1 files changed, 3 insertions, 0 deletions
diff --git a/lib/AST/Decl.cpp b/lib/AST/Decl.cpp
index 2987e7c276..aeffd0a240 100644
--- a/lib/AST/Decl.cpp
+++ b/lib/AST/Decl.cpp
@@ -1761,6 +1761,9 @@ bool FunctionDecl::isReservedGlobalPlacementOperator() const {
 }
 
 bool FunctionDecl::hasCLanguageLinkage() const {
+  // Users expect to be able to write
+  // extern "C" void *__builtin_alloca (size_t);
+  // so consider builtins as having C language linkage.
   if (getBuiltinID())
     return true;