Re: [PATCH, libstdc++] GLIBCXX_HAVE_INT64_T

[Jonathan Wakely <jwakely@redhat.com>]

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On 06/01/21 19:41 -0500, David Edelsohn wrote:
>Thanks for clarifying the issue.
>
>As you implicitly point out, GCC knows the type of INT64 and defines
>the macro __INT64_TYPE__ .  The revised code can use that directly,
>such as:
>
>#if defined(_GLIBCXX_HAVE_INT64_T_LONG) \
>    || defined(_GLIBCXX_HAVE_INT64_T_LONG_LONG)
>   typedef __INT64_TYPE__   streamoff;
> #elif defined(_GLIBCXX_HAVE_INT64_T)
>   typedef int64_t                     streamoff;
> #else
>   typedef long long                 streamoff;
> #endif
>
>Are there any additional issues not addressed by that approach, other
>than possible further simplification?

That avoids the ABI break that Jakub pointed out. But I think we can
simplify it further, as in the attached patch.

This uses __INT64_TYPE__ if that's defined, and long long otherwise. I
think that should be equivalent in all practical cases (I can imagine
some strange target where __INT64_TYPE__ is defined by the compiler,
but int64_t isn't defined when the configure checks look for it, and
so the current code would use long long and with my patch would use
__INT64_TYPE__ which could be long ... but I think in practice that's
unlikely. It was probably more likely in older releases where the
configure test would have been done with -std=gnu++98 and so int64_t
might not have been declared by libc's <stdint.h>, but if that was the
case then any ABI break it caused happened years ago.




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diff --git a/libstdc++-v3/acinclude.m4 b/libstdc++-v3/acinclude.m4
index e4175ea3e64..f13c5d2467f 100644
--- a/libstdc++-v3/acinclude.m4
+++ b/libstdc++-v3/acinclude.m4
@@ -474,63 +474,6 @@ AC_DEFUN([GLIBCXX_CHECK_WRITEV], [
 ])
 
 
-dnl
-dnl Check whether int64_t is available in <stdint.h>, and define HAVE_INT64_T.
-dnl Also check whether int64_t is actually a typedef to long or long long.
-dnl
-AC_DEFUN([GLIBCXX_CHECK_INT64_T], [
-
-  AC_LANG_SAVE
-  AC_LANG_CPLUSPLUS
-
-  AC_MSG_CHECKING([for int64_t])
-  AC_CACHE_VAL(glibcxx_cv_INT64_T, [
-    AC_TRY_COMPILE(
-      [#include <stdint.h>],
-      [int64_t var;],
-      [glibcxx_cv_INT64_T=yes],
-      [glibcxx_cv_INT64_T=no])
-  ])
-
-  if test $glibcxx_cv_INT64_T = yes; then
-    AC_DEFINE(HAVE_INT64_T, 1, [Define if int64_t is available in <stdint.h>.])
-    AC_MSG_RESULT($glibcxx_cv_INT64_T)
-
-    AC_MSG_CHECKING([for int64_t as long])
-    AC_CACHE_VAL(glibcxx_cv_int64_t_long, [
-      AC_TRY_COMPILE(
-	[#include <stdint.h>
-	template<typename, typename> struct same { enum { value = -1 }; };
-	template<typename Tp> struct same<Tp, Tp> { enum { value = 1 }; };
-	int array[same<int64_t, long>::value];], [],
-	[glibcxx_cv_int64_t_long=yes], [glibcxx_cv_int64_t_long=no])
-    ])
-
-    if test $glibcxx_cv_int64_t_long = yes; then
-      AC_DEFINE(HAVE_INT64_T_LONG, 1, [Define if int64_t is a long.])
-      AC_MSG_RESULT($glibcxx_cv_int64_t_long)
-    fi
-
-    AC_MSG_CHECKING([for int64_t as long long])
-    AC_CACHE_VAL(glibcxx_cv_int64_t_long_long, [
-      AC_TRY_COMPILE(
-	[#include <stdint.h>
-	template<typename, typename> struct same { enum { value = -1 }; };
-	template<typename Tp> struct same<Tp, Tp> { enum { value = 1 }; };
-	int array[same<int64_t, long long>::value];], [],
-	[glibcxx_cv_int64_t_long_long=yes], [glibcxx_cv_int64_t_long_long=no])
-    ])
-
-    if test $glibcxx_cv_int64_t_long_long = yes; then
-      AC_DEFINE(HAVE_INT64_T_LONG_LONG, 1, [Define if int64_t is a long long.])
-      AC_MSG_RESULT($glibcxx_cv_int64_t_long_long)
-    fi
-  fi
-
-  AC_LANG_RESTORE
-])
-
-
 dnl
 dnl Check whether LFS support is available.
 dnl
diff --git a/libstdc++-v3/configure.ac b/libstdc++-v3/configure.ac
index 3c799be82b1..a816ff79d16 100644
--- a/libstdc++-v3/configure.ac
+++ b/libstdc++-v3/configure.ac
@@ -185,9 +185,6 @@ GLIBCXX_CHECK_STDIO_PROTO
 GLIBCXX_CHECK_MATH11_PROTO
 GLIBCXX_CHECK_UCHAR_H
 
-# For the streamoff typedef.
-GLIBCXX_CHECK_INT64_T
-
 # For LFS support.
 GLIBCXX_CHECK_LFS
 
diff --git a/libstdc++-v3/include/bits/postypes.h b/libstdc++-v3/include/bits/postypes.h
index 718ff44628c..d2fbfc35dee 100644
--- a/libstdc++-v3/include/bits/postypes.h
+++ b/libstdc++-v3/include/bits/postypes.h
@@ -39,32 +39,6 @@
 
 #include <cwchar> // For mbstate_t
 
-// XXX If <stdint.h> is really needed, make sure to define the macros
-// before including it, in order not to break <tr1/cstdint> (and <cstdint>
-// in C++11).  Reconsider all this as soon as possible...
-#if (defined(_GLIBCXX_HAVE_INT64_T) && !defined(_GLIBCXX_HAVE_INT64_T_LONG) \
-     && !defined(_GLIBCXX_HAVE_INT64_T_LONG_LONG))
-
-#ifndef __STDC_LIMIT_MACROS
-# define _UNDEF__STDC_LIMIT_MACROS
-# define __STDC_LIMIT_MACROS
-#endif
-#ifndef __STDC_CONSTANT_MACROS
-# define _UNDEF__STDC_CONSTANT_MACROS
-# define __STDC_CONSTANT_MACROS
-#endif
-#include <stdint.h> // For int64_t
-#ifdef _UNDEF__STDC_LIMIT_MACROS
-# undef __STDC_LIMIT_MACROS
-# undef _UNDEF__STDC_LIMIT_MACROS
-#endif
-#ifdef _UNDEF__STDC_CONSTANT_MACROS
-# undef __STDC_CONSTANT_MACROS
-# undef _UNDEF__STDC_CONSTANT_MACROS
-#endif
-
-#endif
-
 namespace std _GLIBCXX_VISIBILITY(default)
 {
 _GLIBCXX_BEGIN_NAMESPACE_VERSION
@@ -84,12 +58,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
    *  Note: In versions of GCC up to and including GCC 3.3, streamoff
    *  was typedef long.
   */  
-#ifdef _GLIBCXX_HAVE_INT64_T_LONG
-  typedef long          streamoff;
-#elif defined(_GLIBCXX_HAVE_INT64_T_LONG_LONG)
-  typedef long long     streamoff;
-#elif defined(_GLIBCXX_HAVE_INT64_T) 
-  typedef int64_t       streamoff;
+#ifdef __INT64_TYPE__
+  typedef __INT64_TYPE__          streamoff;
 #else
   typedef long long     streamoff;
 #endif