builtins: Add DFP signaling NaN built-in functions

Add built-in functions __builtin_nansd32, __builtin_nansd64 and
__builtin_nansd128 to return signaling NaNs of decimal floating-point
types, analogous to the functions already present for binary
floating-point types.

This patch, independent of
<https://gcc.gnu.org/pipermail/gcc-patches/2020-October/557136.html>
(pending review), is in preparation for adding the <float.h> macros
for such signaling NaNs that are in C2x, analogous to the macros for
other types that are in that patch.

Bootstrapped with no regressions for x86_64-pc-linux-gnu.  Also ran
the new tests for powerpc64le-linux-gnu to confirm they do work in the
case (hardware DFP) where floating-point exceptions are supported for
DFP.

gcc/
2020-11-06  Joseph Myers  <joseph@codesourcery.com>

	* builtins.def (BUILT_IN_NANSD32, BUILT_IN_NANSD64)
	(BUILT_IN_NANSD128): New built-in functions.
	* fold-const-call.c (fold_const_call): Handle the new built-in
	functions.
	* doc/extend.texi (__builtin_nansd32, __builtin_nansd64)
	(__builtin_nansd128): Document.
	* doc/sourcebuild.texi (Effective-Target Keywords): Document
	fenv_exceptions_dfp.

gcc/testsuite/
2020-11-06  Joseph Myers  <joseph@codesourcery.com>

	* lib/target-supports.exp
	(check_effective_target_fenv_exceptions_dfp): New.
	* gcc.dg/dfp/builtin-snan-1.c, gcc.dg/dfp/builtin-snan-2.c: New
	tests.

gcc/builtins.def

@@ -518,6 +518,9 @@ DEF_GCC_BUILTIN        (BUILT_IN_NANSF, "nansf", BT_FN_FLOAT_CONST_STRING, ATTR_
 DEF_GCC_BUILTIN        (BUILT_IN_NANSL, "nansl", BT_FN_LONGDOUBLE_CONST_STRING, ATTR_CONST_NOTHROW_NONNULL)
 DEF_GCC_FLOATN_NX_BUILTINS (BUILT_IN_NANS, "nans", NAN_TYPE, ATTR_CONST_NOTHROW_NONNULL)
 #undef NAN_TYPE
+DEF_GCC_BUILTIN        (BUILT_IN_NANSD32, "nansd32", BT_FN_DFLOAT32_CONST_STRING, ATTR_CONST_NOTHROW_NONNULL)
+DEF_GCC_BUILTIN        (BUILT_IN_NANSD64, "nansd64", BT_FN_DFLOAT64_CONST_STRING, ATTR_CONST_NOTHROW_NONNULL)
+DEF_GCC_BUILTIN        (BUILT_IN_NANSD128, "nansd128", BT_FN_DFLOAT128_CONST_STRING, ATTR_CONST_NOTHROW_NONNULL)
 DEF_C99_BUILTIN        (BUILT_IN_NEARBYINT, "nearbyint", BT_FN_DOUBLE_DOUBLE, ATTR_CONST_NOTHROW_LEAF_LIST)
 DEF_C99_BUILTIN        (BUILT_IN_NEARBYINTF, "nearbyintf", BT_FN_FLOAT_FLOAT, ATTR_CONST_NOTHROW_LEAF_LIST)
 DEF_C99_BUILTIN        (BUILT_IN_NEARBYINTL, "nearbyintl", BT_FN_LONGDOUBLE_LONGDOUBLE, ATTR_CONST_NOTHROW_LEAF_LIST)

gcc/doc/extend.texi

@@ -13865,6 +13865,18 @@ to be a signaling NaN@.  The @code{nans} function is proposed by
 @uref{http://www.open-std.org/jtc1/sc22/wg14/www/docs/n965.htm,,WG14 N965}.
 @end deftypefn
 
+@deftypefn {Built-in Function} _Decimal32 __builtin_nansd32 (const char *str)
+Similar to @code{__builtin_nans}, except the return type is @code{_Decimal32}.
+@end deftypefn
+
+@deftypefn {Built-in Function} _Decimal64 __builtin_nansd64 (const char *str)
+Similar to @code{__builtin_nans}, except the return type is @code{_Decimal64}.
+@end deftypefn
+
+@deftypefn {Built-in Function} _Decimal128 __builtin_nansd128 (const char *str)
+Similar to @code{__builtin_nans}, except the return type is @code{_Decimal128}.
+@end deftypefn
+
 @deftypefn {Built-in Function} float __builtin_nansf (const char *str)
 Similar to @code{__builtin_nans}, except the return type is @code{float}.
 @end deftypefn

gcc/doc/sourcebuild.texi

@@ -2356,6 +2356,11 @@ Target provides @file{fenv.h} include file.
 Target supports @file{fenv.h} with all the standard IEEE exceptions
 and floating-point exceptions are raised by arithmetic operations.
 
+@item fenv_exceptions_dfp
+Target supports @file{fenv.h} with all the standard IEEE exceptions
+and floating-point exceptions are raised by arithmetic operations for
+decimal floating point.
+
 @item fileio
 Target offers such file I/O library functions as @code{fopen},
 @code{fclose}, @code{tmpnam}, and @code{remove}.  This is a link-time

gcc/fold-const-call.c

@@ -1300,6 +1300,9 @@ fold_const_call (combined_fn fn, tree type, tree arg)
 
     CASE_CFN_NANS:
     CASE_FLT_FN_FLOATN_NX (CFN_BUILT_IN_NANS):
+    case CFN_BUILT_IN_NANSD32:
+    case CFN_BUILT_IN_NANSD64:
+    case CFN_BUILT_IN_NANSD128:
       return fold_const_builtin_nan (type, arg, false);
 
     case CFN_REDUC_PLUS:

gcc/testsuite/gcc.dg/dfp/builtin-snan-1.c

@@ -0,0 +1,23 @@
+/* Test __builtin_nansd* functions.  Test not requiring runtime
+   exceptions support.  */
+/* { dg-do run } */
+/* { dg-options "" } */
+
+volatile _Decimal32 d32 = __builtin_nansd32 ("");
+volatile _Decimal64 d64 = __builtin_nansd64 ("");
+volatile _Decimal128 d128 = __builtin_nansd128 ("");
+
+extern void abort (void);
+extern void exit (int);
+
+int
+main (void)
+{
+  if (!__builtin_isnan (d32))
+    abort ();
+  if (!__builtin_isnan (d64))
+    abort ();
+  if (!__builtin_isnan (d128))
+    abort ();
+  exit (0);
+}

gcc/testsuite/gcc.dg/dfp/builtin-snan-2.c

@@ -0,0 +1,44 @@
+/* Test __builtin_nansd* functions.  Test requiring runtime exceptions
+   support.  */
+/* { dg-do run } */
+/* { dg-require-effective-target fenv_exceptions_dfp } */
+/* { dg-options "" } */
+
+#include <fenv.h>
+
+volatile _Decimal32 d32 = __builtin_nansd32 ("");
+volatile _Decimal64 d64 = __builtin_nansd64 ("");
+volatile _Decimal128 d128 = __builtin_nansd128 ("");
+
+extern void abort (void);
+extern void exit (int);
+
+int
+main (void)
+{
+  feclearexcept (FE_ALL_EXCEPT);
+  d32 += d32;
+  if (!fetestexcept (FE_INVALID))
+    abort ();
+  feclearexcept (FE_ALL_EXCEPT);
+  d32 += d32;
+  if (fetestexcept (FE_INVALID))
+    abort ();
+  feclearexcept (FE_ALL_EXCEPT);
+  d64 += d64;
+  if (!fetestexcept (FE_INVALID))
+    abort ();
+  feclearexcept (FE_ALL_EXCEPT);
+  d64 += d64;
+  if (fetestexcept (FE_INVALID))
+    abort ();
+  feclearexcept (FE_ALL_EXCEPT);
+  d128 += d128;
+  if (!fetestexcept (FE_INVALID))
+    abort ();
+  feclearexcept (FE_ALL_EXCEPT);
+  d128 += d128;
+  if (fetestexcept (FE_INVALID))
+    abort ();
+  exit (0);
+}

gcc/testsuite/lib/target-supports.exp

@@ -9693,6 +9693,44 @@ proc check_effective_target_fenv_exceptions {} {
     } [add_options_for_ieee "-std=gnu99"]]
 }
 
+# Return 1 if <fenv.h> is available with all the standard IEEE
+# exceptions and floating-point exceptions are raised by arithmetic
+# operations for decimal floating point.  (If the target requires
+# special options for "inexact" exceptions, those need to be specified
+# in the testcases.)
+
+proc check_effective_target_fenv_exceptions_dfp {} {
+    return [check_runtime fenv_exceptions_dfp {
+	#include <fenv.h>
+	#include <stdlib.h>
+	#ifndef FE_DIVBYZERO
+	# error Missing FE_DIVBYZERO
+	#endif
+	#ifndef FE_INEXACT
+	# error Missing FE_INEXACT
+	#endif
+	#ifndef FE_INVALID
+	# error Missing FE_INVALID
+	#endif
+	#ifndef FE_OVERFLOW
+	# error Missing FE_OVERFLOW
+	#endif
+	#ifndef FE_UNDERFLOW
+	# error Missing FE_UNDERFLOW
+	#endif
+	volatile _Decimal64 a = 0.0DD, r;
+	int
+	main (void)
+	{
+	  r = a / a;
+	  if (fetestexcept (FE_INVALID))
+	    exit (0);
+	  else
+	    abort ();
+	}
+    } [add_options_for_ieee "-std=gnu99"]]
+}
+
 # Return 1 if -fexceptions is supported.
 
 proc check_effective_target_exceptions {} {