regcprop: Avoid REG_CFA_REGISTER notes (PR85645)

Changing a SET that has a REG_CFA_REGISTER note is wrong if we are
changing the SET_DEST, or if the REG_CFA_REGISTER has nil as its
argument, and maybe some other cases.  It's never really useful to
propagate into such an instruction, so let's just bail whenever we
see such a note.


	PR rtl-optimization/85645
	*  regcprop.c (copyprop_hardreg_forward_1): Don't propagate into an
	insn that has a REG_CFA_REGISTER note.

From-SVN: r260074

gcc/ChangeLog

+2018-05-09  Segher Boessenkool  <segher@kernel.crashing.org>
+
+	PR rtl-optimization/85645
+	*  regcprop.c (copyprop_hardreg_forward_1): Don't propagate into an
+	insn that has a REG_CFA_REGISTER note.
+
 2018-05-09  Richard Sandiford  <richard.sandiford@linaro.org>
 
 	* cfgexpand.c (expand_clobber): New function.

gcc/regcprop.c

@@ -848,6 +848,12 @@ copyprop_hardreg_forward_1 (basic_block bb, struct value_data *vd)
 		  && reg_overlap_mentioned_p (XEXP (link, 0), SET_SRC (set)))
 		set = NULL;
 	    }
+
+	  /* We need to keep CFI info correct, and the same on all paths,
+	     so we cannot normally replace the registers REG_CFA_REGISTER
+	     refers to.  Bail.  */
+	  if (REG_NOTE_KIND (link) == REG_CFA_REGISTER)
+	    goto did_replacement;
 	}
 
       /* Special-case plain move instructions, since we may well