[clang] [Clang] [C23] Implement N2653: u8 strings are char8_t[] (PR #97208)
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Sun Jun 30 04:41:32 PDT 2024
llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-backend-x86
Author: Mital Ashok (MitalAshok)
<details>
<summary>Changes</summary>
https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2653.htm
Closes #<!-- -->97202
---
Full diff: https://github.com/llvm/llvm-project/pull/97208.diff
7 Files Affected:
- (modified) clang/docs/ReleaseNotes.rst (+6)
- (modified) clang/include/clang/Basic/DiagnosticSemaKinds.td (+4-1)
- (modified) clang/lib/Frontend/InitPreprocessor.cpp (+4-2)
- (modified) clang/lib/Headers/stdatomic.h (+5)
- (modified) clang/lib/Sema/SemaExpr.cpp (+16-7)
- (added) clang/test/C/C2x/n2653.c (+29)
- (modified) clang/www/c_status.html (+1-1)
``````````diff
diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index c720e47dbe35b..e51be81d8b11a 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -337,6 +337,12 @@ C23 Feature Support
- Properly promote bit-fields of bit-precise integer types to the field's type
rather than to ``int``. #GH87641
+- Compiler support for `N2653 char8_t: A type for UTF-8 characters and strings`
+ <https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2653.htm>`_: ``u8`` string
+ literals are now of type ``char8_t[N]`` in C23 and expose
+ ``__CLANG_ATOMIC_CHAR8_T_LOCK_FREE``/``__GCC_ATOMIC_CHAR8_T_LOCK_FREE`` to
+ implement the corresponding macro in ``<stdatomic.h>``.
+
Non-comprehensive list of changes in this release
-------------------------------------------------
diff --git a/clang/include/clang/Basic/DiagnosticSemaKinds.td b/clang/include/clang/Basic/DiagnosticSemaKinds.td
index 5dc36c594bcb7..6a00b92df1c36 100644
--- a/clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -7252,7 +7252,10 @@ def err_array_init_utf8_string_into_char : Error<
def warn_cxx20_compat_utf8_string : Warning<
"type of UTF-8 string literal will change from array of const char to "
"array of const char8_t in C++20">, InGroup<CXX20Compat>, DefaultIgnore;
-def note_cxx20_compat_utf8_string_remove_u8 : Note<
+def warn_c23_compat_utf8_string : Warning<
+ "type of UTF-8 string literal will change from array of char to "
+ "array of char8_t in C23">, InGroup<C23Compat>, DefaultIgnore;
+def note_cxx20_c23_compat_utf8_string_remove_u8 : Note<
"remove 'u8' prefix to avoid a change of behavior; "
"Clang encodes unprefixed narrow string literals as UTF-8">;
def err_array_init_different_type : Error<
diff --git a/clang/lib/Frontend/InitPreprocessor.cpp b/clang/lib/Frontend/InitPreprocessor.cpp
index 55ec460064830..6270c37342bcf 100644
--- a/clang/lib/Frontend/InitPreprocessor.cpp
+++ b/clang/lib/Frontend/InitPreprocessor.cpp
@@ -1342,8 +1342,10 @@ static void InitializePredefinedMacros(const TargetInfo &TI,
getLockFreeValue(TI.get##Type##Width(), TI));
DEFINE_LOCK_FREE_MACRO(BOOL, Bool);
DEFINE_LOCK_FREE_MACRO(CHAR, Char);
- if (LangOpts.Char8)
- DEFINE_LOCK_FREE_MACRO(CHAR8_T, Char); // Treat char8_t like char.
+ // char8_t has the same representation / width as unsigned
+ // char in C++ and is a typedef for unsigned char in C23
+ if (LangOpts.Char8 || LangOpts.C23)
+ DEFINE_LOCK_FREE_MACRO(CHAR8_T, Char);
DEFINE_LOCK_FREE_MACRO(CHAR16_T, Char16);
DEFINE_LOCK_FREE_MACRO(CHAR32_T, Char32);
DEFINE_LOCK_FREE_MACRO(WCHAR_T, WChar);
diff --git a/clang/lib/Headers/stdatomic.h b/clang/lib/Headers/stdatomic.h
index 9c103d98af8c5..c33cd8083525c 100644
--- a/clang/lib/Headers/stdatomic.h
+++ b/clang/lib/Headers/stdatomic.h
@@ -35,6 +35,10 @@ extern "C" {
#define ATOMIC_BOOL_LOCK_FREE __CLANG_ATOMIC_BOOL_LOCK_FREE
#define ATOMIC_CHAR_LOCK_FREE __CLANG_ATOMIC_CHAR_LOCK_FREE
+#if (defined(__STDC_VERSION__) && __STDC_VERSION__ >= 202311L) || \
+ defined(__cplusplus)
+#define ATOMIC_CHAR8_T_LOCK_FREE __CLANG_ATOMIC_CHAR8_T_LOCK_FREE
+#endif
#define ATOMIC_CHAR16_T_LOCK_FREE __CLANG_ATOMIC_CHAR16_T_LOCK_FREE
#define ATOMIC_CHAR32_T_LOCK_FREE __CLANG_ATOMIC_CHAR32_T_LOCK_FREE
#define ATOMIC_WCHAR_T_LOCK_FREE __CLANG_ATOMIC_WCHAR_T_LOCK_FREE
@@ -104,6 +108,7 @@ typedef _Atomic(long) atomic_long;
typedef _Atomic(unsigned long) atomic_ulong;
typedef _Atomic(long long) atomic_llong;
typedef _Atomic(unsigned long long) atomic_ullong;
+typedef _Atomic(unsigned char) atomic_char8_t;
typedef _Atomic(uint_least16_t) atomic_char16_t;
typedef _Atomic(uint_least32_t) atomic_char32_t;
typedef _Atomic(wchar_t) atomic_wchar_t;
diff --git a/clang/lib/Sema/SemaExpr.cpp b/clang/lib/Sema/SemaExpr.cpp
index db44cfe1288b6..a1b060f7f1510 100644
--- a/clang/lib/Sema/SemaExpr.cpp
+++ b/clang/lib/Sema/SemaExpr.cpp
@@ -2082,6 +2082,8 @@ Sema::ActOnStringLiteral(ArrayRef<Token> StringToks, Scope *UDLScope) {
} else if (Literal.isUTF8()) {
if (getLangOpts().Char8)
CharTy = Context.Char8Ty;
+ else if (getLangOpts().C23)
+ CharTy = Context.UnsignedCharTy;
Kind = StringLiteralKind::UTF8;
} else if (Literal.isUTF16()) {
CharTy = Context.Char16Ty;
@@ -2093,17 +2095,24 @@ Sema::ActOnStringLiteral(ArrayRef<Token> StringToks, Scope *UDLScope) {
CharTy = Context.UnsignedCharTy;
}
- // Warn on initializing an array of char from a u8 string literal; this
- // becomes ill-formed in C++2a.
- if (getLangOpts().CPlusPlus && !getLangOpts().CPlusPlus20 &&
- !getLangOpts().Char8 && Kind == StringLiteralKind::UTF8) {
- Diag(StringTokLocs.front(), diag::warn_cxx20_compat_utf8_string);
+ // Warn on u8 string literals before C++20 and C23, whose type
+ // was an array of char before but becomes an array of char8_t.
+ // In C++20, initializing an array of char from a u8 string literal
+ // becomes ill-formed. In C23, it might have an unexpected value if
+ // char was signed.
+ if (Kind == StringLiteralKind::UTF8 &&
+ (getLangOpts().CPlusPlus
+ ? !getLangOpts().CPlusPlus20 && !getLangOpts().Char8
+ : !getLangOpts().C23)) {
+ Diag(StringTokLocs.front(), getLangOpts().CPlusPlus
+ ? diag::warn_cxx20_compat_utf8_string
+ : diag::warn_c23_compat_utf8_string);
// Create removals for all 'u8' prefixes in the string literal(s). This
- // ensures C++2a compatibility (but may change the program behavior when
+ // ensures C++20/C23 compatibility (but may change the program behavior when
// built by non-Clang compilers for which the execution character set is
// not always UTF-8).
- auto RemovalDiag = PDiag(diag::note_cxx20_compat_utf8_string_remove_u8);
+ auto RemovalDiag = PDiag(diag::note_cxx20_c23_compat_utf8_string_remove_u8);
SourceLocation RemovalDiagLoc;
for (const Token &Tok : StringToks) {
if (Tok.getKind() == tok::utf8_string_literal) {
diff --git a/clang/test/C/C2x/n2653.c b/clang/test/C/C2x/n2653.c
new file mode 100644
index 0000000000000..1abd61947de7e
--- /dev/null
+++ b/clang/test/C/C2x/n2653.c
@@ -0,0 +1,29 @@
+// RUN: %clang_cc1 -verify=c23 -std=c23 %s
+// RUN: %clang_cc1 -verify=c17 -std=c17 %s
+
+// c23-no-diagnostics
+
+#include <stdatomic.h>
+
+#define __enable_constant_folding(x) (__builtin_constant_p(x) ? (x) : (x))
+
+#ifndef ATOMIC_CHAR8_T_LOCK_FREE
+#error missing
+#endif
+// c17-error at -2 {{missing}}
+
+_Static_assert(_Generic(u8"", unsigned char*: 1, char*: 0), "");
+// c17-error at -1 {{static assertion failed}}
+
+// -fsigned-char is the default
+#define M(X) __enable_constant_folding((X) >= 0x80)
+
+_Static_assert(M(u8"\U000000E9"[0]), "");
+// c17-error at -1 {{static assertion failed}}
+#if __STDC_VERSION__ >= 202311L
+_Static_assert(M(u8'\xC3'), "");
+#endif
+
+const char cu8[] = u8"text";
+const signed char scu8[] = u8"text";
+const unsigned char ucu8[] = u8"text";
diff --git a/clang/www/c_status.html b/clang/www/c_status.html
index 84cd8e836006c..81bb51a58e5cb 100644
--- a/clang/www/c_status.html
+++ b/clang/www/c_status.html
@@ -1061,7 +1061,7 @@ <h2 id="c2x">C23 implementation status</h2>
<tr>
<td>char8_t: A type for UTF-8 characters and strings</td>
<td><a href="https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2653.htm">N2653</a></td>
- <td class="none" align="center">No</td>
+ <td class="unreleased" align="center">Clang 19</td>
</tr>
<tr>
<td>Clarification for max exponent macros-update</td>
``````````
</details>
https://github.com/llvm/llvm-project/pull/97208
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