clang  6.0.0svn
ThreadSafetyLogical.cpp
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1 //===- ThreadSafetyLogical.cpp ---------------------------------*- 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 // This file defines a representation for logical expressions with SExpr leaves
10 // that are used as part of fact-checking capability expressions.
11 //===----------------------------------------------------------------------===//
12 
14 
15 using namespace llvm;
16 using namespace clang::threadSafety::lexpr;
17 
18 // Implication. We implement De Morgan's Laws by maintaining LNeg and RNeg
19 // to keep track of whether LHS and RHS are negated.
20 static bool implies(const LExpr *LHS, bool LNeg, const LExpr *RHS, bool RNeg) {
21  // In comments below, we write => for implication.
22 
23  // Calculates the logical AND implication operator.
24  const auto LeftAndOperator = [=](const BinOp *A) {
25  return implies(A->left(), LNeg, RHS, RNeg) &&
26  implies(A->right(), LNeg, RHS, RNeg);
27  };
28  const auto RightAndOperator = [=](const BinOp *A) {
29  return implies(LHS, LNeg, A->left(), RNeg) &&
30  implies(LHS, LNeg, A->right(), RNeg);
31  };
32 
33  // Calculates the logical OR implication operator.
34  const auto LeftOrOperator = [=](const BinOp *A) {
35  return implies(A->left(), LNeg, RHS, RNeg) ||
36  implies(A->right(), LNeg, RHS, RNeg);
37  };
38  const auto RightOrOperator = [=](const BinOp *A) {
39  return implies(LHS, LNeg, A->left(), RNeg) ||
40  implies(LHS, LNeg, A->right(), RNeg);
41  };
42 
43  // Recurse on right.
44  switch (RHS->kind()) {
45  case LExpr::And:
46  // When performing right recursion:
47  // C => A & B [if] C => A and C => B
48  // When performing right recursion (negated):
49  // C => !(A & B) [if] C => !A | !B [===] C => !A or C => !B
50  return RNeg ? RightOrOperator(cast<And>(RHS))
51  : RightAndOperator(cast<And>(RHS));
52  case LExpr::Or:
53  // When performing right recursion:
54  // C => (A | B) [if] C => A or C => B
55  // When performing right recursion (negated):
56  // C => !(A | B) [if] C => !A & !B [===] C => !A and C => !B
57  return RNeg ? RightAndOperator(cast<Or>(RHS))
58  : RightOrOperator(cast<Or>(RHS));
59  case LExpr::Not:
60  // Note that C => !A is very different from !(C => A). It would be incorrect
61  // to return !implies(LHS, RHS).
62  return implies(LHS, LNeg, cast<Not>(RHS)->exp(), !RNeg);
63  case LExpr::Terminal:
64  // After reaching the terminal, it's time to recurse on the left.
65  break;
66  }
67 
68  // RHS is now a terminal. Recurse on Left.
69  switch (LHS->kind()) {
70  case LExpr::And:
71  // When performing left recursion:
72  // A & B => C [if] A => C or B => C
73  // When performing left recursion (negated):
74  // !(A & B) => C [if] !A | !B => C [===] !A => C and !B => C
75  return LNeg ? LeftAndOperator(cast<And>(LHS))
76  : LeftOrOperator(cast<And>(LHS));
77  case LExpr::Or:
78  // When performing left recursion:
79  // A | B => C [if] A => C and B => C
80  // When performing left recursion (negated):
81  // !(A | B) => C [if] !A & !B => C [===] !A => C or !B => C
82  return LNeg ? LeftOrOperator(cast<Or>(LHS))
83  : LeftAndOperator(cast<Or>(LHS));
84  case LExpr::Not:
85  // Note that A => !C is very different from !(A => C). It would be incorrect
86  // to return !implies(LHS, RHS).
87  return implies(cast<Not>(LHS)->exp(), !LNeg, RHS, RNeg);
88  case LExpr::Terminal:
89  // After reaching the terminal, it's time to perform identity comparisons.
90  break;
91  }
92 
93  // A => A
94  // !A => !A
95  if (LNeg != RNeg)
96  return false;
97 
98  // FIXME -- this should compare SExprs for equality, not pointer equality.
99  return cast<Terminal>(LHS)->expr() == cast<Terminal>(RHS)->expr();
100 }
101 
102 namespace clang {
103 namespace threadSafety {
104 namespace lexpr {
105 
106 bool implies(const LExpr *LHS, const LExpr *RHS) {
107  // Start out by assuming that LHS and RHS are not negated.
108  return ::implies(LHS, false, RHS, false);
109 }
110 }
111 }
112 }
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const internal::VariadicDynCastAllOfMatcher< Stmt, Expr > expr
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static bool implies(const LExpr *LHS, bool LNeg, const LExpr *RHS, bool RNeg)
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