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