# AC_CHECK_FASTCALL([if-ok],[if-notok])

 # Test if the compiler recognizes __attribute__((regparm(3))) - we don't 

 # currently check if it actually works correctly, but probably should...

 # -----------------------

 AC_DEFUN([AC_CHECK_FASTCALL], [

 AC_MSG_CHECKING([support for fastcall calling conventions]);

 AC_RUN_IFELSE([

   AC_LANG_SOURCE([[

 int __attribute__((regparm(3))) foo(int a, int b) { return a+b; }

 int main(int argc, char *argv[])

 {

    return foo( 1, 2 ) == 3 ? 0 : 1;

 }]])], [ 

    AC_MSG_RESULT([yes])

    $1 ], [ 

    AC_MSG_RESULT([no])

    $2 ])

 ])

 # AC_CHECK_FRAME_ADDRESS([if-ok],[if-notok])

 # Test if the compiler will let us modify the return address on the stack

 # via __builtin_frame_address()

 # -----------------------

 AC_DEFUN([AC_CHECK_FRAME_ADDRESS], [

 AC_MSG_CHECKING([if we have a working __builtin_frame_address()]);

 AC_RUN_IFELSE([

   AC_LANG_SOURCE([[

 void * __attribute__((noinline)) first_arg( void *x, void *y ) { return x; }

 int __attribute__((noinline)) foo( int arg, void *exc )

 {

     if( arg < 2 ) {

         *(((void **)__builtin_frame_address(0))+1) = exc;

     }

     return 0;

 }

 int main(int argc, char *argv[])

 {

    goto *first_arg(&&start, &&except);

 start:

    return foo( argc, &&except ) + 1;

 except:

    return 0;

 }]])], [ 

    AC_MSG_RESULT([yes])

    $1 ], [ 

    AC_MSG_RESULT([no])

    $2 ])

 ])