[gcc r12-6097] Fortran: allow __float128 on targets where long double is not REAL(KIND=10)

["Franथईois-Xavier Coudert" <fxcoudert@gcc.gnu.org>]

https://gcc.gnu.org/g:228173565eafbe34e44c1600c32e32a323eb5aab

commit r12-6097-g228173565eafbe34e44c1600c32e32a323eb5aab
Author: Francois-Xavier Coudert <fxcoudert@gmail.com>
Date:   Wed Dec 22 12:46:07 2021 +0100

    Fortran: allow __float128 on targets where long double is not REAL(KIND=10)
    
    The logic for detection of REAL(KIND=16) in kinds-override.h made
    assumptions:
    
        -- if real(kind=10) exists, i.e. if HAVE_GFC_REAL_10 is defined,
           then it is necessarily the "long double" type
        -- if real(kind=16) exists, then:
           * if HAVE_GFC_REAL_10, real(kind=16) is "__float128"
           * otherwise, real(kind=16) is "long double"
    
    This may not always be true. Take the aarch64-apple-darwin port,
    it has double == long double == binary64, and __float128 == binary128.
    
    We already have more fine-grained logic in the mk-kinds-h.sh script,
    where we actually check the Fortran kind corresponding to C’s long
    double. So let's use it, and emit the GFC_REAL_16_IS_FLOAT128 /
    GFC_REAL_16_IS_LONG_DOUBLE macros there.
    
    libgfortran/ChangeLog:
    
            * kinds-override.h: Move GFC_REAL_16_IS_* macros...
            * mk-kinds-h.sh: ... here.

Diff:
---
 libgfortran/kinds-override.h | 23 ++++-------------------
 libgfortran/mk-kinds-h.sh    |  6 +++++-
 2 files changed, 9 insertions(+), 20 deletions(-)

diff --git a/libgfortran/kinds-override.h b/libgfortran/kinds-override.h
index c9e874a3f38..5f7840b0c89 100644
--- a/libgfortran/kinds-override.h
+++ b/libgfortran/kinds-override.h
@@ -23,24 +23,9 @@ see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
 <http://www.gnu.org/licenses/>.  */
 
 
-/* What are the C types corresponding to the real(kind=10) and
-   real(kind=16) types? We currently rely on the following assumptions:
-     -- if real(kind=10) exists, i.e. if HAVE_GFC_REAL_10 is defined,
-        then it is necessarily the "long double" type
-     -- if real(kind=16) exists, then:
-         * if HAVE_GFC_REAL_10, real(kind=16) is "__float128"
-	 * otherwise, real(kind=16) is "long double"
-   To allow to change this in the future, we create the
-   GFC_REAL_16_IS_FLOAT128 macro that is used throughout libgfortran.  */
-
-#if defined(HAVE_GFC_REAL_16)
-# if defined(HAVE_GFC_REAL_10)
-#  define GFC_REAL_16_IS_FLOAT128
-#  if !defined(HAVE_FLOAT128)
-#   error "Where has __float128 gone?"
-#  endif
-# else
-#  define GFC_REAL_16_IS_LONG_DOUBLE
-# endif
+/* Ensure that TFmode is available under.  */
+
+#if defined(GFC_REAL_16_IS_FLOAT128) && !defined(HAVE_FLOAT128)
+# error "Where has __float128 gone?"
 #endif
 
diff --git a/libgfortran/mk-kinds-h.sh b/libgfortran/mk-kinds-h.sh
index 249619061c6..572878ce891 100755
--- a/libgfortran/mk-kinds-h.sh
+++ b/libgfortran/mk-kinds-h.sh
@@ -64,15 +64,19 @@ for k in $possible_real_kinds; do
     case $k in
       4) ctype="float" ; cplxtype="complex float" ; suffix="f" ;;
       8) ctype="double" ; cplxtype="complex double" ; suffix="" ;;
+      # If we have a REAL(KIND=10), it is always long double
       10) ctype="long double" ; cplxtype="complex long double" ; suffix="l" ;;
-      16) if [ $long_double_kind -eq 10 ]; then
+      # If we have a REAL(KIND=16), it is either long double or __float128
+      16) if [ $long_double_kind -ne 16 ]; then
 	    ctype="__float128"
 	    cplxtype="_Complex float __attribute__((mode(TC)))"
 	    suffix="q"
+	    echo "#define GFC_REAL_16_IS_FLOAT128"
 	  else
 	    ctype="long double"
 	    cplxtype="complex long double"
 	    suffix="l"
+	    echo "#define GFC_REAL_16_IS_LONG_DOUBLE"
 	  fi ;;
       *) echo "$0: Unknown type" >&2 ; exit 1 ;;
     esac