Prevent all uses of DFP when unsupported (PR c/91985).

Code that directly uses _Decimal* types on architectures not
supporting DFP is properly diagnosed ("error: decimal floating-point
not supported for this target"), via a call to
targetm.decimal_float_supported_p, if the _Decimal32, _Decimal64 or
_Decimal128 keywords are used to access it.  Use via mode attributes
is also diagnosed ("unable to emulate 'SD'"); so is use of the
FLOAT_CONST_DECIMAL64 pragma.  However, it is possible to access those
types via typeof applied to constants or built-in functions without
such an error.  I expect that there are ways to get an ICE from this;
certainly it uses a completely undefined ABI.

This patch arranges for the types not to exist in the compiler at all
when DFP is not supported.  As is done with unsupported _FloatN /
_FloatNx types, the global tree nodes are left as NULL_TREE, and the
built-in function machinery is made to use error_mark_node for them in
that case in builtin-types.def, so that the built-in functions are
unavailable.  Code handling constants is adjusted to give an error,
and other code that might not work with the global tree nodes being
NULL_TREE is also updated.

Bootstrapped with no regressions for x86_64-pc-linux-gnu.  Also tested
with no regressions for cross to aarch64-linux-gnu, as a configuration
without DFP support.

	PR c/91985
gcc:
	* builtin-types.def (BT_DFLOAT32, BT_DFLOAT64, BT_DFLOAT128)
	(BT_DFLOAT32_PTR, BT_DFLOAT64_PTR, BT_DFLOAT128_PTR): Define to
	error_mark_node if corresponding global tree node is NULL.
	* tree.c (build_common_tree_nodes): Do not initialize
	dfloat32_type_node, dfloat64_type_node or dfloat128_type_node if
	decimal floating-point not supported.

gcc/c:
	* c-decl.c (finish_declspecs): Use int instead of decimal
	floating-point types if decimal floating-point not supported.

gcc/c-family:
	* c-common.c (c_common_type_for_mode): Handle decimal
	floating-point types being NULL_TREE.
	* c-format.c (get_format_for_type_1): Handle specified types being
	NULL_TREE.
	* c-lex.c (interpret_float): Give an error for decimal
	floating-point constants when decimal floating-point not
	supported.

gcc/lto:
	* lto-lang.c (lto_type_for_mode): Handle decimal floating-point
	types being NULL_TREE.

gcc/testsuite:
	* gcc.dg/c2x-no-dfp-1.c, gcc.dg/gnu2x-builtins-no-dfp-1.c: New
	tests.
	* gcc.dg/fltconst-pedantic-dfp.c: Expect errors when decimal
	floating-point not supported.

From-SVN: r278684

15 files changed, 134 insertions, 32 deletions

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 58be9e9410b..2b63623f56d 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,5 +1,15 @@
 2019-11-25  Joseph Myers  <joseph@codesourcery.com>
 
+	PR c/91985
+	* builtin-types.def (BT_DFLOAT32, BT_DFLOAT64, BT_DFLOAT128)
+	(BT_DFLOAT32_PTR, BT_DFLOAT64_PTR, BT_DFLOAT128_PTR): Define to
+	error_mark_node if corresponding global tree node is NULL.
+	* tree.c (build_common_tree_nodes): Do not initialize
+	dfloat32_type_node, dfloat64_type_node or dfloat128_type_node if
+	decimal floating-point not supported.
+
+2019-11-25  Joseph Myers  <joseph@codesourcery.com>
+
 	* attribs.c (decl_attributes): Do not ignore C++11 attributes on
 	types.
 
diff --git a/gcc/builtin-types.def b/gcc/builtin-types.def
index e5c9e063c48..800b751de6d 100644
--- a/gcc/builtin-types.def
+++ b/gcc/builtin-types.def
@@ -136,12 +136,24 @@ DEF_PRIMITIVE_TYPE (BT_WINT, wint_type_node)
 DEF_PRIMITIVE_TYPE (BT_STRING, string_type_node)
 DEF_PRIMITIVE_TYPE (BT_CONST_STRING, const_string_type_node)
 
-DEF_PRIMITIVE_TYPE (BT_DFLOAT32, dfloat32_type_node)
-DEF_PRIMITIVE_TYPE (BT_DFLOAT64, dfloat64_type_node)
-DEF_PRIMITIVE_TYPE (BT_DFLOAT128, dfloat128_type_node)
-DEF_PRIMITIVE_TYPE (BT_DFLOAT32_PTR, dfloat32_ptr_type_node)
-DEF_PRIMITIVE_TYPE (BT_DFLOAT64_PTR, dfloat64_ptr_type_node)
-DEF_PRIMITIVE_TYPE (BT_DFLOAT128_PTR, dfloat128_ptr_type_node)
+DEF_PRIMITIVE_TYPE (BT_DFLOAT32, (dfloat32_type_node
+				  ? dfloat32_type_node
+				  : error_mark_node))
+DEF_PRIMITIVE_TYPE (BT_DFLOAT64, (dfloat64_type_node
+				  ? dfloat64_type_node
+				  : error_mark_node))
+DEF_PRIMITIVE_TYPE (BT_DFLOAT128, (dfloat128_type_node
+				   ? dfloat128_type_node
+				   : error_mark_node))
+DEF_PRIMITIVE_TYPE (BT_DFLOAT32_PTR, (dfloat32_ptr_type_node
+				      ? dfloat32_ptr_type_node
+				      : error_mark_node))
+DEF_PRIMITIVE_TYPE (BT_DFLOAT64_PTR, (dfloat64_ptr_type_node
+				      ? dfloat64_ptr_type_node
+				      : error_mark_node))
+DEF_PRIMITIVE_TYPE (BT_DFLOAT128_PTR, (dfloat128_ptr_type_node
+				       ? dfloat128_ptr_type_node
+				       : error_mark_node))
 
 DEF_PRIMITIVE_TYPE (BT_VALIST_REF, va_list_ref_type_node)
 DEF_PRIMITIVE_TYPE (BT_VALIST_ARG, va_list_arg_type_node)
diff --git a/gcc/c-family/ChangeLog b/gcc/c-family/ChangeLog
index 281d7f409b7..30b5b6a4e07 100644
--- a/gcc/c-family/ChangeLog
+++ b/gcc/c-family/ChangeLog
@@ -1,3 +1,14 @@
+2019-11-25  Joseph Myers  <joseph@codesourcery.com>
+
+	PR c/91985
+	* c-common.c (c_common_type_for_mode): Handle decimal
+	floating-point types being NULL_TREE.
+	* c-format.c (get_format_for_type_1): Handle specified types being
+	NULL_TREE.
+	* c-lex.c (interpret_float): Give an error for decimal
+	floating-point constants when decimal floating-point not
+	supported.
+
 2019-11-23  Jakub Jelinek  <jakub@redhat.com>
 
 	PR middle-end/83859
diff --git a/gcc/c-family/c-common.c b/gcc/c-family/c-common.c
index 3e70b6d72f6..5b9af1a34b3 100644
--- a/gcc/c-family/c-common.c
+++ b/gcc/c-family/c-common.c
@@ -2321,11 +2321,14 @@ c_common_type_for_mode (machine_mode mode, int unsignedp)
 	return build_vector_type_for_mode (inner_type, mode);
     }
 
-  if (mode == TYPE_MODE (dfloat32_type_node))
+  if (dfloat32_type_node != NULL_TREE
+      && mode == TYPE_MODE (dfloat32_type_node))
     return dfloat32_type_node;
-  if (mode == TYPE_MODE (dfloat64_type_node))
+  if (dfloat64_type_node != NULL_TREE
+      && mode == TYPE_MODE (dfloat64_type_node))
     return dfloat64_type_node;
-  if (mode == TYPE_MODE (dfloat128_type_node))
+  if (dfloat128_type_node != NULL_TREE
+      && mode == TYPE_MODE (dfloat128_type_node))
     return dfloat128_type_node;
 
   if (ALL_SCALAR_FIXED_POINT_MODE_P (mode))
diff --git a/gcc/c-family/c-format.c b/gcc/c-family/c-format.c
index d70d1e0f9c2..519bc8f0af1 100644
--- a/gcc/c-family/c-format.c
+++ b/gcc/c-family/c-format.c
@@ -4390,7 +4390,7 @@ get_format_for_type_1 (const format_kind_info *fki, tree arg_type,
       for (int i = 0; i < FMT_LEN_MAX; i++)
 	{
 	  const format_type_detail *ftd = &spec->types[i];
-	  if (!ftd->type)
+	  if (!ftd->type || *ftd->type == NULL_TREE)
 	    continue;
 	  if (matching_type_p (*ftd->type, effective_arg_type))
 	    {
diff --git a/gcc/c-family/c-lex.c b/gcc/c-family/c-lex.c
index d446633f814..107c4c3e931 100644
--- a/gcc/c-family/c-lex.c
+++ b/gcc/c-family/c-lex.c
@@ -877,7 +877,12 @@ interpret_float (const cpp_token *token, unsigned int flags,
 
   /* Decode type based on width and properties. */
   if (flags & CPP_N_DFLOAT)
-    if ((flags & CPP_N_WIDTH) == CPP_N_LARGE)
+    if (!targetm.decimal_float_supported_p ())
+      {
+	error ("decimal floating-point not supported for this target");
+	return error_mark_node;
+      }
+    else if ((flags & CPP_N_WIDTH) == CPP_N_LARGE)
       type = dfloat128_type_node;
     else if ((flags & CPP_N_WIDTH) == CPP_N_SMALL)
       type = dfloat32_type_node;
diff --git a/gcc/c/ChangeLog b/gcc/c/ChangeLog
index 9f0b8cee6eb..b9ec9777dd2 100644
--- a/gcc/c/ChangeLog
+++ b/gcc/c/ChangeLog
@@ -1,5 +1,11 @@
 2019-11-25  Joseph Myers  <joseph@codesourcery.com>
 
+	PR c/91985
+	* c-decl.c (finish_declspecs): Use int instead of decimal
+	floating-point types if decimal floating-point not supported.
+
+2019-11-25  Joseph Myers  <joseph@codesourcery.com>
+
 	* c-tree.h (struct c_declarator): Use a structure for id member.
 	* c-decl.c (grokdeclarator): Extract attributes from cdk_id
 	declarators at the start, not when handling individual declarators
diff --git a/gcc/c/c-decl.c b/gcc/c/c-decl.c
index a14f7821d1e..292a4cc849b 100644
--- a/gcc/c/c-decl.c
+++ b/gcc/c/c-decl.c
@@ -11633,7 +11633,9 @@ finish_declspecs (struct c_declspecs *specs)
     case cts_dfloat128:
       gcc_assert (!specs->long_p && !specs->long_long_p && !specs->short_p
 		  && !specs->signed_p && !specs->unsigned_p && !specs->complex_p);
-      if (specs->typespec_word == cts_dfloat32)
+      if (!targetm.decimal_float_supported_p ())
+	specs->type = integer_type_node;
+      else if (specs->typespec_word == cts_dfloat32)
 	specs->type = dfloat32_type_node;
       else if (specs->typespec_word == cts_dfloat64)
 	specs->type = dfloat64_type_node;
diff --git a/gcc/lto/ChangeLog b/gcc/lto/ChangeLog
index cdf6964fbb7..df9ddfa3432 100644
--- a/gcc/lto/ChangeLog
+++ b/gcc/lto/ChangeLog
@@ -1,3 +1,9 @@
+2019-11-25  Joseph Myers  <joseph@codesourcery.com>
+
+	PR c/91985
+	* lto-lang.c (lto_type_for_mode): Handle decimal floating-point
+	types being NULL_TREE.
+
 2019-11-22  Jan Hubicka  <jh@suse.cz>
 	
 	* lto.c (lto_wpa_write_files): Call memory_block_pool::trim.
diff --git a/gcc/lto/lto-lang.c b/gcc/lto/lto-lang.c
index 3e37c37fa46..f8278676d5d 100644
--- a/gcc/lto/lto-lang.c
+++ b/gcc/lto/lto-lang.c
@@ -1051,11 +1051,14 @@ lto_type_for_mode (machine_mode mode, int unsigned_p)
 	return build_vector_type_for_mode (inner_type, mode);
     }
 
-  if (mode == TYPE_MODE (dfloat32_type_node))
+  if (dfloat32_type_node != NULL_TREE
+      && mode == TYPE_MODE (dfloat32_type_node))
     return dfloat32_type_node;
-  if (mode == TYPE_MODE (dfloat64_type_node))
+  if (dfloat64_type_node != NULL_TREE
+      && mode == TYPE_MODE (dfloat64_type_node))
     return dfloat64_type_node;
-  if (mode == TYPE_MODE (dfloat128_type_node))
+  if (dfloat128_type_node != NULL_TREE
+      && mode == TYPE_MODE (dfloat128_type_node))
     return dfloat128_type_node;
 
   if (ALL_SCALAR_FIXED_POINT_MODE_P (mode))
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 5ded904a5f1..6431a093b52 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,5 +1,13 @@
 2019-11-25  Joseph Myers  <joseph@codesourcery.com>
 
+	PR c/91985
+	* gcc.dg/c2x-no-dfp-1.c, gcc.dg/gnu2x-builtins-no-dfp-1.c: New
+	tests.
+	* gcc.dg/fltconst-pedantic-dfp.c: Expect errors when decimal
+	floating-point not supported.
+
+2019-11-25  Joseph Myers  <joseph@codesourcery.com>
+
 	* gcc.dg/gnu2x-attrs-1.c: Do not expect message about attributes
 	appertaining to types.
 	* gcc.dg/gnu2x-attrs-2.c: New test.
diff --git a/gcc/testsuite/gcc.dg/c2x-no-dfp-1.c b/gcc/testsuite/gcc.dg/c2x-no-dfp-1.c
new file mode 100644
index 00000000000..2cfbb6cad26
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/c2x-no-dfp-1.c
@@ -0,0 +1,12 @@
+/* Test DFP types and constants rejected if no DFP support.  Bug
+   91985.  */
+/* { dg-do compile { target { ! dfp } } } */
+/* { dg-options "-std=c2x" } */
+
+_Decimal32 d32a; /* { dg-error "not supported" } */
+_Decimal64 d64a; /* { dg-error "not supported" } */
+_Decimal128 d128a; /* { dg-error "not supported" } */
+
+_Bool d32b = 1.0DF; /* { dg-error "not supported" } */
+_Bool d64b = 1.0DD; /* { dg-error "not supported" } */
+_Bool d128b = 1.0DL; /* { dg-error "not supported" } */
diff --git a/gcc/testsuite/gcc.dg/fltconst-pedantic-dfp.c b/gcc/testsuite/gcc.dg/fltconst-pedantic-dfp.c
index d0d1c4c52fc..6ff3091ce6a 100644
--- a/gcc/testsuite/gcc.dg/fltconst-pedantic-dfp.c
+++ b/gcc/testsuite/gcc.dg/fltconst-pedantic-dfp.c
@@ -2,5 +2,8 @@
 /* { dg-options "-pedantic" } */
 
 double a = 1.dl;	/* { dg-warning "decimal float" } */
+/* { dg-error "not supported for this target" "not supported" { target { ! dfp } } .-1 } */
 double b = 1.df;	/* { dg-warning "decimal float" } */
+/* { dg-error "not supported for this target" "not supported" { target { ! dfp } } .-1 } */
 double c = 1.dd;	/* { dg-warning "decimal float" } */
+/* { dg-error "not supported for this target" "not supported" { target { ! dfp } } .-1 } */
diff --git a/gcc/testsuite/gcc.dg/gnu2x-builtins-no-dfp-1.c b/gcc/testsuite/gcc.dg/gnu2x-builtins-no-dfp-1.c
new file mode 100644
index 00000000000..853a56e9a85
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/gnu2x-builtins-no-dfp-1.c
@@ -0,0 +1,18 @@
+/* Test C2x built-in functions: test DFP built-in functions are not
+   available when no DFP support.  Bug 91985.  */
+/* { dg-do compile { target { ! dfp } } } */
+/* { dg-options "-std=gnu2x" } */
+
+int fabsd32 (void);
+int fabsd64 (void);
+int fabsd128 (void);
+int nand32 (void);
+int nand64 (void);
+int nand128 (void);
+
+__typeof__ (__builtin_fabsd32 (0)) d32; /* { dg-warning "implicit" } */
+__typeof__ (__builtin_fabsd64 (0)) d64; /* { dg-warning "implicit" } */
+__typeof__ (__builtin_fabsd128 (0)) d128; /* { dg-warning "implicit" } */
+__typeof__ (__builtin_nand32 (0)) d32n; /* { dg-warning "implicit" } */
+__typeof__ (__builtin_nand64 (0)) d64n; /* { dg-warning "implicit" } */
+__typeof__ (__builtin_nand128 (0)) d128n; /* { dg-warning "implicit" } */
diff --git a/gcc/tree.c b/gcc/tree.c
index f9ea79d1799..5ae250ee595 100644
--- a/gcc/tree.c
+++ b/gcc/tree.c
@@ -10334,23 +10334,26 @@ build_common_tree_nodes (bool signed_char)
   uint64_type_node = make_or_reuse_type (64, 1);
 
   /* Decimal float types. */
-  dfloat32_type_node = make_node (REAL_TYPE);
-  TYPE_PRECISION (dfloat32_type_node) = DECIMAL32_TYPE_SIZE;
-  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;
-  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;
-  SET_TYPE_MODE (dfloat128_type_node, TDmode);
-  layout_type (dfloat128_type_node);
-  dfloat128_ptr_type_node = build_pointer_type (dfloat128_type_node);
+  if (targetm.decimal_float_supported_p ())
+    {
+      dfloat32_type_node = make_node (REAL_TYPE);
+      TYPE_PRECISION (dfloat32_type_node) = DECIMAL32_TYPE_SIZE;
+      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;
+      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;
+      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);
   complex_float_type_node = build_complex_type (float_type_node, true);