1 files changed, 15 insertions, 0 deletions
diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index 984a14ad50d..1650a11222c 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -11878,6 +11878,21 @@ Decl *Sema::ActOnFinishFunctionBody(Decl *dcl, Stmt *Body,
                 << FixItHint::CreateInsertion(FTL.getRParenLoc(), "void");
         }
       }
+
+      // GNU warning -Wstrict-prototypes
+      //   Warn if K&R function is defined without a previous declaration.
+      //   This warning is issued only if the definition itself does not provide
+      //   a prototype. Only K&R definitions do not provide a prototype.
+      //   An empty list in a function declarator that is part of a definition
+      //   of that function specifies that the function has no parameters
+      //   (C99 6.7.5.3p14)
+      if (!FD->hasWrittenPrototype() && FD->getNumParams() > 0 &&
+          !LangOpts.CPlusPlus) {
+        TypeSourceInfo *TI = FD->getTypeSourceInfo();
+        TypeLoc TL = TI->getTypeLoc();
+        FunctionTypeLoc FTL = TL.castAs<FunctionTypeLoc>();
+        Diag(FTL.getLParenLoc(), diag::warn_strict_prototypes) << 1;
+      }
     }
 
     if (auto *MD = dyn_cast<CXXMethodDecl>(FD)) {