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AC_CHECK_FUNC not safe WRT link time optimizing compilers

From: Jan Hubicka
Subject: AC_CHECK_FUNC not safe WRT link time optimizing compilers
Date: Mon, 25 Oct 2010 20:39:07 +0200
User-agent: Mutt/1.5.18 (2008-05-17)

AC_CHECK_FUNC produce test like the following:
char pstat_getstatic ();
char (*f) () = pstat_getstatic;
main ()
  return f != pstat_getstatic;

New GCC with link time optimization is smart enough to ask the linker plugin 
and work out that
variable F is used only by the LTO code.  This makes GCC to promote F as read 
only variable
since it is never written and the test to be optimized away.

Would be possible to fix this, for example, by converting it to:
int pstat_getstatic ();
main ()
  return pstat_getstatic ();

or by marking F volatile?
See http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46055
this prevents me from making GCC to use linker plugin information correctly.


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