re PR target/62662 (Miscompilation of Qt on s390x)

2014-09-19  Andreas Krebbel  <Andreas.Krebbel@de.ibm.com>

	PR target/62662
	* config/s390/s390.c (s390_emit_epilogue): When doing the return
	address load optimization force s390_optimize_prologue to leave it
	that way.  Only do the optimization if we already decided to push
	r14 into a stack slot.

From-SVN: r215381

gcc/ChangeLog

+2014-09-19  Andreas Krebbel  <Andreas.Krebbel@de.ibm.com>
+
+	PR target/62662
+	* config/s390/s390.c (s390_emit_epilogue): When doing the return
+	address load optimization force s390_optimize_prologue to leave it
+	that way.  Only do the optimization if we already decided to push
+	r14 into a stack slot.
+
 2014-09-19  Marat Zakirov  <m.zakirov@samsung.com>
 
 	* asan.c (build_check_stmt): Alignment arg was added.

gcc/config/s390/s390.c

@@ -9083,11 +9083,14 @@ s390_emit_epilogue (bool sibcall)
       if (! sibcall)
 	{
 	  /* Fetch return address from stack before load multiple,
-	     this will do good for scheduling.  */
-
-	  if (cfun_frame_layout.save_return_addr_p
-	      || (cfun_frame_layout.first_restore_gpr < BASE_REGNUM
-		  && cfun_frame_layout.last_restore_gpr > RETURN_REGNUM))
+	     this will do good for scheduling.
+
+	     Only do this if we already decided that r14 needs to be
+	     saved to a stack slot. (And not just because r14 happens to
+	     be in between two GPRs which need saving.)  Otherwise it
+	     would be difficult to take that decision back in
+	     s390_optimize_prologue.  */
+	  if (cfun_gpr_save_slot (RETURN_REGNUM) == -1)
 	    {
 	      int return_regnum = find_unused_clobbered_reg();
 	      if (!return_regnum)
@@ -9102,6 +9105,13 @@ s390_emit_epilogue (bool sibcall)
 	      addr = gen_rtx_MEM (Pmode, addr);
 	      set_mem_alias_set (addr, get_frame_alias_set ());
 	      emit_move_insn (return_reg, addr);
+
+	      /* Once we did that optimization we have to make sure
+		 s390_optimize_prologue does not try to remove the
+		 store of r14 since we will not be able to find the
+		 load issued here.  */
+	      cfun_frame_layout.save_return_addr_p = true;
+	      cfun_gpr_save_slot (RETURN_REGNUM) = -1;
 	    }
 	}