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112 lines
4.1 KiB
C++
112 lines
4.1 KiB
C++
//===- ThreadSafetyLogical.cpp ---------------------------------*- C++ --*-===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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// This file defines a representation for logical expressions with SExpr leaves
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// that are used as part of fact-checking capability expressions.
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//===----------------------------------------------------------------------===//
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#include "clang/Analysis/Analyses/ThreadSafetyLogical.h"
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using namespace llvm;
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using namespace clang::threadSafety::lexpr;
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// Implication. We implement De Morgan's Laws by maintaining LNeg and RNeg
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// to keep track of whether LHS and RHS are negated.
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static bool implies(const LExpr *LHS, bool LNeg, const LExpr *RHS, bool RNeg) {
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// In comments below, we write => for implication.
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// Calculates the logical AND implication operator.
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const auto LeftAndOperator = [=](const BinOp *A) {
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return implies(A->left(), LNeg, RHS, RNeg) &&
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implies(A->right(), LNeg, RHS, RNeg);
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};
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const auto RightAndOperator = [=](const BinOp *A) {
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return implies(LHS, LNeg, A->left(), RNeg) &&
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implies(LHS, LNeg, A->right(), RNeg);
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};
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// Calculates the logical OR implication operator.
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const auto LeftOrOperator = [=](const BinOp *A) {
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return implies(A->left(), LNeg, RHS, RNeg) ||
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implies(A->right(), LNeg, RHS, RNeg);
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};
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const auto RightOrOperator = [=](const BinOp *A) {
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return implies(LHS, LNeg, A->left(), RNeg) ||
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implies(LHS, LNeg, A->right(), RNeg);
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};
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// Recurse on right.
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switch (RHS->kind()) {
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case LExpr::And:
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// When performing right recursion:
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// C => A & B [if] C => A and C => B
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// When performing right recursion (negated):
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// C => !(A & B) [if] C => !A | !B [===] C => !A or C => !B
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return RNeg ? RightOrOperator(cast<And>(RHS))
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: RightAndOperator(cast<And>(RHS));
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case LExpr::Or:
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// When performing right recursion:
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// C => (A | B) [if] C => A or C => B
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// When performing right recursion (negated):
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// C => !(A | B) [if] C => !A & !B [===] C => !A and C => !B
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return RNeg ? RightAndOperator(cast<Or>(RHS))
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: RightOrOperator(cast<Or>(RHS));
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case LExpr::Not:
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// Note that C => !A is very different from !(C => A). It would be incorrect
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// to return !implies(LHS, RHS).
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return implies(LHS, LNeg, cast<Not>(RHS)->exp(), !RNeg);
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case LExpr::Terminal:
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// After reaching the terminal, it's time to recurse on the left.
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break;
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}
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// RHS is now a terminal. Recurse on Left.
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switch (LHS->kind()) {
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case LExpr::And:
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// When performing left recursion:
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// A & B => C [if] A => C or B => C
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// When performing left recursion (negated):
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// !(A & B) => C [if] !A | !B => C [===] !A => C and !B => C
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return LNeg ? LeftAndOperator(cast<And>(LHS))
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: LeftOrOperator(cast<And>(LHS));
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case LExpr::Or:
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// When performing left recursion:
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// A | B => C [if] A => C and B => C
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// When performing left recursion (negated):
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// !(A | B) => C [if] !A & !B => C [===] !A => C or !B => C
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return LNeg ? LeftOrOperator(cast<Or>(LHS))
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: LeftAndOperator(cast<Or>(LHS));
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case LExpr::Not:
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// Note that A => !C is very different from !(A => C). It would be incorrect
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// to return !implies(LHS, RHS).
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return implies(cast<Not>(LHS)->exp(), !LNeg, RHS, RNeg);
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case LExpr::Terminal:
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// After reaching the terminal, it's time to perform identity comparisons.
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break;
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}
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// A => A
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// !A => !A
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if (LNeg != RNeg)
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return false;
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// FIXME -- this should compare SExprs for equality, not pointer equality.
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return cast<Terminal>(LHS)->expr() == cast<Terminal>(RHS)->expr();
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}
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namespace clang {
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namespace threadSafety {
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namespace lexpr {
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bool implies(const LExpr *LHS, const LExpr *RHS) {
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// Start out by assuming that LHS and RHS are not negated.
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return ::implies(LHS, false, RHS, false);
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}
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}
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}
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}
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