[gcc(refs/users/meissner/heads/work098)] Make __float128 use the _Float128 type.

[Michael Meissner]

https://gcc.gnu.org/g:f31e158c7aa36a870e21db15c89d97249cd1e576

commit f31e158c7aa36a870e21db15c89d97249cd1e576
Author: Michael Meissner <meissner@linux.ibm.com>
Date:   Thu Aug 18 20:38:56 2022 -0400

    Make __float128 use the _Float128 type.
    
    Currently GCC uses the long double type node for __float128 if long double is
    IEEE 128-bit.  It did not use the node for _Float128.
    
    This showed up if you call the nansq function to make a signaling NaN (nansq is
    mapped to nansf128).  Because the type node for _Float128 is different from
    __float128, the machine independent code converts signaling NaNs to quiet NaNs
    if the types are  not compatible.  The following tests used to fail when run on
    a system where long double is IEEE 128-bit:
    
            gcc.dg/torture/float128-nan.c
            gcc.target/powerpc/nan128-1.c
    
    This patch makes both __float128 and _Float128 use the same type node.
    
    2022-08-17   Michael Meissner  <meissner@linux.ibm.com>
    
    gcc/
    
            * config/rs6000/rs6000-builtin.cc (rs6000_init_builtins): Always use the
            _Float128 type for __float128.  Don't use the long double type.

Diff:
---
 gcc/config/rs6000/rs6000-builtin.cc | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/gcc/config/rs6000/rs6000-builtin.cc b/gcc/config/rs6000/rs6000-builtin.cc
index 70680890415..10abc8463e8 100644
--- a/gcc/config/rs6000/rs6000-builtin.cc
+++ b/gcc/config/rs6000/rs6000-builtin.cc
@@ -733,10 +733,7 @@ rs6000_init_builtins (void)
 
   if (TARGET_FLOAT128_TYPE)
     {
-      if (TARGET_IEEEQUAD && TARGET_LONG_DOUBLE_128)
-	ieee128_float_type_node = long_double_type_node;
-      else
-	ieee128_float_type_node = float128_type_node;
+      ieee128_float_type_node = float128_type_node;
       t = build_qualified_type (ieee128_float_type_node, TYPE_QUAL_CONST);
       lang_hooks.types.register_builtin_type (ieee128_float_type_node,
 					      "__ieee128");