10 files changed, 53 insertions, 20 deletions
diff --git a/clang/lib/Headers/__stddef_null.h b/clang/lib/Headers/__stddef_null.h
index 7336fdab3897..c10bd2d7d988 100644
--- a/clang/lib/Headers/__stddef_null.h
+++ b/clang/lib/Headers/__stddef_null.h
@@ -7,7 +7,7 @@
  *===-----------------------------------------------------------------------===
  */
 
-#if !defined(NULL) || !__has_feature(modules)
+#if !defined(NULL) || !__building_module(_Builtin_stddef)
 
 /* linux/stddef.h will define NULL to 0. glibc (and other) headers then define
  * __need_NULL and rely on stddef.h to redefine NULL to the correct value again.
diff --git a/clang/lib/Headers/__stddef_nullptr_t.h b/clang/lib/Headers/__stddef_nullptr_t.h
index 183d394d56c1..7f3fbe6fe0d3 100644
--- a/clang/lib/Headers/__stddef_nullptr_t.h
+++ b/clang/lib/Headers/__stddef_nullptr_t.h
@@ -7,7 +7,12 @@
  *===-----------------------------------------------------------------------===
  */
 
-#ifndef _NULLPTR_T
+/*
+ * When -fbuiltin-headers-in-system-modules is set this is a non-modular header
+ * and needs to behave as if it was textual.
+ */
+#if !defined(_NULLPTR_T) ||                                                    \
+    (__has_feature(modules) && !__building_module(_Builtin_stddef))
 #define _NULLPTR_T
 
 #ifdef __cplusplus
diff --git a/clang/lib/Headers/__stddef_offsetof.h b/clang/lib/Headers/__stddef_offsetof.h
index 3b347b3b92f6..84172c6cd273 100644
--- a/clang/lib/Headers/__stddef_offsetof.h
+++ b/clang/lib/Headers/__stddef_offsetof.h
@@ -7,6 +7,11 @@
  *===-----------------------------------------------------------------------===
  */
 
-#ifndef offsetof
+/*
+ * When -fbuiltin-headers-in-system-modules is set this is a non-modular header
+ * and needs to behave as if it was textual.
+ */
+#if !defined(offsetof) ||                                                      \
+    (__has_feature(modules) && !__building_module(_Builtin_stddef))
 #define offsetof(t, d) __builtin_offsetof(t, d)
 #endif
diff --git a/clang/lib/Headers/__stddef_ptrdiff_t.h b/clang/lib/Headers/__stddef_ptrdiff_t.h
index 3ea6d7d2852e..fd3c893c66c9 100644
--- a/clang/lib/Headers/__stddef_ptrdiff_t.h
+++ b/clang/lib/Headers/__stddef_ptrdiff_t.h
@@ -7,7 +7,12 @@
  *===-----------------------------------------------------------------------===
  */
 
-#ifndef _PTRDIFF_T
+/*
+ * When -fbuiltin-headers-in-system-modules is set this is a non-modular header
+ * and needs to behave as if it was textual.
+ */
+#if !defined(_PTRDIFF_T) ||                                                    \
+    (__has_feature(modules) && !__building_module(_Builtin_stddef))
 #define _PTRDIFF_T
 
 typedef __PTRDIFF_TYPE__ ptrdiff_t;
diff --git a/clang/lib/Headers/__stddef_rsize_t.h b/clang/lib/Headers/__stddef_rsize_t.h
index b6428d0c12b6..dd433d40d973 100644
--- a/clang/lib/Headers/__stddef_rsize_t.h
+++ b/clang/lib/Headers/__stddef_rsize_t.h
@@ -7,7 +7,12 @@
  *===-----------------------------------------------------------------------===
  */
 
-#ifndef _RSIZE_T
+/*
+ * When -fbuiltin-headers-in-system-modules is set this is a non-modular header
+ * and needs to behave as if it was textual.
+ */
+#if !defined(_RSIZE_T) ||                                                      \
+    (__has_feature(modules) && !__building_module(_Builtin_stddef))
 #define _RSIZE_T
 
 typedef __SIZE_TYPE__ rsize_t;
diff --git a/clang/lib/Headers/__stddef_size_t.h b/clang/lib/Headers/__stddef_size_t.h
index e4a389510bcd..3dd7b1f37929 100644
--- a/clang/lib/Headers/__stddef_size_t.h
+++ b/clang/lib/Headers/__stddef_size_t.h
@@ -7,7 +7,12 @@
  *===-----------------------------------------------------------------------===
  */
 
-#ifndef _SIZE_T
+/*
+ * When -fbuiltin-headers-in-system-modules is set this is a non-modular header
+ * and needs to behave as if it was textual.
+ */
+#if !defined(_SIZE_T) ||                                                       \
+    (__has_feature(modules) && !__building_module(_Builtin_stddef))
 #define _SIZE_T
 
 typedef __SIZE_TYPE__ size_t;
diff --git a/clang/lib/Headers/__stddef_unreachable.h b/clang/lib/Headers/__stddef_unreachable.h
index 3e7fe0197966..518580c92d3f 100644
--- a/clang/lib/Headers/__stddef_unreachable.h
+++ b/clang/lib/Headers/__stddef_unreachable.h
@@ -7,6 +7,11 @@
  *===-----------------------------------------------------------------------===
  */
 
-#ifndef unreachable
+/*
+ * When -fbuiltin-headers-in-system-modules is set this is a non-modular header
+ * and needs to behave as if it was textual.
+ */
+#if !defined(unreachable) ||                                                   \
+    (__has_feature(modules) && !__building_module(_Builtin_stddef))
 #define unreachable() __builtin_unreachable()
 #endif
diff --git a/clang/lib/Headers/__stddef_wchar_t.h b/clang/lib/Headers/__stddef_wchar_t.h
index 16a6186512c0..bd69f6322541 100644
--- a/clang/lib/Headers/__stddef_wchar_t.h
+++ b/clang/lib/Headers/__stddef_wchar_t.h
@@ -9,7 +9,12 @@
 
 #if !defined(__cplusplus) || (defined(_MSC_VER) && !_NATIVE_WCHAR_T_DEFINED)
 
-#ifndef _WCHAR_T
+/*
+ * When -fbuiltin-headers-in-system-modules is set this is a non-modular header
+ * and needs to behave as if it was textual.
+ */
+#if !defined(_WCHAR_T) ||                                                      \
+    (__has_feature(modules) && !__building_module(_Builtin_stddef))
 #define _WCHAR_T
 
 #ifdef _MSC_EXTENSIONS
diff --git a/clang/lib/Headers/larchintrin.h b/clang/lib/Headers/larchintrin.h
index a613e5ca0e5e..f4218295919a 100644
--- a/clang/lib/Headers/larchintrin.h
+++ b/clang/lib/Headers/larchintrin.h
@@ -156,7 +156,7 @@ extern __inline unsigned char
   return (unsigned char)__builtin_loongarch_iocsrrd_b((unsigned int)_1);
 }
 
-extern __inline unsigned char
+extern __inline unsigned short
     __attribute__((__gnu_inline__, __always_inline__, __artificial__))
     __iocsrrd_h(unsigned int _1) {
   return (unsigned short)__builtin_loongarch_iocsrrd_h((unsigned int)_1);
diff --git a/clang/lib/Headers/module.modulemap b/clang/lib/Headers/module.modulemap
index a786689d3917..56a13f69bc05 100644
--- a/clang/lib/Headers/module.modulemap
+++ b/clang/lib/Headers/module.modulemap
@@ -155,9 +155,9 @@ module _Builtin_intrinsics [system] [extern_c] {
 
 // Start -fbuiltin-headers-in-system-modules affected modules
 
-// The following modules all ignore their top level headers
-// when -fbuiltin-headers-in-system-modules is passed, and
-// most of those headers join system modules when present.
+// The following modules all ignore their headers when
+// -fbuiltin-headers-in-system-modules is passed, and many of
+// those headers join system modules when present.
 
 // e.g. if -fbuiltin-headers-in-system-modules is passed, then
 // float.h will not be in the _Builtin_float module (that module
@@ -190,11 +190,6 @@ module _Builtin_stdalign [system] {
   export *
 }
 
-// When -fbuiltin-headers-in-system-modules is passed, only
-// the top level headers are removed, the implementation headers
-// will always be in their submodules. That means when stdarg.h
-// is included, it will still import this module and make the
-// appropriate submodules visible.
 module _Builtin_stdarg [system] {
   textual header "stdarg.h"
 
@@ -237,6 +232,8 @@ module _Builtin_stdbool [system] {
 module _Builtin_stddef [system] {
   textual header "stddef.h"
 
+  // __stddef_max_align_t.h is always in this module, even if
+  // -fbuiltin-headers-in-system-modules is passed.
   explicit module max_align_t {
     header "__stddef_max_align_t.h"
     export *
@@ -283,9 +280,10 @@ module _Builtin_stddef [system] {
   }
 }
 
-/* wint_t is provided by <wchar.h> and not <stddef.h>. It's here
- * for compatibility, but must be explicitly requested. Therefore
- * __stddef_wint_t.h is not part of _Builtin_stddef. */
+// wint_t is provided by <wchar.h> and not <stddef.h>. It's here
+// for compatibility, but must be explicitly requested. Therefore
+// __stddef_wint_t.h is not part of _Builtin_stddef. It is always in
+// this module even if -fbuiltin-headers-in-system-modules is passed.
 module _Builtin_stddef_wint_t [system] {
   header "__stddef_wint_t.h"
   export *