1 //===--- VarBypassDetector.cpp - Bypass jumps detector ------------*- 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 contains VarBypassDetector class, which is used to detect
11 // local variable declarations which can be bypassed by jumps.
12 //
13 //===----------------------------------------------------------------------===//
14 
15 #ifndef LLVM_CLANG_LIB_CODEGEN_VARBYPASSDETECTOR_H
16 #define LLVM_CLANG_LIB_CODEGEN_VARBYPASSDETECTOR_H
17 
18 #include "llvm/ADT/DenseMap.h"
19 #include "llvm/ADT/DenseSet.h"
20 #include "llvm/ADT/SmallVector.h"
21 
22 namespace clang {
23 
24 class Decl;
25 class Stmt;
26 class VarDecl;
27 
28 namespace CodeGen {
29 
30 /// The class detects jumps which bypass local variables declaration:
31 ///    goto L;
32 ///    int a;
33 ///  L:
34 ///
35 /// This is simplified version of JumpScopeChecker. Primary differences:
36 ///  * Detects only jumps into the scope local variables.
37 ///  * Does not detect jumps out of the scope of local variables.
38 ///  * Not limited to variables with initializers, JumpScopeChecker is limited.
39 class VarBypassDetector {
40   // Scope information. Contains a parent scope and related variable
41   // declaration.
42   llvm::SmallVector<std::pair<unsigned, const VarDecl *>, 48> Scopes;
43   // List of jumps with scopes.
44   llvm::SmallVector<std::pair<const Stmt *, unsigned>, 16> FromScopes;
45   // Lookup map to find scope for destinations.
46   llvm::DenseMap<const Stmt *, unsigned> ToScopes;
47   // Set of variables which were bypassed by some jump.
48   llvm::DenseSet<const VarDecl *> Bypasses;
49   // If true assume that all variables are being bypassed.
50   bool AlwaysBypassed = false;
51 
52 public:
53   void Init(const Stmt *Body);
54 
55   /// Returns true if the variable declaration was by bypassed by any goto or
56   /// switch statement.
57   bool IsBypassed(const VarDecl *D) const {
58     return AlwaysBypassed || Bypasses.find(D) != Bypasses.end();
59   }
60 
61 private:
62   bool BuildScopeInformation(const Decl *D, unsigned &ParentScope);
63   bool BuildScopeInformation(const Stmt *S, unsigned &origParentScope);
64   void Detect();
65   void Detect(unsigned From, unsigned To);
66 };
67 }
68 }
69 
70 #endif
71