[libcxx-commits] [libcxx] [libc++] Simplify the implementation of iostream.cpp (PR #124103)

[Louis Dionne via libcxx-commits]

================
@@ -7,90 +7,53 @@
 //===----------------------------------------------------------------------===//
 
 #include "std_stream.h"
-#include <__locale>
-#include <new>
-#include <string>
 
-#define _str(s) #s
-#define str(s) _str(s)
-#define _LIBCPP_ABI_NAMESPACE_STR str(_LIBCPP_ABI_NAMESPACE)
+#include <__memory/construct_at.h>
+#include <__ostream/basic_ostream.h>
+#include <istream>
 
-_LIBCPP_BEGIN_NAMESPACE_STD
-
-alignas(istream) _LIBCPP_EXPORTED_FROM_ABI char cin[sizeof(istream)]
-#if defined(_LIBCPP_ABI_MICROSOFT) && defined(__clang__)
-    __asm__("?cin@" _LIBCPP_ABI_NAMESPACE_STR "@std@@3V?$basic_istream at DU?$char_traits at D@" _LIBCPP_ABI_NAMESPACE_STR
-            "@std@@@12 at A")
-#endif
-        ;
-alignas(__stdinbuf<char>) static char __cin[sizeof(__stdinbuf<char>)];
-static mbstate_t mb_cin;
+#define ABI_NAMESPACE_STR _LIBCPP_TOSTRING(_LIBCPP_ABI_NAMESPACE)
 
-#if _LIBCPP_HAS_WIDE_CHARACTERS
-alignas(wistream) _LIBCPP_EXPORTED_FROM_ABI char wcin[sizeof(wistream)]
-#  if defined(_LIBCPP_ABI_MICROSOFT) && defined(__clang__)
-    __asm__("?wcin@" _LIBCPP_ABI_NAMESPACE_STR "@std@@3V?$basic_istream at _WU?$char_traits at _W@" _LIBCPP_ABI_NAMESPACE_STR
-            "@std@@@12 at A")
-#  endif
-        ;
-alignas(__stdinbuf<wchar_t>) static char __wcin[sizeof(__stdinbuf<wchar_t>)];
-static mbstate_t mb_wcin;
-#endif // _LIBCPP_HAS_WIDE_CHARACTERS
-
-alignas(ostream) _LIBCPP_EXPORTED_FROM_ABI char cout[sizeof(ostream)]
-#if defined(_LIBCPP_ABI_MICROSOFT) && defined(__clang__)
-    __asm__("?cout@" _LIBCPP_ABI_NAMESPACE_STR "@std@@3V?$basic_ostream at DU?$char_traits at D@" _LIBCPP_ABI_NAMESPACE_STR
-            "@std@@@12 at A")
-#endif
-        ;
-alignas(__stdoutbuf<char>) static char __cout[sizeof(__stdoutbuf<char>)];
-static mbstate_t mb_cout;
-
-#if _LIBCPP_HAS_WIDE_CHARACTERS
-alignas(wostream) _LIBCPP_EXPORTED_FROM_ABI char wcout[sizeof(wostream)]
-#  if defined(_LIBCPP_ABI_MICROSOFT) && defined(__clang__)
-    __asm__("?wcout@" _LIBCPP_ABI_NAMESPACE_STR "@std@@3V?$basic_ostream at _WU?$char_traits at _W@" _LIBCPP_ABI_NAMESPACE_STR
-            "@std@@@12 at A")
-#  endif
-        ;
-alignas(__stdoutbuf<wchar_t>) static char __wcout[sizeof(__stdoutbuf<wchar_t>)];
-static mbstate_t mb_wcout;
-#endif // _LIBCPP_HAS_WIDE_CHARACTERS
-
-alignas(ostream) _LIBCPP_EXPORTED_FROM_ABI char cerr[sizeof(ostream)]
-#if defined(_LIBCPP_ABI_MICROSOFT) && defined(__clang__)
-    __asm__("?cerr@" _LIBCPP_ABI_NAMESPACE_STR "@std@@3V?$basic_ostream at DU?$char_traits at D@" _LIBCPP_ABI_NAMESPACE_STR
-            "@std@@@12 at A")
-#endif
-        ;
-alignas(__stdoutbuf<char>) static char __cerr[sizeof(__stdoutbuf<char>)];
-static mbstate_t mb_cerr;
+_LIBCPP_BEGIN_NAMESPACE_STD
 
-#if _LIBCPP_HAS_WIDE_CHARACTERS
-alignas(wostream) _LIBCPP_EXPORTED_FROM_ABI char wcerr[sizeof(wostream)]
-#  if defined(_LIBCPP_ABI_MICROSOFT) && defined(__clang__)
-    __asm__("?wcerr@" _LIBCPP_ABI_NAMESPACE_STR "@std@@3V?$basic_ostream at _WU?$char_traits at _W@" _LIBCPP_ABI_NAMESPACE_STR
-            "@std@@@12 at A")
-#  endif
-        ;
-alignas(__stdoutbuf<wchar_t>) static char __wcerr[sizeof(__stdoutbuf<wchar_t>)];
-static mbstate_t mb_wcerr;
-#endif // _LIBCPP_HAS_WIDE_CHARACTERS
+template <class StreamT, class BufferT>
+union stream_data {
+  stream_data() {}
+  ~stream_data() {}
+  struct {
+    StreamT stream;
+    BufferT buffer;
+    mbstate_t mb;
+  };
+
+  void init(FILE* stdstream) {
+    std::construct_at(&buffer, stdstream, &mb);
+    std::construct_at(&stream, &buffer);
+  }
+};
 
-alignas(ostream) _LIBCPP_EXPORTED_FROM_ABI char clog[sizeof(ostream)]
-#if defined(_LIBCPP_ABI_MICROSOFT) && defined(__clang__)
-    __asm__("?clog@" _LIBCPP_ABI_NAMESPACE_STR "@std@@3V?$basic_ostream at DU?$char_traits at D@" _LIBCPP_ABI_NAMESPACE_STR
-            "@std@@@12 at A")
+#define CHAR_MANGLING_char "D"
+#define CHAR_MANGLING_wchar_t "_W"
+#define CHAR_MANGLING(CharT) CHAR_MANGLING_##CharT
+
+#ifdef _LIBCPP_ABI_MICROSOFT
+#  define STREAM(StreamT, BufferT, CharT, var)                                                                         \
+    stream_data<StreamT<CharT>, BufferT<CharT>> var __asm__(                                                           \
+        "?" #var "@" ABI_NAMESPACE_STR "@std@@3V?$" #StreamT                                                           \
+        "@" CHAR_MANGLING(CharT) "U?$char_traits@" CHAR_MANGLING(CharT) "@" ABI_NAMESPACE_STR "@std@@@12 at A")
+#else
+#  define STREAM(StreamT, BufferT, CharT, var) stream_data<StreamT<CharT>, BufferT<CharT>> var
 #endif
-        ;
 
+_LIBCPP_EXPORTED_FROM_ABI STREAM(basic_istream, __stdinbuf, char, cin);
----------------
ldionne wrote:

Let's document the (pre-existing) fact that `cin` & friends are technically an ODR-violation because they are defined as `stream_data` but used as `std::istream` (as declared in `<iostream>`).

https://github.com/llvm/llvm-project/pull/124103