PR target/107299: Fix build issue when long double is IEEE 128-bit

This patch updates the IEEE 128-bit types used in libgcc.

At the moment, we cannot build GCC when the target uses IEEE 128-bit long
doubles, such as building the compiler for a native Fedora 36 system.  The
build dies when it is trying to build the _mulkc3.c and _divkc3 modules.

This patch changes libgcc to use long double for the IEEE 128-bit base type if
long double is IEEE 128-bit, and it uses _Float128 otherwise.  The built-in
functions are adjusted to be the correct version based on the IEEE 128-bit base
type used.

While it is desirable to ultimately have __float128 and _Float128 use the same
internal type and mode within GCC, at present if you use the option
-mabi=ieeelongdouble, the __float128 type will use the long double type and not
the _Float128 type.  We get an internal compiler error if we combine the
signbitf128 built-in with a long double type.

I've gone through several iterations of trying to fix this within GCC, and
there are various problems that have come up.  I developed this alternative
patch that changes libgcc so that it does not tickle the issue.  I hope we can
fix the compiler at some point, but right now, this is preventing people on
Fedora 36 systems from building compilers where the default long double is IEEE
128-bit.

2023-03-06   Michael Meissner  <meissner@linux.ibm.com>

libgcc/

	PR target/107299
	* config/rs6000/_divkc3.c (COPYSIGN): Use the correct built-in based on
	whether long double is IBM or IEEE.
	(INFINITY): Likewise.
	(FABS): Likewise.
	* config/rs6000/_mulkc3.c (COPYSIGN): Likewise.
	(INFINITY): Likewise.
	* config/rs6000/quad-float128.h (TF): Remove definition.
	(TFtype): Define to be long double or _Float128.
	(TCtype): Define to be _Complex long double or _Complex _Float128.
	* libgcc2.h (TFtype): Allow machine config files to override this.
	(TCtype): Likewise.
	* soft-fp/quad.h (TFtype): Likewise.

libgcc/config/rs6000/_divkc3.c

@@ -26,9 +26,19 @@ see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
 #include "soft-fp.h"
 #include "quad-float128.h"
 
+/* Use the correct built-in function based on whether TFmode is _Float128 or
+   long double.  See quad-float128.h for more details.  */
+#ifndef __LONG_DOUBLE_IEEE128__
 #define COPYSIGN(x,y) __builtin_copysignf128 (x, y)
 #define INFINITY __builtin_inff128 ()
 #define FABS __builtin_fabsf128
+
+#else
+#define COPYSIGN(x,y) __builtin_copysignl (x, y)
+#define INFINITY __builtin_infl ()
+#define FABS __builtin_fabsl
+#endif
+
 #define isnan __builtin_isnan
 #define isinf __builtin_isinf
 #define isfinite __builtin_isfinite

libgcc/config/rs6000/_mulkc3.c

@@ -26,8 +26,17 @@ see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
 #include "soft-fp.h"
 #include "quad-float128.h"
 
+/* Use the correct built-in function based on whether TFmode is _Float128 or
+   long double.  See quad-float128.h for more details.  */
+#ifndef __LONG_DOUBLE_IEEE128__
 #define COPYSIGN(x,y) __builtin_copysignf128 (x, y)
 #define INFINITY __builtin_inff128 ()
+
+#else
+#define COPYSIGN(x,y) __builtin_copysignl (x, y)
+#define INFINITY __builtin_infl ()
+#endif
+
 #define isnan __builtin_isnan
 #define isinf __builtin_isinf
 

libgcc/config/rs6000/quad-float128.h

@@ -27,21 +27,37 @@
    License along with the GNU C Library; if not, see
    <http://www.gnu.org/licenses/>.  */
 
-/* quad.h defines the TFtype type by:
-   typedef float TFtype __attribute__ ((mode (TF)));
+/* Override the types for IEEE 128-bit scalar and complex.  We need to use the
+   same IEEE 128-bit type (either long double or _Float128) for both the
+   128-bit scalar type and for the base type in _Complex.  Otherwise, if
+   different types are used, there may be problems in mixing _Complex values
+   with the scalar value.
 
-   This define forces it to use KFmode (aka, ieee 128-bit floating point).
-   However, when the compiler's default is changed so that long double is IEEE
-   128-bit floating point, we need to go back to using TFmode and TCmode.  */
-#ifndef __LONG_DOUBLE_IEEE128__
-#define TF KF
+   We can't use _Compelx _float128 since GCC doesn't allow it.  It only allows
+   _Complex for _Float128 or for long double.
 
-/* We also need TCtype to represent complex ieee 128-bit float for
-   __mulkc3 and __divkc3.  */
-typedef __complex float TCtype __attribute__ ((mode (KC)));
+   We use _Float128 when long double is IBM double-double or 64-bit, and long
+   double when long double uses the IEEE 128-bit type.  We need to do this
+   because the compiler has a built-in prototype for __mulkc3 and __divkc3
+   using those types.  Since we are declaring these functions here, we need to
+   use the same type that the compiler uses (i.e. we can't just always use
+   _Float128).
+
+   Even though the type _Float128 and long double (when long double uses IEEE
+   128-bits) both hold IEEE 128-bit values, the front ends treat these as two
+   separate types.
+
+   The extension keyword __float128 is currently problematical because it can
+   either be a synonym for _Float128 (when long double is IBM) or for long
+   double (when long double is IEEE).  */
+
+#ifdef __LONG_DOUBLE_IEEE128__
+#define TFtype long double
+#define TCtype _Complex long double
 
 #else
-typedef __complex float TCtype __attribute__ ((mode (TC)));
+#define TFtype _Float128
+#define TCtype _Complex _Float128
 #endif
 
 /* Force the use of the VSX instruction set.  */

libgcc/libgcc2.h

@@ -156,9 +156,13 @@ typedef		float XFtype	__attribute__ ((mode (XF)));
 typedef _Complex float XCtype	__attribute__ ((mode (XC)));
 #endif
 #if LIBGCC2_HAS_TF_MODE
+#ifndef TFtype
 typedef		float TFtype	__attribute__ ((mode (TF)));
+#endif
+#ifndef TCtype
 typedef _Complex float TCtype	__attribute__ ((mode (TC)));
 #endif
+#endif
 
 typedef int cmp_return_type __attribute__((mode (__libgcc_cmp_return__)));
 typedef int shift_count_type __attribute__((mode (__libgcc_shift_count__)));

libgcc/soft-fp/quad.h

@@ -65,7 +65,9 @@
 #define _FP_HIGHBIT_DW_Q	\
   ((_FP_W_TYPE) 1 << (_FP_WFRACBITS_DW_Q - 1) % _FP_W_TYPE_SIZE)
 
+#ifndef TFtype
 typedef float TFtype __attribute__ ((mode (TF)));
+#endif
 
 #if _FP_W_TYPE_SIZE < 64