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      1 //===--- VarBypassDetector.h - Bypass jumps detector --------------*- 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 contains VarBypassDetector class, which is used to detect
     10 // local variable declarations which can be bypassed by jumps.
     11 //
     12 //===----------------------------------------------------------------------===//
     13 
     14 #ifndef LLVM_CLANG_LIB_CODEGEN_VARBYPASSDETECTOR_H
     15 #define LLVM_CLANG_LIB_CODEGEN_VARBYPASSDETECTOR_H
     16 
     17 #include "clang/AST/Decl.h"
     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