rs6000 - Fix PR target/88343

The PR is about unnecessary saves of the pic base register, it shows on m32 Linux and m32/m64 Darwin.

The fix is to check that we are in a pic mode and that the picbase has actually been used.
As a bonus, some #ifdef’d TARGET_MACHO code is no longer required.

2018-12-12 Segher Boessenkool  <segher@kernel.crashing.org>
	   Iain Sandoe  <iain@sandoe.co.uk>

	PR target/88343
	* config/rs6000/rs6000.c (save_reg_p): Do not save the picbase reg
	unless it has been used.
	(first_reg_to_save): Remove dead code.


Co-Authored-By: Iain Sandoe <iain@sandoe.co.uk>

From-SVN: r267049

gcc/ChangeLog

+2018-12-12 Segher Boessenkool  <segher@kernel.crashing.org>
+	   Iain Sandoe  <iain@sandoe.co.uk>
+
+	PR target/88343
+	* config/rs6000/rs6000.c (save_reg_p): Do not save the picbase reg
+	unless it has been used.
+	(first_reg_to_save): Remove dead code.
+
 2018-12-12  Iain Sandoe  <iain@sandoe.co.uk>
 
 	* config/rs6000/rs6000-protos.h (rs6000_call_darwin): New.

gcc/config/rs6000/rs6000.c

@@ -23969,7 +23969,7 @@ save_reg_p (int reg)
 	return true;
 
       if ((DEFAULT_ABI == ABI_V4 || DEFAULT_ABI == ABI_DARWIN)
-	  && flag_pic)
+	  && flag_pic && crtl->uses_pic_offset_table)
 	return true;
     }
 
@@ -23989,13 +23989,6 @@ first_reg_to_save (void)
     if (save_reg_p (first_reg))
       break;
 
-#if TARGET_MACHO
-  if (flag_pic
-      && crtl->uses_pic_offset_table
-      && first_reg > RS6000_PIC_OFFSET_TABLE_REGNUM)
-    return RS6000_PIC_OFFSET_TABLE_REGNUM;
-#endif
-
   return first_reg;
 }