gcc/testsuite/gcc.dg/attr-flatten-1.c

/* { dg-require-alias "" } */
int fn2(int);
int fn3(int);

__attribute__((flatten))
int fn1(int p1)
{
  int a = fn2(p1);
  return fn3(a);
}
__attribute__((flatten))
__attribute__((alias("fn1")))
int fn4(int p1);

/* Again, but this time the target doesn't have the attribute.  */
int fn1a(int p1)
{
  int a = fn2(p1);
  return fn3(a);
}
__attribute__((flatten))
__attribute__((alias("fn1a")))
int fn4a(int p1); /* { dg-warning "ignored" } */

int
test ()
{
  return fn4(1)+fn4a(1);
}