rs6000: AIX long double builtins for 64 bit long double.

When long doubles are 64 bit, the AIX C library overrides the definitions
but GCC builtins point to 128 bit names.  This patch overrides the
builtins for fmodl, frexpl, ldexpl and modfl to refer to the 64 bit symbols.

Backport from mainline
2020-05-04  Clement Chigot  <clement.chigot@atos.net>
	    David Edelsohn  <dje.gcc@gmail.com>

	* config/rs6000/rs6000-call.c (rs6000_init_builtins): Override explicit
	for fmodl, frexpl, ldexpl and modfl builtins.

gcc/ChangeLog

+2020-05-12  David Edelsohn  <dje.gcc@gmail.com>
+
+	Backport from mainline
+	2020-05-04  Clement Chigot  <clement.chigot@atos.net>
+		    David Edelsohn  <dje.gcc@gmail.com>
+
+	* config/rs6000/rs6000-call.c (rs6000_init_builtins): Override explicit
+	for fmodl, frexpl, ldexpl and modfl builtins.
+
 2020-05-11  Sebastian Huber  <sebastian.huber@embedded-brains.de>
 
 	Backport from mainline

gcc/config/rs6000/rs6000-call.c

@@ -12070,10 +12070,28 @@ rs6000_init_builtins (void)
   def_builtin ("__builtin_cpu_is", ftype, RS6000_BUILTIN_CPU_IS);
   def_builtin ("__builtin_cpu_supports", ftype, RS6000_BUILTIN_CPU_SUPPORTS);
 
-  /* AIX libm provides clog as __clog.  */
-  if (TARGET_XCOFF &&
-      (tdecl = builtin_decl_explicit (BUILT_IN_CLOG)) != NULL_TREE)
-    set_user_assembler_name (tdecl, "__clog");
+  if (TARGET_XCOFF)
+    {
+      /* AIX libm provides clog as __clog.  */
+      if ((tdecl = builtin_decl_explicit (BUILT_IN_CLOG)) != NULL_TREE)
+	set_user_assembler_name (tdecl, "__clog");
+
+      /* When long double is 64 bit, some long double builtins of libc
+	 functions (like __builtin_frexpl) must call the double version
+	 (frexp) not the long double version (frexpl) that expects a 128 bit
+	 argument.  */
+      if (! TARGET_LONG_DOUBLE_128)
+	{
+	  if ((tdecl = builtin_decl_explicit (BUILT_IN_FMODL)) != NULL_TREE)
+	    set_user_assembler_name (tdecl, "fmod");
+	  if ((tdecl = builtin_decl_explicit (BUILT_IN_FREXPL)) != NULL_TREE)
+	    set_user_assembler_name (tdecl, "frexp");
+	  if ((tdecl = builtin_decl_explicit (BUILT_IN_LDEXPL)) != NULL_TREE)
+	    set_user_assembler_name (tdecl, "ldexp");
+	  if ((tdecl = builtin_decl_explicit (BUILT_IN_MODFL)) != NULL_TREE)
+	    set_user_assembler_name (tdecl, "modf");
+	}
+    }
 
 #ifdef SUBTARGET_INIT_BUILTINS
   SUBTARGET_INIT_BUILTINS;