Implement __builtin_issignaling

The following patch implements a new builtin, __builtin_issignaling,
which can be used to implement the ISO/IEC TS 18661-1  issignaling
macro.

It is implemented as type-generic function, so there is just one
builtin, not many with various suffixes.
This patch doesn't address PR56831 nor PR58416, but I think compared to
using glibc issignaling macro could make some cases better (as
the builtin is expanded always inline and for SFmode/DFmode just
reinterprets a memory or pseudo register as SImode/DImode, so could
avoid some raising of exception + turning sNaN into qNaN before the
builtin can analyze it).

For floading point modes that do not have NaNs it will return 0,
otherwise I've tried to implement this for all the other supported
real formats.
It handles both the MIPS/PA floats where a sNaN has the mantissa
MSB set and the rest where a sNaN has it cleared, with the exception
of format which are known never to be in the MIPS/PA form.
The MIPS/PA floats are handled using a test like
(x & mask) == mask,
the other usually as
((x ^ bit) & mask) > val
where bit, mask and val are some constants.
IBM double double is done by doing DFmode test on the most significant
half, and Intel/Motorola extended (12 or 16 bytes) and IEEE quad are
handled by extracting 32-bit/16-bit words or 64-bit parts from the
value and testing those.
On x86, XFmode is handled by a special optab so that even pseudo numbers
are considered signaling, like in glibc and like the i386 specific testcase
tests.

2022-08-26  Jakub Jelinek  <jakub@redhat.com>

gcc/
	* builtins.def (BUILT_IN_ISSIGNALING): New built-in.
	* builtins.cc (expand_builtin_issignaling): New function.
	(expand_builtin_signbit): Don't overwrite target.
	(expand_builtin): Handle BUILT_IN_ISSIGNALING.
	(fold_builtin_classify): Likewise.
	(fold_builtin_1): Likewise.
	* optabs.def (issignaling_optab): New.
	* fold-const-call.cc (fold_const_call_ss): Handle
	BUILT_IN_ISSIGNALING.
	* config/i386/i386.md (issignalingxf2): New expander.
	* doc/extend.texi (__builtin_issignaling): Document.
	(__builtin_isinf, __builtin_isnan): Clarify behavior with
	-ffinite-math-only.
	* doc/md.texi (issignaling<mode>2): Likewise.
gcc/c-family/
	* c-common.cc (check_builtin_function_arguments): Handle
	BUILT_IN_ISSIGNALING.
gcc/c/
	* c-typeck.cc (convert_arguments): Handle BUILT_IN_ISSIGNALING.
gcc/fortran/
	* f95-lang.cc (gfc_init_builtin_functions): Initialize
	BUILT_IN_ISSIGNALING.
gcc/testsuite/
	* gcc.dg/torture/builtin-issignaling-1.c: New test.
	* gcc.dg/torture/builtin-issignaling-2.c: New test.
	* gcc.dg/torture/float16-builtin-issignaling-1.c: New test.
	* gcc.dg/torture/float32-builtin-issignaling-1.c: New test.
	* gcc.dg/torture/float32x-builtin-issignaling-1.c: New test.
	* gcc.dg/torture/float64-builtin-issignaling-1.c: New test.
	* gcc.dg/torture/float64x-builtin-issignaling-1.c: New test.
	* gcc.dg/torture/float128-builtin-issignaling-1.c: New test.
	* gcc.dg/torture/float128x-builtin-issignaling-1.c: New test.
	* gcc.target/i386/builtin-issignaling-1.c: New test.

2 files changed, 21 insertions, 0 deletions

diff --git a/gcc/doc/extend.texi b/gcc/doc/extend.texi
index 8a1d8fe..0fedab9 100644
--- a/gcc/doc/extend.texi
+++ b/gcc/doc/extend.texi
@@ -13003,6 +13003,7 @@ is called and the @var{flag} argument passed to it.
 @findex __builtin_isless
 @findex __builtin_islessequal
 @findex __builtin_islessgreater
+@findex __builtin_issignaling
 @findex __builtin_isunordered
 @findex __builtin_object_size
 @findex __builtin_powi
@@ -13558,6 +13559,8 @@ In the same fashion, GCC provides @code{fpclassify}, @code{isfinite},
 @code{isinf_sign}, @code{isnormal} and @code{signbit} built-ins used with
 @code{__builtin_} prefixed.  The @code{isinf} and @code{isnan}
 built-in functions appear both with and without the @code{__builtin_} prefix.
+With @code{-ffinite-math-only} option the @code{isinf} and @code{isnan}
+built-in functions will always return 0.
 
 GCC provides built-in versions of the ISO C99 floating-point rounding and
 exceptions handling functions @code{fegetround}, @code{feclearexcept} and
@@ -14491,6 +14494,20 @@ Similar to @code{__builtin_nans}, except the return type is
 @code{_Float@var{n}x}.
 @end deftypefn
 
+@deftypefn {Built-in Function} int __builtin_issignaling (...)
+Return non-zero if the argument is a signaling NaN and zero otherwise.
+Note while the parameter list is an
+ellipsis, this function only accepts exactly one floating-point
+argument.  GCC treats this parameter as type-generic, which means it
+does not do default promotion from float to double.
+This built-in function can work even without the non-default
+@code{-fsignaling-nans} option, although if a signaling NaN is computed,
+stored or passed as argument to some function other than this built-in
+in the current translation unit, it is safer to use @code{-fsignaling-nans}.
+With @code{-ffinite-math-only} option this built-in function will always
+return 0.
+@end deftypefn
+
 @deftypefn {Built-in Function} int __builtin_ffs (int x)
 Returns one plus the index of the least significant 1-bit of @var{x}, or
 if @var{x} is zero, returns zero.
diff --git a/gcc/doc/md.texi b/gcc/doc/md.texi
index b4dd4e7..3482554 100644
--- a/gcc/doc/md.texi
+++ b/gcc/doc/md.texi
@@ -6150,6 +6150,10 @@ floating-point mode.
 
 This pattern is not allowed to @code{FAIL}.
 
+@cindex @code{issignaling@var{m}2} instruction pattern
+@item @samp{issignaling@var{m}2}
+Set operand 0 to 1 if operand 1 is a signaling NaN and to 0 otherwise.
+
 @cindex @code{cadd90@var{m}3} instruction pattern
 @item @samp{cadd90@var{m}3}
 Perform vector add and subtract on even/odd number pairs.  The operation being