Check if __assume is supported

Merged: https://github.com/ruby/ruby/pull/5577

configure.ac

@@ -1679,6 +1679,18 @@ AS_IF([test "$GCC" = yes], [
     AS_IF([test "$rb_cv_func___builtin_unreachable" = yes], [
 	AC_DEFINE(HAVE___BUILTIN_UNREACHABLE)
     ])
+
+    AC_CACHE_CHECK(for __assume, rb_cv_func___assume,
+    [RUBY_WERROR_FLAG([
+        AC_LINK_IFELSE([AC_LANG_PROGRAM([[]],
+            [[__assume(1);]])],
+            [rb_cv_func___assume=yes],
+            [rb_cv_func___assume=no])
+    ])
+    ])
+    AS_IF([test "$rb_cv_func___assume" = yes], [
+	AC_DEFINE(HAVE___ASSUME)
+    ])
 }
 
 AC_CACHE_CHECK(for exported function attribute, rb_cv_func_exported, [

include/ruby/backward/2/assume.h

@@ -24,7 +24,6 @@
 #include "ruby/internal/assume.h"
 #include "ruby/internal/has/builtin.h"
 
-#undef  ASSUME             /* Kill config.h definition */
 #define ASSUME             RBIMPL_ASSUME             /**< @old{RBIMPL_ASSUME} */
 #define UNREACHABLE        RBIMPL_UNREACHABLE()      /**< @old{RBIMPL_UNREACHABLE} */
 #define UNREACHABLE_RETURN RBIMPL_UNREACHABLE_RETURN /**< @old{RBIMPL_UNREACHABLE_RETURN} */

include/ruby/internal/assume.h

@@ -32,10 +32,7 @@
 #include "ruby/internal/warning_push.h"
 
 /** @cond INTERNAL_MACRO */
-#if RBIMPL_COMPILER_SINCE(MSVC, 13, 10, 0)
-# define RBIMPL_HAVE___ASSUME
-
-#elif RBIMPL_COMPILER_SINCE(Intel, 13, 0, 0)
+#if defined(HAVE___ASSUME)
 # define RBIMPL_HAVE___ASSUME
 #endif
 /** @endcond */

win32/Makefile.sub

@@ -702,7 +702,7 @@ $(CONFIG_H): $(MKFILES) $(srcdir)/win32/Makefile.sub $(win_srcdir)/Makefile.sub
 #define ALWAYS_INLINE(x) __forceinline x
 #define WARN_UNUSED_RESULT(x) x
 #define MAYBE_UNUSED(x) x
-#define ASSUME(x) __assume(!!(x))
+#define HAVE___ASSUME 1
 #define FUNC_STDCALL(x) __stdcall x
 #define FUNC_CDECL(x) __cdecl x
 #define FUNC_FASTCALL(x) __fastcall x