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diff --git a/clang-tools-extra/clang-tidy/llvm/PreferIsaOrDynCastInConditionalsCheck.h b/clang-tools-extra/clang-tidy/llvm/PreferIsaOrDynCastInConditionalsCheck.h
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+++ b/clang-tools-extra/clang-tidy/llvm/PreferIsaOrDynCastInConditionalsCheck.h
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+//===--- PreferIsaOrDynCastInConditionalsCheck.h - clang-tidy ---*- 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
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_LLVM_AVOIDCASTINCONDITIONALCHECK_H
+#define LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_LLVM_AVOIDCASTINCONDITIONALCHECK_H
+
+#include "../ClangTidyCheck.h"
+
+namespace clang {
+namespace tidy {
+namespace llvm {
+
+/// \brief Looks at conditionals and finds and replaces cases of ``cast<>``, which will
+/// assert rather than return a null pointer, and ``dyn_cast<>`` where
+/// the return value is not captured.  Additionally, finds and replaces cases that match the
+/// pattern ``var && isa<X>(var)``, where ``var`` is evaluated twice.
+///
+/// Finds cases like these:
+/// \code
+///  if (auto x = cast<X>(y)) {}
+///  // is replaced by:
+///  if (auto x = dyn_cast<X>(y)) {}
+///
+///  if (cast<X>(y)) {}
+///  // is replaced by:
+///  if (isa<X>(y)) {}
+///
+///  if (dyn_cast<X>(y)) {}
+///  // is replaced by:
+///  if (isa<X>(y)) {}
+///
+///  if (var && isa<T>(var)) {}
+///  // is replaced by:
+///  if (isa_and_nonnull<T>(var.foo())) {}
+/// \endcode
+///
+///  // Other cases are ignored, e.g.:
+/// \code
+///  if (auto f = cast<Z>(y)->foo()) {}
+///  if (cast<Z>(y)->foo()) {}
+///  if (X.cast(y)) {}
+/// \endcode
+///
+/// For the user-facing documentation see:
+/// http://clang.llvm.org/extra/clang-tidy/checks/llvm-prefer-isa-or-dyn-cast-in-conditionals.html
+class PreferIsaOrDynCastInConditionalsCheck : public ClangTidyCheck {
+public:
+  PreferIsaOrDynCastInConditionalsCheck(StringRef Name,
+                                        ClangTidyContext *Context)
+      : ClangTidyCheck(Name, Context) {}
+  void registerMatchers(ast_matchers::MatchFinder *Finder) override;
+  void check(const ast_matchers::MatchFinder::MatchResult &Result) override;
+};
+
+} // namespace llvm
+} // namespace tidy
+} // namespace clang
+
+#endif // LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_LLVM_AVOIDCASTINCONDITIONALCHECK_H