[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

1 files changed, 9 insertions, 1 deletions

diff --git a/clang/lib/Frontend/InitPreprocessor.cpp b/clang/lib/Frontend/InitPreprocessor.cpp
index 9a0fdb1..9b611bf 100644
--- a/clang/lib/Frontend/InitPreprocessor.cpp
+++ b/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()));