dce: Don't dead-code delete separately wrapped restores

If there is a separately wrapped register restore on some path that
is dead (say, control goes into an endless loop after it), then we
cannot delete that restore because that would confuse the DWARF CFI
(if there is another path joining).
This happens with gcc.dg/torture/pr53168.c, for example.


	* dce.c (delete_unmarked_insns): Don't delete instructions with
	a REG_CFA_RESTORE note.

From-SVN: r241060

gcc/ChangeLog

 2016-10-12  Segher Boessenkool  <segher@kernel.crashing.org>
 
+	* dce.c (delete_unmarked_insns): Don't delete instructions with
+	a REG_CFA_RESTORE note.
+
+2016-10-12  Segher Boessenkool  <segher@kernel.crashing.org>
+
 	* common.opt (-fshrink-wrap-separate): New flag.
 	* doc/invoke.texi: Document it.
 	* doc/tm.texi.in (Shrink-wrapping separate components): New subsection.

gcc/dce.c

@@ -587,6 +587,15 @@ delete_unmarked_insns (void)
 	  if (!dbg_cnt (dce))
 	    continue;
 
+	  if (crtl->shrink_wrapped_separate
+	      && find_reg_note (insn, REG_CFA_RESTORE, NULL))
+	    {
+	      if (dump_file)
+		fprintf (dump_file, "DCE: NOT deleting insn %d, it's a "
+				    "callee-save restore\n", INSN_UID (insn));
+	      continue;
+	    }
+
 	  if (dump_file)
 	    fprintf (dump_file, "DCE: Deleting insn %d\n", INSN_UID (insn));