[clang] [clang][Sema] Don't warn for implicit uses of builtins in system headers (PR #138205)

[Nick Sarnie via cfe-commits]

https://github.com/sarnex created https://github.com/llvm/llvm-project/pull/138205

Running CI

>From c66ec11d8170a0e4c0b2fc50bdae039fd9c208fb Mon Sep 17 00:00:00 2001
From: "Sarnie, Nick" <nick.sarnie at intel.com>
Date: Thu, 1 May 2025 14:47:45 -0700
Subject: [PATCH] [clang][Sema] Don't warn for implicit uses of builtins in
 system headers

Signed-off-by: Sarnie, Nick <nick.sarnie at intel.com>
---
 clang/lib/Sema/SemaDecl.cpp                    | 7 ++++++-
 clang/test/Sema/Inputs/builtin-system-header.h | 1 +
 clang/test/Sema/builtin-system-header.c        | 8 ++++++++
 3 files changed, 15 insertions(+), 1 deletion(-)
 create mode 100644 clang/test/Sema/Inputs/builtin-system-header.h
 create mode 100644 clang/test/Sema/builtin-system-header.c

diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index a3285e8f6f5a2..37008f9eb3235 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -2376,9 +2376,14 @@ NamedDecl *Sema::LazilyCreateBuiltin(IdentifierInfo *II, unsigned ID,
     return nullptr;
   }
 
+  // Warn for implicit uses of header dependent libraries,
+  // except in system headers.
   if (!ForRedeclaration &&
       (Context.BuiltinInfo.isPredefinedLibFunction(ID) ||
-       Context.BuiltinInfo.isHeaderDependentFunction(ID))) {
+       Context.BuiltinInfo.isHeaderDependentFunction(ID)) &&
+      (!getDiagnostics().getSuppressSystemWarnings() ||
+       !Context.getSourceManager().isInSystemHeader(
+           Context.getSourceManager().getSpellingLoc(Loc)))) {
     Diag(Loc, LangOpts.C99 ? diag::ext_implicit_lib_function_decl_c99
                            : diag::ext_implicit_lib_function_decl)
         << Context.BuiltinInfo.getName(ID) << R;
diff --git a/clang/test/Sema/Inputs/builtin-system-header.h b/clang/test/Sema/Inputs/builtin-system-header.h
new file mode 100644
index 0000000000000..ebd5655e6f8ef
--- /dev/null
+++ b/clang/test/Sema/Inputs/builtin-system-header.h
@@ -0,0 +1 @@
+#define MACRO(x,y) _InterlockedOr64(x,y);
diff --git a/clang/test/Sema/builtin-system-header.c b/clang/test/Sema/builtin-system-header.c
new file mode 100644
index 0000000000000..83c3c15e314a7
--- /dev/null
+++ b/clang/test/Sema/builtin-system-header.c
@@ -0,0 +1,8 @@
+// RUN: %clang_cc1 -fms-extensions -fsyntax-only -verify -triple arm64-windows -isystem %S/Inputs %s
+
+// expected-no-diagnostics
+#include <builtin-system-header.h>
+
+void foo() {
+  MACRO(0,0);
+}