Patch [5 of 7]: Make -mtune=future be the same as -mtune=power10.

This patch makes -mcpu=future act like -mcpu=power10 in terms of tuning.  If
future patches changes the tuning, then this patch woucl be changed to use the
new tuning information.  Until there is different tuning, this patch does not
allow the user to explicitly use -mtune=future.

2024-02-14  Michael Meissner  <meissner@linux.ibm.com>

gcc/

	* config/rs6000/rs6000.cc (rs6000_option_override_internal): Make
	-mtune=future become -mtune=power10.

gcc/config/rs6000/rs6000.cc

@@ -3737,16 +3737,40 @@ rs6000_option_override_internal (bool global_init_p)
     rs6000_isa_flags &= ~OPTION_MASK_POWERPC64;
 #endif
 
+  /* At the moment, we don't have explicit -mtune=future support.  If the user
+     explicitly uses -mtune=future, give a warning.  If not, use the power10
+     tuning until future tuning is added.  */
   if (rs6000_tune_index >= 0)
-    tune_index = rs6000_tune_index;
+    {
+      enum processor_type cur_proc
+	= processor_target_table[rs6000_tune_index].processor;
+
+      if (cur_proc == PROCESSOR_FUTURE)
+	{
+	  warning (0, "%qs is not currently supported", "-mtune=future");
+	  rs6000_tune_index = rs6000_cpu_name_lookup ("power10");
+	}
+      tune_index = rs6000_tune_index;
+    }
   else if (cpu_index >= 0)
-    rs6000_tune_index = tune_index = cpu_index;
+    {
+      enum processor_type cur_cpu
+	= processor_target_table[cpu_index].processor;
+
+      rs6000_tune_index = tune_index
+	= (cur_cpu == PROCESSOR_FUTURE
+	   ? rs6000_cpu_name_lookup ("power10")
+	   : cpu_index);
+    }
   else
     {
       size_t i;
       enum processor_type tune_proc
 	= (TARGET_POWERPC64 ? PROCESSOR_DEFAULT64 : PROCESSOR_DEFAULT);
 
+      if (tune_proc == PROCESSOR_FUTURE)
+	tune_proc = PROCESSOR_POWER10;
+
       tune_index = -1;
       for (i = 0; i < ARRAY_SIZE (processor_target_table); i++)
 	if (processor_target_table[i].processor == tune_proc)