Index: clang-tools-extra/clang-tidy/readability/FunctionCognitiveComplexityCheck.cpp
===================================================================
--- clang-tools-extra/clang-tidy/readability/FunctionCognitiveComplexityCheck.cpp
+++ clang-tools-extra/clang-tidy/readability/FunctionCognitiveComplexityCheck.cpp
@@ -501,9 +501,9 @@
 
 void FunctionCognitiveComplexityCheck::registerMatchers(MatchFinder *Finder) {
   Finder->addMatcher(
-      functionDecl(
-          allOf(isDefinition(), unless(anyOf(isDefaulted(), isDeleted(),
-                                             isImplicit(), isInstantiated()))))
+      functionDecl(isDefinition(),
+                   unless(anyOf(isDefaulted(), isDeleted(), isImplicit(),
+                                isInstantiated(), isWeak())))
           .bind("func"),
       this);
 }
Index: clang-tools-extra/test/clang-tidy/checkers/readability-function-cognitive-complexity.cpp
===================================================================
--- clang-tools-extra/test/clang-tidy/checkers/readability-function-cognitive-complexity.cpp
+++ clang-tools-extra/test/clang-tidy/checkers/readability-function-cognitive-complexity.cpp
@@ -1013,3 +1013,5 @@
 
   templatedFunction<void*>();
 }
+
+static void pr47779_dont_crash_on_weak() __attribute__((__weakref__("__pr47779_dont_crash_on_weak")));
Index: clang/include/clang/ASTMatchers/ASTMatchers.h
===================================================================
--- clang/include/clang/ASTMatchers/ASTMatchers.h
+++ clang/include/clang/ASTMatchers/ASTMatchers.h
@@ -4647,6 +4647,17 @@
   return Node.isDefaulted();
 }
 
+/// Matches weak function declarations.
+///
+/// Given:
+/// \code
+///   void foo() __attribute__((__weakref__("__foo")));
+///   void bar();
+/// \endcode
+/// functionDecl(isWeak())
+///   matches the weak declaration foo, but not bar.
+AST_MATCHER(FunctionDecl, isWeak) { return Node.isWeak(); }
+
 /// Matches functions that have a dynamic exception specification.
 ///
 /// Given: