Fortran: Use _Float128 rather than __float128 for c_float128 kind.

The GNU Fortran manual documents that the c_float128 kind corresponds
to __float128, but in fact the implementation uses float128_type_node,
which is _Float128.  Both refer to the 128-bit IEEE/ISO encoding, but
some targets including aarch64 only define _Float128 and not __float128,
and do not provide quadmath.h.  This caused errors in some test cases
referring to __float128.

This patch changes the documentation (including code comments) and
test cases to use _Float128 to match the implementation.

2021-09-16  Sandra Loosemore  <sandra@codesourcery.com>

gcc/fortran/

	* intrinsic.texi (ISO_C_BINDING): Change C_FLOAT128 to correspond
	to _Float128 rather than __float128.
	* iso-c-binding.def (c_float128): Update comments.
	* trans-intrinsic.c (gfc_builtin_decl_for_float_kind): Likewise.
	(build_round_expr): Likewise.
	(gfc_build_intrinsic_lib_fndcecls): Likewise.
	* trans-types.h (gfc_real16_is_float128): Likewise.

gcc/testsuite/
	* gfortran.dg/PR100914.c: Do not include quadmath.h.  Use
	_Float128 _Complex instead of __complex128.
	* gfortran.dg/PR100914.f90: Add -Wno-pedantic to suppress error
	about use of _Float128.
	* gfortran.dg/c-interop/typecodes-array-float128-c.c: Use
	_Float128 instead of __float128.
	* gfortran.dg/c-interop/typecodes-sanity-c.c: Likewise.
	* gfortran.dg/c-interop/typecodes-scalar-float128-c.c: Likewise.
	* lib/target-supports.exp
	(check_effective_target_fortran_real_c_float128): Update comments.

libgfortran/
	* ISO_Fortran_binding.h: Update comments.
	* runtime/ISO_Fortran_binding.c: Likewise.

2 files changed, 3 insertions, 3 deletions

diff --git a/libgfortran/ISO_Fortran_binding.h b/libgfortran/ISO_Fortran_binding.h
index 50b02d2..d431d09 100644
--- a/libgfortran/ISO_Fortran_binding.h
+++ b/libgfortran/ISO_Fortran_binding.h
@@ -281,7 +281,7 @@ extern int CFI_setpointer (CFI_cdesc_t *, CFI_cdesc_t *, const CFI_index_t []);
 #define CFI_type_long_double (CFI_type_Real + (10 << CFI_type_kind_shift))
 #define CFI_type_long_double_Complex (CFI_type_Complex + (10 << CFI_type_kind_shift))
 
-/* This is the IEEE 128-bit encoding, same as float128.  */
+/* This is the IEEE 128-bit encoding, same as _Float128.  */
 #elif (__CFI_LDBL_MANT_DIG__ == 113 \
        && __CFI_LDBL_MIN_EXP__ == -16381 \
        && __CFI_LDBL_MAX_EXP__ == 16384)
@@ -303,7 +303,7 @@ extern int CFI_setpointer (CFI_cdesc_t *, CFI_cdesc_t *, const CFI_index_t []);
 #error "Can't determine kind of long double"
 #endif
 
-/* Similarly for __float128.  This always refers to the IEEE encoding
+/* Similarly for _Float128.  This always refers to the IEEE encoding
    and not some other 128-bit representation, so if we already used
    kind 16 for a non-IEEE representation, this one must be unsupported
    in Fortran even if it's available in C.  */
diff --git a/libgfortran/runtime/ISO_Fortran_binding.c b/libgfortran/runtime/ISO_Fortran_binding.c
index 0e1a419..e01cc65 100644
--- a/libgfortran/runtime/ISO_Fortran_binding.c
+++ b/libgfortran/runtime/ISO_Fortran_binding.c
@@ -222,7 +222,7 @@ gfc_desc_to_cfi_desc (CFI_cdesc_t **d_ptr, const gfc_array_void *s)
      elem_len and not the kind, we get into trouble with long double kinds
      that do not correspond directly to the elem_len, specifically the
      kind 10 80-bit long double on x86 targets.  On x86_64, this has size
-     16 and cannot be differentiated from true __float128.  Prefer the
+     16 and cannot be differentiated from true _Float128.  Prefer the
      standard long double type over the GNU extension in that case.  */
   if (d->type == CFI_type_Real && kind == sizeof (long double))
     d->type = CFI_type_long_double;