[gcc(refs/users/meissner/heads/work077)] Use system default for long double if not specified on PowerPC.

[gcc(refs/users/meissner/heads/work077)] Use system default for long double if not specified on PowerPC.

[Michael Meissner]

https://gcc.gnu.org/g:d9abbc644dc9470f539ab30d4ef96f99ec0e938b

commit d9abbc644dc9470f539ab30d4ef96f99ec0e938b
Author: Michael Meissner <meissner@linux.ibm.com>
Date:   Wed Jan 26 22:56:26 2022 -0500

    Use system default for long double if not specified on PowerPC.
    
    If the user did not specify a default long double format, use the long double
    default for the build compiler for the long double default.  This patch will
    allow compilers built on a distribution that has changed the 128-bit floating
    point format to use the default used on the system.
    
    I did a normal normal bootstrap and make check regression on a little
    endian power9 system and there were no regressions.
    
    In addition, I built a compiler where I configured the default to use IEEE
    128-bit floating point for long double.  I then used that compiler to
    build a bootstrap with this patch applied and I did not set the floating
    point format.  I verified that the compiler built with this patch defaults
    long double to be IEEE 128-bit.
    
    Can I apply this patch to the trunk for GCC 12?
    
    gcc/
    2022-01-26  Michael Meissner  <meissner@the-meissners.org>
    
            * config/rs6000/rs6000.cc (TARGET_IEEEQUAD_DEFAULT): If the
            compiler used to build the current compiler defaults to IEEE
            128-bit long double,  make that the default for this build.

Diff:
---
 gcc/config/rs6000/rs6000.cc | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/gcc/config/rs6000/rs6000.cc b/gcc/config/rs6000/rs6000.cc
index e5471da4504..f5c089a2a26 100644
--- a/gcc/config/rs6000/rs6000.cc
+++ b/gcc/config/rs6000/rs6000.cc
@@ -91,14 +91,22 @@
      explicitly redefine TARGET_IEEEQUAD and TARGET_IEEEQUAD_DEFAULT to 0, so
      those systems will not pick up this default.  This needs to be after all
      of the include files, so that POWERPC_LINUX and POWERPC_FREEBSD are
-     properly defined.  */
+     properly defined.
+
+     If we are being built by a compiler that uses IEEE 128-bit as the default
+     long double and no explicit long double format was selected, then also
+     default long double to IEEE 128-bit.  */
 #ifndef TARGET_IEEEQUAD_DEFAULT
 #if !defined (POWERPC_LINUX) && !defined (POWERPC_FREEBSD)
 #define TARGET_IEEEQUAD_DEFAULT 1
 #else
+#ifdef __LONG_DOUBLE_IEEE128__
+#define TARGET_IEEEQUAD_DEFAULT 1
+#else
 #define TARGET_IEEEQUAD_DEFAULT 0
 #endif
 #endif
+#endif
 
 /* Don't enable PC-relative addressing if the target does not support it.  */
 #ifndef PCREL_SUPPORTED_BY_OS