combine: Handle aborts in is_parallel_of_n_reg_sets (PR68381)

Some users of is_parallel_of_n_reg_sets disregard the clobbers in a
parallel after it has returned "yes, this is a parallel of N sets and
maybe some clobbers".  But combine uses a clobber of const0_rtx to
indicate substitution failure, so this leads to disaster.

Fix this by checking for such special clobbers in is_parallel_of_n_reg_sets.


	PR rtl-optimization/68381
	* combine.c (is_parallel_of_n_reg_sets): Return false if the pattern
	is poisoned.

From-SVN: r230786

gcc/ChangeLog

+2015-11-24  Segher Boessenkool  <segher@kernel.crashing.org>
+
+	PR rtl-optimization/68381
+	* combine.c (is_parallel_of_n_reg_sets): Return false if the pattern
+	is poisoned.
+
 2015-11-23  Nick Clifton  <nickc@redhat.com>
 	    Jeff Law  <law@redhat.com>
 

gcc/combine.c

@@ -2512,7 +2512,8 @@ is_parallel_of_n_reg_sets (rtx pat, int n)
 	|| !REG_P (SET_DEST (XVECEXP (pat, 0, i))))
       return false;
   for ( ; i < len; i++)
-    if (GET_CODE (XVECEXP (pat, 0, i)) != CLOBBER)
+    if (GET_CODE (XVECEXP (pat, 0, i)) != CLOBBER
+	|| XEXP (XVECEXP (pat, 0, i), 0) == const0_rtx)
       return false;
 
   return true;