diff --git a/clang/lib/Sema/SemaChecking.cpp b/clang/lib/Sema/SemaChecking.cpp
index f9f82cd..436e17a 100644
--- a/clang/lib/Sema/SemaChecking.cpp
+++ b/clang/lib/Sema/SemaChecking.cpp
@@ -1179,6 +1179,10 @@
   case Builtin::BI__builtin_alloca_with_align:
     if (SemaBuiltinAllocaWithAlign(TheCall))
       return ExprError();
+    LLVM_FALLTHROUGH;
+  case Builtin::BI__builtin_alloca:
+    Diag(TheCall->getBeginLoc(), diag::warn_alloca)
+        << TheCall->getDirectCallee();
     break;
   case Builtin::BI__assume:
   case Builtin::BI__builtin_assume: