Set mode of decimal floats before calling layout_type

[Richard Sandiford <richard.sandiford@arm.com>]

Previously decimal floating-point types were created and laid
out as binary floating-point types, then the caller changed
the mode to a decimal mode later.  The problem with that
approach is that not all targets support an equivalent binary
floating-point mode.  When they didn't, we would give the
type BLKmode and lay it out as a zero-sized type.

This probably had no effect in practice.  If a target doesn't
support a binary mode then it's unlikely to support the decimal
equivalent either.  However, with the stricter mode checking
added by later patches, we would assert if a scalar floating-
point type didn't have a scalar floating-point mode.

Tested on aarch64-linux-gnu, x86_64-linux-gnu and powerpc64-linux-gnu.
OK to install?

Thanks,
Richard


[ This patch is part of the SVE series posted here:
  https://gcc.gnu.org/ml/gcc/2016-11/msg00030.html ]

gcc/
2016-11-16  Richard Sandiford  <richard.sandiford@arm.com>
	    Alan Hayward  <alan.hayward@arm.com>
	    David Sherwood  <david.sherwood@arm.com>

	* stor-layout.c (layout_type): Allow the caller to set the mode of
	a float type.  Only choose one here if the mode is still VOIDmode.
	* tree.c (build_common_tree_nodes): Set the type mode of decimal
	floats before calling layout_type.
	* config/rs6000/rs6000.c (rs6000_init_builtins): Likewise.

diff --git a/gcc/config/rs6000/rs6000.c b/gcc/config/rs6000/rs6000.c
index fa62e2e..a789ea1 100644
--- a/gcc/config/rs6000/rs6000.c
+++ b/gcc/config/rs6000/rs6000.c
@@ -16793,8 +16793,8 @@ rs6000_init_builtins (void)
     {
       ibm128_float_type_node = make_node (REAL_TYPE);
       TYPE_PRECISION (ibm128_float_type_node) = 128;
-      layout_type (ibm128_float_type_node);
       SET_TYPE_MODE (ibm128_float_type_node, IFmode);
+      layout_type (ibm128_float_type_node);
 
       lang_hooks.types.register_builtin_type (ibm128_float_type_node,
 					      "__ibm128");
@@ -16813,8 +16813,8 @@ rs6000_init_builtins (void)
     {
       ieee128_float_type_node = make_node (REAL_TYPE);
       TYPE_PRECISION (ibm128_float_type_node) = 128;
-      layout_type (ieee128_float_type_node);
       SET_TYPE_MODE (ieee128_float_type_node, KFmode);
+      layout_type (ieee128_float_type_node);
 
       /* If we are not exporting the __float128/_Float128 keywords, we need a
 	 keyword to get the types created.  Use __ieee128 as the dummy
diff --git a/gcc/stor-layout.c b/gcc/stor-layout.c
index 9f8efcb..5a4bcf1 100644
--- a/gcc/stor-layout.c
+++ b/gcc/stor-layout.c
@@ -2135,8 +2135,11 @@ layout_type (tree type)
       break;
 
     case REAL_TYPE:
-      SET_TYPE_MODE (type,
-		     mode_for_size (TYPE_PRECISION (type), MODE_FLOAT, 0));
+      /* Allow the caller to choose the type mode, which is how decimal
+	 floats are distinguished from binary ones.  */
+      if (TYPE_MODE (type) == VOIDmode)
+	SET_TYPE_MODE (type,
+		       mode_for_size (TYPE_PRECISION (type), MODE_FLOAT, 0));
       TYPE_SIZE (type) = bitsize_int (GET_MODE_BITSIZE (TYPE_MODE (type)));
       TYPE_SIZE_UNIT (type) = size_int (GET_MODE_SIZE (TYPE_MODE (type)));
       break;
diff --git a/gcc/tree.c b/gcc/tree.c
index a4c5b1b..f60f331 100644
--- a/gcc/tree.c
+++ b/gcc/tree.c
@@ -10385,20 +10385,20 @@ build_common_tree_nodes (bool signed_char)
   /* Decimal float types. */
   dfloat32_type_node = make_node (REAL_TYPE);
   TYPE_PRECISION (dfloat32_type_node) = DECIMAL32_TYPE_SIZE;
-  layout_type (dfloat32_type_node);
   SET_TYPE_MODE (dfloat32_type_node, SDmode);
+  layout_type (dfloat32_type_node);
   dfloat32_ptr_type_node = build_pointer_type (dfloat32_type_node);
 
   dfloat64_type_node = make_node (REAL_TYPE);
   TYPE_PRECISION (dfloat64_type_node) = DECIMAL64_TYPE_SIZE;
-  layout_type (dfloat64_type_node);
   SET_TYPE_MODE (dfloat64_type_node, DDmode);
+  layout_type (dfloat64_type_node);
   dfloat64_ptr_type_node = build_pointer_type (dfloat64_type_node);
 
   dfloat128_type_node = make_node (REAL_TYPE);
   TYPE_PRECISION (dfloat128_type_node) = DECIMAL128_TYPE_SIZE;
-  layout_type (dfloat128_type_node);
   SET_TYPE_MODE (dfloat128_type_node, TDmode);
+  layout_type (dfloat128_type_node);
   dfloat128_ptr_type_node = build_pointer_type (dfloat128_type_node);
 
   complex_integer_type_node = build_complex_type (integer_type_node, true);