gcc/testsuite/gcc.dg/c11-floatn-4.c

/* { dg-do compile } */
/* { dg-options "-std=c11 -pedantic-errors" } */
/* { dg-add-options float64x } */
/* { dg-require-effective-target float64x } */

_Float64x a		/* { dg-error "ISO C does not support the '_Float64x' type before C23" } */
  = 1.0F64x;		/* { dg-error "non-standard suffix on floating constant before C23" } */
__extension__ _Float64x b
  = 2.0F64x;