Index: gcc/target.def
===================================================================
--- gcc/target.def	2017-07-05 16:29:19.600761904 +0100
+++ gcc/target.def	2017-07-13 09:18:26.916877727 +0100
@@ -3374,20 +3374,20 @@ DEFHOOK
 (floatn_mode,
  "Define this to return the machine mode to use for the type \n\
 @code{_Float@var{n}}, if @var{extended} is false, or the type \n\
-@code{_Float@var{n}x}, if @var{extended} is true.  If such a type \n\
-is not supported, return @code{VOIDmode}.  The default version of this \n\
-hook returns @code{SFmode} for @code{_Float32}, @code{DFmode} for \n\
+@code{_Float@var{n}x}, if @var{extended} is true.  If such a type is not\n\
+supported, return @code{opt_scalar_float_mode ()}.  The default version of\n\
+this hook returns @code{SFmode} for @code{_Float32}, @code{DFmode} for\n\
 @code{_Float64} and @code{_Float32x} and @code{TFmode} for \n\
 @code{_Float128}, if those modes exist and satisfy the requirements for \n\
 those types and pass @code{TARGET_SCALAR_MODE_SUPPORTED_P} and \n\
 @code{TARGET_LIBGCC_FLOATING_MODE_SUPPORTED_P}; for @code{_Float64x}, it \n\
 returns the first of @code{XFmode} and @code{TFmode} that exists and \n\
 satisfies the same requirements; for other types, it returns \n\
-@code{VOIDmode}.  The hook is only called for values of @var{n} and \n\
-@var{extended} that are valid according to ISO/IEC TS 18661-3:2015; that \n\
-is, @var{n} is one of 32, 64, 128, or, if @var{extended} is false, 16 or \n\
-greater than 128 and a multiple of 32.",
- machine_mode, (int n, bool extended),
+@code{opt_scalar_float_mode ()}.  The hook is only called for values\n\
+of @var{n} and @var{extended} that are valid according to\n\
+ISO/IEC TS 18661-3:2015; that is, @var{n} is one of 32, 64, 128, or,\n\
+if @var{extended} is false, 16 or greater than 128 and a multiple of 32.",
+ opt_scalar_float_mode, (int n, bool extended),
  default_floatn_mode)
 
 /* Compute cost of moving data from a register of class FROM to one of
Index: gcc/doc/tm.texi
===================================================================
--- gcc/doc/tm.texi	2017-07-05 16:29:19.597161905 +0100
+++ gcc/doc/tm.texi	2017-07-13 09:18:26.914877921 +0100
@@ -4267,22 +4267,22 @@ hook returns true for all of @code{SFmod
 @code{XFmode} and @code{TFmode}, if such modes exist.
 @end deftypefn
 
-@deftypefn {Target Hook} machine_mode TARGET_FLOATN_MODE (int @var{n}, bool @var{extended})
+@deftypefn {Target Hook} opt_scalar_float_mode TARGET_FLOATN_MODE (int @var{n}, bool @var{extended})
 Define this to return the machine mode to use for the type 
 @code{_Float@var{n}}, if @var{extended} is false, or the type 
-@code{_Float@var{n}x}, if @var{extended} is true.  If such a type 
-is not supported, return @code{VOIDmode}.  The default version of this 
-hook returns @code{SFmode} for @code{_Float32}, @code{DFmode} for 
+@code{_Float@var{n}x}, if @var{extended} is true.  If such a type is not
+supported, return @code{opt_scalar_float_mode ()}.  The default version of
+this hook returns @code{SFmode} for @code{_Float32}, @code{DFmode} for
 @code{_Float64} and @code{_Float32x} and @code{TFmode} for 
 @code{_Float128}, if those modes exist and satisfy the requirements for 
 those types and pass @code{TARGET_SCALAR_MODE_SUPPORTED_P} and 
 @code{TARGET_LIBGCC_FLOATING_MODE_SUPPORTED_P}; for @code{_Float64x}, it 
 returns the first of @code{XFmode} and @code{TFmode} that exists and 
 satisfies the same requirements; for other types, it returns 
-@code{VOIDmode}.  The hook is only called for values of @var{n} and 
-@var{extended} that are valid according to ISO/IEC TS 18661-3:2015; that 
-is, @var{n} is one of 32, 64, 128, or, if @var{extended} is false, 16 or 
-greater than 128 and a multiple of 32.
+@code{opt_scalar_float_mode ()}.  The hook is only called for values
+of @var{n} and @var{extended} that are valid according to
+ISO/IEC TS 18661-3:2015; that is, @var{n} is one of 32, 64, 128, or,
+if @var{extended} is false, 16 or greater than 128 and a multiple of 32.
 @end deftypefn
 
 @deftypefn {Target Hook} bool TARGET_SMALL_REGISTER_CLASSES_FOR_MODE_P (machine_mode @var{mode})
Index: gcc/config/arm/arm.c
===================================================================
--- gcc/config/arm/arm.c	2017-07-13 09:18:25.327032350 +0100
+++ gcc/config/arm/arm.c	2017-07-13 09:18:26.899879373 +0100
@@ -311,7 +311,7 @@ static bool arm_asm_elf_flags_numeric (u
 static unsigned int arm_elf_section_type_flags (tree decl, const char *name,
 						int reloc);
 static void arm_expand_divmod_libfunc (rtx, machine_mode, rtx, rtx, rtx *, rtx *);
-static machine_mode arm_floatn_mode (int, bool);
+static opt_scalar_float_mode arm_floatn_mode (int, bool);
 
 /* Table of machine attributes.  */
 static const struct attribute_spec arm_attribute_table[] =
@@ -23653,11 +23653,15 @@ arm_excess_precision (enum excess_precis
 /* Implement TARGET_FLOATN_MODE.  Make very sure that we don't provide
    _Float16 if we are using anything other than ieee format for 16-bit
    floating point.  Otherwise, punt to the default implementation.  */
-static machine_mode
+static opt_scalar_float_mode
 arm_floatn_mode (int n, bool extended)
 {
   if (!extended && n == 16)
-    return arm_fp16_format == ARM_FP16_FORMAT_IEEE ? HFmode : VOIDmode;
+    {
+      if (arm_fp16_format == ARM_FP16_FORMAT_IEEE)
+	return HFmode;
+      return opt_scalar_float_mode ();
+    }
 
   return default_floatn_mode (n, extended);
 }
Index: gcc/config/powerpcspe/powerpcspe.c
===================================================================
--- gcc/config/powerpcspe/powerpcspe.c	2017-07-13 09:18:19.102696197 +0100
+++ gcc/config/powerpcspe/powerpcspe.c	2017-07-13 09:18:26.902879083 +0100
@@ -39201,7 +39201,7 @@ rs6000_vector_mode_supported_p (machine_
 }
 
 /* Target hook for floatn_mode.  */
-static machine_mode
+static opt_scalar_float_mode
 rs6000_floatn_mode (int n, bool extended)
 {
   if (extended)
@@ -39215,10 +39215,10 @@ rs6000_floatn_mode (int n, bool extended
 	  if (TARGET_FLOAT128_KEYWORD)
 	    return (FLOAT128_IEEE_P (TFmode)) ? TFmode : KFmode;
 	  else
-	    return VOIDmode;
+	    return opt_scalar_float_mode ();
 
 	case 128:
-	  return VOIDmode;
+	  return opt_scalar_float_mode ();
 
 	default:
 	  /* Those are the only valid _FloatNx types.  */
@@ -39239,10 +39239,10 @@ rs6000_floatn_mode (int n, bool extended
 	  if (TARGET_FLOAT128_KEYWORD)
 	    return (FLOAT128_IEEE_P (TFmode)) ? TFmode : KFmode;
 	  else
-	    return VOIDmode;
+	    return opt_scalar_float_mode ();
 
 	default:
-	  return VOIDmode;
+	  return opt_scalar_float_mode ();
 	}
     }
 
Index: gcc/config/rs6000/rs6000.c
===================================================================
--- gcc/config/rs6000/rs6000.c	2017-07-13 09:18:19.117694534 +0100
+++ gcc/config/rs6000/rs6000.c	2017-07-13 09:18:26.909878405 +0100
@@ -36202,7 +36202,7 @@ rs6000_vector_mode_supported_p (machine_
 }
 
 /* Target hook for floatn_mode.  */
-static machine_mode
+static opt_scalar_float_mode
 rs6000_floatn_mode (int n, bool extended)
 {
   if (extended)
@@ -36216,10 +36216,10 @@ rs6000_floatn_mode (int n, bool extended
 	  if (TARGET_FLOAT128_KEYWORD)
 	    return (FLOAT128_IEEE_P (TFmode)) ? TFmode : KFmode;
 	  else
-	    return VOIDmode;
+	    return opt_scalar_float_mode ();
 
 	case 128:
-	  return VOIDmode;
+	  return opt_scalar_float_mode ();
 
 	default:
 	  /* Those are the only valid _FloatNx types.  */
@@ -36240,10 +36240,10 @@ rs6000_floatn_mode (int n, bool extended
 	  if (TARGET_FLOAT128_KEYWORD)
 	    return (FLOAT128_IEEE_P (TFmode)) ? TFmode : KFmode;
 	  else
-	    return VOIDmode;
+	    return opt_scalar_float_mode ();
 
 	default:
-	  return VOIDmode;
+	  return opt_scalar_float_mode ();
 	}
     }
 
Index: gcc/targhooks.h
===================================================================
--- gcc/targhooks.h	2017-07-05 16:29:19.601661904 +0100
+++ gcc/targhooks.h	2017-07-13 09:18:26.917877631 +0100
@@ -73,7 +73,7 @@ extern tree default_mangle_assembler_nam
 
 extern bool default_scalar_mode_supported_p (machine_mode);
 extern bool default_libgcc_floating_mode_supported_p (machine_mode);
-extern machine_mode default_floatn_mode (int, bool);
+extern opt_scalar_float_mode default_floatn_mode (int, bool);
 extern bool targhook_words_big_endian (void);
 extern bool targhook_float_words_big_endian (void);
 extern bool default_float_exceptions_rounding_supported_p (void);
Index: gcc/targhooks.c
===================================================================
--- gcc/targhooks.c	2017-07-13 09:18:19.145691430 +0100
+++ gcc/targhooks.c	2017-07-13 09:18:26.917877631 +0100
@@ -468,12 +468,12 @@ default_libgcc_floating_mode_supported_p
 /* Return the machine mode to use for the type _FloatN, if EXTENDED is
    false, or _FloatNx, if EXTENDED is true, or VOIDmode if not
    supported.  */
-machine_mode
+opt_scalar_float_mode
 default_floatn_mode (int n, bool extended)
 {
   if (extended)
     {
-      machine_mode cand1 = VOIDmode, cand2 = VOIDmode;
+      opt_scalar_float_mode cand1, cand2;
       switch (n)
 	{
 	case 32:
@@ -498,20 +498,20 @@ default_floatn_mode (int n, bool extende
 	  /* Those are the only valid _FloatNx types.  */
 	  gcc_unreachable ();
 	}
-      if (cand1 != VOIDmode
-	  && REAL_MODE_FORMAT (cand1)->ieee_bits > n
-	  && targetm.scalar_mode_supported_p (cand1)
-	  && targetm.libgcc_floating_mode_supported_p (cand1))
+      if (cand1.exists ()
+	  && REAL_MODE_FORMAT (*cand1)->ieee_bits > n
+	  && targetm.scalar_mode_supported_p (*cand1)
+	  && targetm.libgcc_floating_mode_supported_p (*cand1))
 	return cand1;
-      if (cand2 != VOIDmode
-	  && REAL_MODE_FORMAT (cand2)->ieee_bits > n
-	  && targetm.scalar_mode_supported_p (cand2)
-	  && targetm.libgcc_floating_mode_supported_p (cand2))
+      if (cand2.exists ()
+	  && REAL_MODE_FORMAT (*cand2)->ieee_bits > n
+	  && targetm.scalar_mode_supported_p (*cand2)
+	  && targetm.libgcc_floating_mode_supported_p (*cand2))
 	return cand2;
     }
   else
     {
-      machine_mode cand = VOIDmode;
+      opt_scalar_float_mode cand;
       switch (n)
 	{
 	case 16:
@@ -544,13 +544,13 @@ default_floatn_mode (int n, bool extende
 	default:
 	  break;
 	}
-      if (cand != VOIDmode
-	  && REAL_MODE_FORMAT (cand)->ieee_bits == n
-	  && targetm.scalar_mode_supported_p (cand)
-	  && targetm.libgcc_floating_mode_supported_p (cand))
+      if (cand.exists ()
+	  && REAL_MODE_FORMAT (*cand)->ieee_bits == n
+	  && targetm.scalar_mode_supported_p (*cand)
+	  && targetm.libgcc_floating_mode_supported_p (*cand))
 	return cand;
     }
-  return VOIDmode;
+  return opt_scalar_float_mode ();
 }
 
 /* Make some target macros useable by target-independent code.  */
Index: gcc/tree.c
===================================================================
--- gcc/tree.c	2017-06-30 12:50:37.494697187 +0100
+++ gcc/tree.c	2017-07-13 09:18:26.920877340 +0100
@@ -10474,8 +10474,8 @@ build_common_tree_nodes (bool signed_cha
     {
       int n = floatn_nx_types[i].n;
       bool extended = floatn_nx_types[i].extended;
-      machine_mode mode = targetm.floatn_mode (n, extended);
-      if (mode == VOIDmode)
+      scalar_float_mode mode;
+      if (!targetm.floatn_mode (n, extended).exists (&mode))
 	continue;
       int precision = GET_MODE_PRECISION (mode);
       /* Work around the rs6000 KFmode having precision 113 not
