[RS6000] Stop regrename twiddling with split-stack prologue

	PR target/70947
	* config/rs6000/rs6000.c (rs6000_expand_split_stack_prologue): Stop
	regrename modifying insns saving lr before __morestack call.
	* config/rs6000/rs6000.md (split_stack_return): Similarly for
	insns restoring lr after __morestack call.

From-SVN: r236052

gcc/ChangeLog

+2016-05-10  Alan Modra  <amodra@gmail.com>
+
+	PR target/70947
+	* config/rs6000/rs6000.c (rs6000_expand_split_stack_prologue): Stop
+	regrename modifying insns saving lr before __morestack call.
+	* config/rs6000/rs6000.md (split_stack_return): Similarly for
+	insns restoring lr after __morestack call.
+
 2016-05-09  Jakub Jelinek  <jakub@redhat.com>
 
 	* config/i386/i386.md (set_got, set_got_labelled, lwp_llwpcb,

gcc/config/rs6000/rs6000.c

@@ -27993,6 +27993,11 @@ rs6000_expand_split_stack_prologue (void)
 				   const0_rtx, const0_rtx));
   call_fusage = NULL_RTX;
   use_reg (&call_fusage, r12);
+  /* Say the call uses r0, even though it doesn't, to stop regrename
+     from twiddling with the insns saving lr, trashing args for cfun.
+     The insns restoring lr are similarly protected by making
+     split_stack_return use r0.  */
+  use_reg (&call_fusage, r0);
   add_function_usage_to (insn, call_fusage);
   emit_insn (gen_frame_load (r0, r1, info->lr_save_offset));
   insn = emit_move_insn (lr, r0);

gcc/config/rs6000/rs6000.md

@@ -12587,8 +12587,10 @@
    (set_attr "indexed" "no")])
 
 ;; A return instruction which the middle-end doesn't see.
+;; Use r0 to stop regrename twiddling with lr restore insns emitted
+;; after the call to __morestack.
 (define_insn "split_stack_return"
-  [(unspec_volatile [(const_int 0)] UNSPECV_SPLIT_STACK_RETURN)]
+  [(unspec_volatile [(use (reg:SI 0))] UNSPECV_SPLIT_STACK_RETURN)]
   ""
   "blr"
   [(set_attr "type" "jmpreg")])