Fortran: F2018 rounding modes changes

Add the new IEEE_AWAY rounding mode. It is unsupported on all known
targets, but could be supported by glibc and AIX as part of the C2x
proposal. Testing for now is minimal.

Add the optional RADIX argument to IEEE_SET_ROUNDING_MODE and
IEEE_GET_ROUNDING_MODE. It is unused for now, because we do not
support radices other than 2.

2022-08-31  Francois-Xavier Coudert <fxcoudert@gcc.gnu.org>

gcc/fortran/
	* libgfortran.h: Declare GFC_FPE_AWAY.

gcc/testsuite/
	* gfortran.dg/ieee/rounding_2.f90: New test.

libgfortran/
	* ieee/ieee_arithmetic.F90: Add RADIX argument to
	IEEE_SET_ROUNDING_MODE and IEEE_GET_ROUNDING_MODE.
	* config/fpu-387.h: Add IEEE_AWAY mode.
	* config/fpu-aarch64.h: Add IEEE_AWAY mode.
	* config/fpu-aix.h: Add IEEE_AWAY mode.
	* config/fpu-generic.h: Add IEEE_AWAY mode.
	* config/fpu-glibc.h: Add IEEE_AWAY mode.
	* config/fpu-sysv.h: Add IEEE_AWAY mode.

9 files changed, 88 insertions, 12 deletions

diff --git a/gcc/fortran/libgfortran.h b/gcc/fortran/libgfortran.h
index ef06194..79a8c2f 100644
--- a/gcc/fortran/libgfortran.h
+++ b/gcc/fortran/libgfortran.h
@@ -60,6 +60,7 @@ along with GCC; see the file COPYING3.  If not see
 #define GFC_FPE_TONEAREST  2
 #define GFC_FPE_TOWARDZERO 3
 #define GFC_FPE_UPWARD     4
+#define GFC_FPE_AWAY       5
 
 /* Size of the buffer required to store FPU state for any target.
    In particular, this has to be larger than fenv_t on all glibc targets.
diff --git a/gcc/testsuite/gfortran.dg/ieee/rounding_2.f90 b/gcc/testsuite/gfortran.dg/ieee/rounding_2.f90
new file mode 100644
index 0000000..8af6c91
--- /dev/null
+++ b/gcc/testsuite/gfortran.dg/ieee/rounding_2.f90
@@ -0,0 +1,20 @@
+! { dg-do run }
+
+  use, intrinsic :: ieee_arithmetic
+  implicit none
+
+  real :: sx1, sx2, sx3
+  double precision :: dx1, dx2, dx3
+
+  ! IEEE_AWAY was added in Fortran 2018 and not supported by any target
+  ! at the moment. Just check we can query for its support.
+
+  ! We should support at least C float and C double types
+  if (ieee_support_rounding(ieee_away) &
+      .or. ieee_support_rounding(ieee_away, 0.) &
+      .or. ieee_support_rounding(ieee_away, 0.d0)) then
+    print *, "If a target / libc now supports this, we need to add a proper check!"
+    stop 1
+  end if
+
+end
diff --git a/libgfortran/config/fpu-387.h b/libgfortran/config/fpu-387.h
index fd00dab..e2f4a7d 100644
--- a/libgfortran/config/fpu-387.h
+++ b/libgfortran/config/fpu-387.h
@@ -418,9 +418,12 @@ get_fpu_rounding_mode (void)
 }
 
 int
-support_fpu_rounding_mode (int mode __attribute__((unused)))
+support_fpu_rounding_mode (int mode)
 {
-  return 1;
+  if (mode == GFC_FPE_AWAY)
+    return 0;
+  else
+    return 1;
 }
 
 void
diff --git a/libgfortran/config/fpu-aarch64.h b/libgfortran/config/fpu-aarch64.h
index 3a2e4ba..4789390 100644
--- a/libgfortran/config/fpu-aarch64.h
+++ b/libgfortran/config/fpu-aarch64.h
@@ -293,9 +293,12 @@ set_fpu_rounding_mode (int round)
 
 
 int
-support_fpu_rounding_mode (int mode __attribute__((unused)))
+support_fpu_rounding_mode (int mode)
 {
-  return 1;
+  if (mode == GFC_FPE_AWAY)
+    return 0;
+  else
+    return 1;
 }
 
 
diff --git a/libgfortran/config/fpu-aix.h b/libgfortran/config/fpu-aix.h
index c643874..fb1ac80 100644
--- a/libgfortran/config/fpu-aix.h
+++ b/libgfortran/config/fpu-aix.h
@@ -320,6 +320,11 @@ get_fpu_rounding_mode (void)
 	return GFC_FPE_TOWARDZERO;
 #endif
 
+#ifdef FE_TONEARESTFROMZERO
+      case FE_TONEARESTFROMZERO:
+	return GFC_FPE_AWAY;
+#endif
+
       default:
 	return 0; /* Should be unreachable.  */
     }
@@ -357,8 +362,14 @@ set_fpu_rounding_mode (int mode)
 	break;
 #endif
 
+#ifdef FE_TONEARESTFROMZERO
+      case GFC_FPE_AWAY:
+	rnd_mode = FE_TONEARESTFROMZERO;
+	break;
+#endif
+
       default:
-	return; /* Should be unreachable.  */
+	return;
     }
 
   fesetround (rnd_mode);
@@ -398,8 +409,15 @@ support_fpu_rounding_mode (int mode)
 	return 0;
 #endif
 
+      case GFC_FPE_AWAY:
+#ifdef FE_TONEARESTFROMZERO
+	return 1;
+#else
+	return 0;
+#endif
+
       default:
-	return 0; /* Should be unreachable.  */
+	return 0;
     }
 }
 
diff --git a/libgfortran/config/fpu-generic.h b/libgfortran/config/fpu-generic.h
index 3b62228..9e976a8 100644
--- a/libgfortran/config/fpu-generic.h
+++ b/libgfortran/config/fpu-generic.h
@@ -66,9 +66,16 @@ get_fpu_except_flags (void)
 
 int
 get_fpu_rounding_mode (void)
-{   
+{
+  return 0;
+}
+
+
+int
+support_fpu_rounding_mode (int mode __attribute__((unused)))
+{
   return 0;
-}               
+}
 
 
 void
diff --git a/libgfortran/config/fpu-glibc.h b/libgfortran/config/fpu-glibc.h
index 265ef69..f34b696 100644
--- a/libgfortran/config/fpu-glibc.h
+++ b/libgfortran/config/fpu-glibc.h
@@ -342,6 +342,11 @@ get_fpu_rounding_mode (void)
 	return GFC_FPE_TOWARDZERO;
 #endif
 
+#ifdef FE_TONEARESTFROMZERO
+      case FE_TONEARESTFROMZERO:
+	return GFC_FPE_AWAY;
+#endif
+
       default:
 	return 0; /* Should be unreachable.  */
     }
@@ -379,6 +384,12 @@ set_fpu_rounding_mode (int mode)
 	break;
 #endif
 
+#ifdef FE_TONEARESTFROMZERO
+      case GFC_FPE_AWAY:
+	rnd_mode = FE_TONEARESTFROMZERO;
+	break;
+#endif
+
       default:
 	return; /* Should be unreachable.  */
     }
@@ -420,6 +431,13 @@ support_fpu_rounding_mode (int mode)
 	return 0;
 #endif
 
+      case GFC_FPE_AWAY:
+#ifdef FE_TONEARESTFROMZERO
+	return 1;
+#else
+	return 0;
+#endif
+
       default:
 	return 0; /* Should be unreachable.  */
     }
diff --git a/libgfortran/config/fpu-sysv.h b/libgfortran/config/fpu-sysv.h
index 4de3852..4681322 100644
--- a/libgfortran/config/fpu-sysv.h
+++ b/libgfortran/config/fpu-sysv.h
@@ -374,9 +374,12 @@ set_fpu_rounding_mode (int mode)
 
 
 int
-support_fpu_rounding_mode (int mode __attribute__((unused)))
+support_fpu_rounding_mode (int mode)
 {
-  return 1;
+  if (mode == GFC_FPE_AWAY)
+    return 0;
+  else
+    return 1;
 }
 
 
diff --git a/libgfortran/ieee/ieee_arithmetic.F90 b/libgfortran/ieee/ieee_arithmetic.F90
index 4e01aa5..7dce37a 100644
--- a/libgfortran/ieee/ieee_arithmetic.F90
+++ b/libgfortran/ieee/ieee_arithmetic.F90
@@ -73,6 +73,7 @@ module IEEE_ARITHMETIC
     IEEE_TO_ZERO           = IEEE_ROUND_TYPE(GFC_FPE_TOWARDZERO), &
     IEEE_UP                = IEEE_ROUND_TYPE(GFC_FPE_UPWARD), &
     IEEE_DOWN              = IEEE_ROUND_TYPE(GFC_FPE_DOWNWARD), &
+    IEEE_AWAY              = IEEE_ROUND_TYPE(GFC_FPE_AWAY), &
     IEEE_OTHER             = IEEE_ROUND_TYPE(0)
 
 
@@ -1044,9 +1045,10 @@ contains
 
   ! IEEE_GET_ROUNDING_MODE
 
-  subroutine IEEE_GET_ROUNDING_MODE (ROUND_VALUE)
+  subroutine IEEE_GET_ROUNDING_MODE (ROUND_VALUE, RADIX)
     implicit none
     type(IEEE_ROUND_TYPE), intent(out) :: ROUND_VALUE
+    integer, intent(in), optional :: RADIX
 
     interface
       integer function helper() &
@@ -1060,9 +1062,10 @@ contains
 
   ! IEEE_SET_ROUNDING_MODE
 
-  subroutine IEEE_SET_ROUNDING_MODE (ROUND_VALUE)
+  subroutine IEEE_SET_ROUNDING_MODE (ROUND_VALUE, RADIX)
     implicit none
     type(IEEE_ROUND_TYPE), intent(in) :: ROUND_VALUE
+    integer, intent(in), optional :: RADIX
 
     interface
       subroutine helper(val) &