[clang] [clang] Add __WCHAR_NATIVE_TYPE__ predefined macro (PR #203619)

Fri Jun 12 12:57:49 PDT 2026

llvmorg-github-actions[bot] wrote:




@llvm/pr-subscribers-clang

Author: Akira Hatanaka (ahatanak)

<details>
<summary>Changes</summary>

Define a new predefined macro __WCHAR_NATIVE_TYPE__ that expands to the platform's native type for wchar_t, i.e., the type wchar_t would have without -fshort-wchar. It matches __WCHAR_TYPE__ unless -fshort-wchar is in effect.

This lets code detect when wchar_t is different from its native type, for example to decide whether dispatching to a wchar_t-based runtime function such as wmemchr is safe (see llvm/llvm-project#195149).

rdar://175090927

---
Full diff: https://github.com/llvm/llvm-project/pull/203619.diff


7 Files Affected:

- (modified) clang/docs/LanguageExtensions.rst (+8) 
- (modified) clang/docs/ReleaseNotes.rst (+7) 
- (modified) clang/include/clang/Basic/TargetInfo.h (+12) 
- (modified) clang/lib/Basic/TargetInfo.cpp (+8) 
- (modified) clang/lib/Frontend/InitPreprocessor.cpp (+1) 
- (modified) clang/test/Preprocessor/init-aarch64.c (+1) 
- (modified) clang/test/Preprocessor/init.c (+1) 


``````````diff

diff --git a/clang/docs/LanguageExtensions.rst b/clang/docs/LanguageExtensions.rst
index fbb9947f39d3e..c0beb6ddecd02 100644
--- a/clang/docs/LanguageExtensions.rst
+++ b/clang/docs/LanguageExtensions.rst
@@ -393,6 +393,14 @@ Builtin Macros
   Defined to an integral value that is the include depth of the file currently
   being translated.  For the main file, this value is zero.
 
+``__WCHAR_NATIVE_TYPE__``
+  clang-specific extension defined to the platform's native type for
+  ``wchar_t``, i.e., the type ``wchar_t`` would have without ``-fshort-wchar``.
+  This matches ``__WCHAR_TYPE__`` unless ``-fshort-wchar`` is in effect. This
+  lets code detect when ``wchar_t`` is different from its native type,
+  e.g., to decide whether dispatching to a ``wchar_t``-based runtime function
+  such as ``wmemchr`` is safe.
+
 ``__TIMESTAMP__``
   Defined to the date and time of the last modification of the current source
   file.
diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index cf4826f50e5a5..12d09cb361825 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -312,6 +312,13 @@ Non-comprehensive list of changes in this release
 - ``typeid`` on references and pointers of ``final`` types no longer emits a
   vtable lookup at runtime.
 
+- Added a new predefined macro ``__WCHAR_NATIVE_TYPE__``, expanding to the
+  platform's native type for ``wchar_t`` (the type ``wchar_t`` would have
+  without ``-fshort-wchar``). It matches ``__WCHAR_TYPE__`` unless
+  ``-fshort-wchar`` is in effect, letting code detect when ``wchar_t`` is
+  different from its native type.
+
+
 - Updated support for Unicode from 15.1 to 18.0.
 
 New Compiler Flags
diff --git a/clang/include/clang/Basic/TargetInfo.h b/clang/include/clang/Basic/TargetInfo.h
index cc226403877e2..8615da60803f7 100644
--- a/clang/include/clang/Basic/TargetInfo.h
+++ b/clang/include/clang/Basic/TargetInfo.h
@@ -163,6 +163,11 @@ struct TransferrableTargetInfo {
       Char16Type, Char32Type, Int64Type, Int16Type, SigAtomicType,
       ProcessIDType;
 
+  /// The platform's native type for wchar_t, i.e., the type wchar_t would have
+  /// without -fshort-wchar. This matches WCharType unless -fshort-wchar is in
+  /// effect.
+  IntType WideCharNativeType;
+
   /// Whether Objective-C's built-in boolean type should be signed char.
   ///
   /// Otherwise, when this flag is not set, the normal built-in boolean type is
@@ -417,6 +422,13 @@ class TargetInfo : public TransferrableTargetInfo,
     return getCorrespondingUnsignedType(IntPtrType);
   }
   IntType getWCharType() const { return WCharType; }
+
+  /// Return the platform's native type for wchar_t, i.e., the type wchar_t
+  /// would have without -fshort-wchar.
+  IntType getWideCharNativeType() const {
+    return WideCharNativeType == NoInt ? WCharType : WideCharNativeType;
+  }
+
   IntType getWIntType() const { return WIntType; }
   IntType getChar16Type() const { return Char16Type; }
   IntType getChar32Type() const { return Char32Type; }
diff --git a/clang/lib/Basic/TargetInfo.cpp b/clang/lib/Basic/TargetInfo.cpp
index 854d23cadaea2..62fb6c8175484 100644
--- a/clang/lib/Basic/TargetInfo.cpp
+++ b/clang/lib/Basic/TargetInfo.cpp
@@ -137,6 +137,7 @@ TargetInfo::TargetInfo(const llvm::Triple &T) : Triple(T) {
   IntMaxType = SignedLongLong;
   IntPtrType = SignedLong;
   WCharType = SignedInt;
+  WideCharNativeType = NoInt;
   WIntType = SignedInt;
   Char16Type = UnsignedShort;
   Char32Type = UnsignedInt;
@@ -423,6 +424,13 @@ void TargetInfo::adjust(DiagnosticsEngine &Diags, LangOptions &Opts,
   if (Opts.NoBitFieldTypeAlign)
     UseBitFieldTypeAlignment = false;
 
+  // Capture the platform-native wchar_t before -fshort-wchar can override
+  // WCharType below. adjust() may run more than once on the same target, so
+  // only record it the first time, while WCharType still holds the target
+  // default.
+  if (WideCharNativeType == NoInt)
+    WideCharNativeType = WCharType;
+
   switch (Opts.WCharSize) {
   default: llvm_unreachable("invalid wchar_t width");
   case 0: break;
diff --git a/clang/lib/Frontend/InitPreprocessor.cpp b/clang/lib/Frontend/InitPreprocessor.cpp
index 3f0468a938149..f516c5159dba7 100644
--- a/clang/lib/Frontend/InitPreprocessor.cpp
+++ b/clang/lib/Frontend/InitPreprocessor.cpp
@@ -1168,6 +1168,7 @@ static void InitializePredefinedMacros(const TargetInfo &TI,
   DefineType("__SIZE_TYPE__", TI.getSizeType(), Builder);
   DefineFmt(LangOpts, "__SIZE", TI.getSizeType(), TI, Builder);
   DefineType("__WCHAR_TYPE__", TI.getWCharType(), Builder);
+  DefineType("__WCHAR_NATIVE_TYPE__", TI.getWideCharNativeType(), Builder);
   DefineType("__WINT_TYPE__", TI.getWIntType(), Builder);
   DefineTypeSizeAndWidth("__SIG_ATOMIC", TI.getSigAtomicType(), TI, Builder);
   if (LangOpts.C23)
diff --git a/clang/test/Preprocessor/init-aarch64.c b/clang/test/Preprocessor/init-aarch64.c
index 09e3fc926a309..3ec78a7651480 100644
--- a/clang/test/Preprocessor/init-aarch64.c
+++ b/clang/test/Preprocessor/init-aarch64.c
@@ -393,6 +393,7 @@
 // AARCH64-NEXT: #define __USER_LABEL_PREFIX__
 // AARCH64-NEXT: #define __VERSION__ "{{.*}}"
 // AARCH64-NEXT: #define __WCHAR_MAX__ 4294967295U
+// AARCH64-NEXT: #define __WCHAR_NATIVE_TYPE__ unsigned int
 // AARCH64-NEXT: #define __WCHAR_TYPE__ unsigned int
 // AARCH64-NEXT: #define __WCHAR_UNSIGNED__ 1
 // AARCH64-NEXT: #define __WCHAR_WIDTH__ 32
diff --git a/clang/test/Preprocessor/init.c b/clang/test/Preprocessor/init.c
index 80b7a6399e5f4..cc67db4fa068e 100644
--- a/clang/test/Preprocessor/init.c
+++ b/clang/test/Preprocessor/init.c
@@ -2076,6 +2076,7 @@
 // WEBASSEMBLY-NEXT:#define __USER_LABEL_PREFIX__
 // WEBASSEMBLY-NEXT:#define __VERSION__ "{{.*}}"
 // WEBASSEMBLY-NEXT:#define __WCHAR_MAX__ 2147483647
+// WEBASSEMBLY-NEXT:#define __WCHAR_NATIVE_TYPE__ int
 // WEBASSEMBLY-NEXT:#define __WCHAR_TYPE__ int
 // WEBASSEMBLY-NOT:#define __WCHAR_UNSIGNED__
 // WEBASSEMBLY-NEXT:#define __WCHAR_WIDTH__ 32

``````````

</details>


https://github.com/llvm/llvm-project/pull/203619
