenessValues& V) {}
64 
65     /// Called when the live variables analysis registers
66     /// that a variable is killed.
observerKill(const DeclRefExpr * DR)67     virtual void observerKill(const DeclRefExpr *DR) {}
68   };
69 
70   ~LiveVariables() override;
71 
72   /// Compute the liveness information for a given CFG.
73   static std::unique_ptr<LiveVariables>
74   computeLiveness(AnalysisDeclContext &analysisContext, bool killAtAssign);
75 
76   /// Return true if a variable is live at the end of a
77   /// specified block.
78   bool isLive(const CFGBlock *B, const VarDecl *D);
79 
80   /// Returns true if a variable is live at the beginning of the
81   ///  the statement.  This query only works if liveness information
82   ///  has been recorded at the statement level (see runOnAllBlocks), and
83   ///  only returns liveness information for block-level expressions.
84   bool isLive(const Stmt *S, const VarDecl *D);
85 
86   /// Returns true the block-level expression value is live
87   ///  before the given block-level expression (see runOnAllBlocks).
88   bool isLive(const Stmt *Loc, const Expr *Val);
89 
90   /// Print to stderr the variable liveness information associated with
91   /// each basic block.
92   void dumpBlockLiveness(const SourceManager &M);
93 
94   /// Print to stderr the expression liveness information associated with
95   /// each basic block.
96   void dumpExprLiveness(const SourceManager &M);
97 
98   void runOnAllBlocks(Observer &obs);
99 
100   static std::unique_ptr<LiveVariables>
create(AnalysisDeclContext & analysisContext)101   create(AnalysisDeclContext &analysisContext) {
102     return computeLiveness(analysisContext, true);
103   }
104 
105   static const void *getTag();
106 
107 private:
108   LiveVariables(void *impl);
109   void *impl;
110 };
111 
112 class RelaxedLiveVariables : public LiveVariables {
113 public:
114   static std::unique_ptr<LiveVariables>
create(AnalysisDeclContext & analysisContext)115   create(AnalysisDeclContext &analysisContext) {
116     return computeLiveness(analysisContext, false);
117   }
118 
119   static const void *getTag();
120 };
121 
122 } // end namespace clang
123 
124 #endif
125