[C23] Fixed the value of BOOL_WIDTH (#117364)

The standard mandates that this returns the width of the type, which is
the number of bits in the value. For bool, that's required to be `1`
explicitly.

Fixes #117348

Author: AaronBallman

clang/docs/ReleaseNotes.rst

@@ -332,6 +332,8 @@ C23 Feature Support
 
 - Clang now supports `N3029 <https://www.open-std.org/jtc1/sc22/wg14/www/docs/n3029.htm>`_ Improved Normal Enumerations.
 - Clang now officially supports `N3030 <https://www.open-std.org/jtc1/sc22/wg14/www/docs/n3030.htm>`_ Enhancements to Enumerations. Clang already supported it as an extension, so there were no changes to compiler behavior.
+- Fixed the value of ``BOOL_WIDTH`` in ``<limits.h>`` to return ``1``
+  explicitly, as mandated by the standard. Fixes #GH117348
 
 Non-comprehensive list of changes in this release
 -------------------------------------------------

clang/lib/Frontend/InitPreprocessor.cpp

@@ -1103,7 +1103,15 @@ static void InitializePredefinedMacros(const TargetInfo &TI,
   assert(TI.getCharWidth() == 8 && "Only support 8-bit char so far");
   Builder.defineMacro("__CHAR_BIT__", Twine(TI.getCharWidth()));
 
-  Builder.defineMacro("__BOOL_WIDTH__", Twine(TI.getBoolWidth()));
+  // The macro is specifying the number of bits in the width, not the number of
+  // bits the object requires for its in-memory representation, which is what
+  // getBoolWidth() will return. The bool/_Bool data type is only ever one bit
+  // wide. See C23 6.2.6.2p2 for the rules in C. Note that
+  // C++23 [basic.fundamental]p10 allows an implementation-defined value
+  // representation for bool; when lowering to LLVM, Clang represents bool as an
+  // i8 in memory but as an i1 when the value is needed, so '1' is also correct
+  // for C++.
+  Builder.defineMacro("__BOOL_WIDTH__", "1");
   Builder.defineMacro("__SHRT_WIDTH__", Twine(TI.getShortWidth()));
   Builder.defineMacro("__INT_WIDTH__", Twine(TI.getIntWidth()));
   Builder.defineMacro("__LONG_WIDTH__", Twine(TI.getLongWidth()));

clang/test/C/C23/n2412.c

@@ -0,0 +1,27 @@
+// RUN: %clang_cc1 -verify -std=c23 -ffreestanding %s
+
+/* WG14 N2412: Clang 14
+ * Two's complement sign representation
+ */
+// expected-no-diagnostics
+
+#include <limits.h>
+
+// GH117348 -- BOOL_WIDTH was accidentally expanding to the number of bits in
+// the object representation (8) rather than the number of bits in the value
+// representation (1).
+static_assert(BOOL_WIDTH == 1);
+
+// Validate the other macro requirements.
+static_assert(CHAR_WIDTH == SCHAR_WIDTH);
+static_assert(CHAR_WIDTH == UCHAR_WIDTH);
+static_assert(CHAR_WIDTH == CHAR_BIT);
+
+static_assert(USHRT_WIDTH >= 16);
+static_assert(UINT_WIDTH >= 16);
+static_assert(ULONG_WIDTH >= 32);
+static_assert(ULLONG_WIDTH >= 64);
+static_assert(BITINT_MAXWIDTH >= ULLONG_WIDTH);
+
+static_assert(MB_LEN_MAX >= 1);
+

clang/test/Preprocessor/init-aarch64.c

@@ -44,7 +44,7 @@
 // AARCH64:      #define __BIGGEST_ALIGNMENT__ 16
 // AARCH64_BE-NEXT: #define __BIG_ENDIAN__ 1
 // AARCH64-NEXT: #define __BITINT_MAXWIDTH__ 128
-// AARCH64-NEXT: #define __BOOL_WIDTH__ 8
+// AARCH64-NEXT: #define __BOOL_WIDTH__ 1
 // AARCH64_BE-NEXT: #define __BYTE_ORDER__ __ORDER_BIG_ENDIAN__
 // AARCH64_LE-NEXT: #define __BYTE_ORDER__ __ORDER_LITTLE_ENDIAN__
 // AARCH64-NEXT: #define __CHAR16_TYPE__ unsigned short
@@ -785,7 +785,7 @@
 // ARM64EC-MSVC: #define __ATOMIC_SEQ_CST 5
 // ARM64EC-MSVC: #define __BIGGEST_ALIGNMENT__ 16
 // ARM64EC-MSVC: #define __BITINT_MAXWIDTH__ 128
-// ARM64EC-MSVC: #define __BOOL_WIDTH__ 8
+// ARM64EC-MSVC: #define __BOOL_WIDTH__ 1
 // ARM64EC-MSVC: #define __BYTE_ORDER__ __ORDER_LITTLE_ENDIAN__
 // ARM64EC-MSVC: #define __CHAR16_TYPE__ unsigned short
 // ARM64EC-MSVC: #define __CHAR32_TYPE__ unsigned int

clang/test/Preprocessor/init-loongarch.c

@@ -25,7 +25,7 @@
 // LA32-NEXT: #define __ATOMIC_SEQ_CST 5
 // LA32: #define __BIGGEST_ALIGNMENT__ 16
 // LA32: #define __BITINT_MAXWIDTH__ 128
-// LA32: #define __BOOL_WIDTH__ 8
+// LA32: #define __BOOL_WIDTH__ 1
 // LA32: #define __BYTE_ORDER__ __ORDER_LITTLE_ENDIAN__
 // LA32: #define __CHAR16_TYPE__ unsigned short
 // LA32: #define __CHAR32_TYPE__ unsigned int
@@ -346,7 +346,7 @@
 // LA64-NEXT: #define __ATOMIC_SEQ_CST 5
 // LA64: #define __BIGGEST_ALIGNMENT__ 16
 // LA64: #define __BITINT_MAXWIDTH__ 128
-// LA64: #define __BOOL_WIDTH__ 8
+// LA64: #define __BOOL_WIDTH__ 1
 // LA64: #define __BYTE_ORDER__ __ORDER_LITTLE_ENDIAN__
 // LA64: #define __CHAR16_TYPE__ unsigned short
 // LA64: #define __CHAR32_TYPE__ unsigned int

clang/test/Preprocessor/init.c

@@ -1617,7 +1617,7 @@
 // WEBASSEMBLY-NEXT:#define __ATOMIC_SEQ_CST 5
 // WEBASSEMBLY-NEXT:#define __BIGGEST_ALIGNMENT__ 16
 // WEBASSEMBLY-NEXT:#define __BITINT_MAXWIDTH__ 128
-// WEBASSEMBLY-NEXT:#define __BOOL_WIDTH__ 8
+// WEBASSEMBLY-NEXT:#define __BOOL_WIDTH__ 1
 // WEBASSEMBLY-NEXT:#define __BYTE_ORDER__ __ORDER_LITTLE_ENDIAN__
 // WEBASSEMBLY-NEXT:#define __CHAR16_TYPE__ unsigned short
 // WEBASSEMBLY-NEXT:#define __CHAR32_TYPE__ unsigned int