combine: Don't call extract_left_shift with count < 0 (PR67483)

If the compiled program does a shift by a negative amount, combine will
happily work with that, but it shouldn't then do an undefined operation
in GCC itself.  This patch fixes the first case mentioned in the bug
report (I haven't been able to reproduce the second case, on trunk at
least).


	PR rtl-optimization/67483
	* combine.c (make_compound_operation): Don't call extract_left_shift
	with negative shift amounts.

From-SVN: r236232

gcc/ChangeLog

+2016-05-13  Segher Boessenkool  <segher@kernel.crashing.org>
+
+	PR rtl-optimization/67483
+	* combine.c (make_compound_operation): Don't call extract_left_shift
+	with negative shift amounts.
+
 2016-05-13  Jakub Jelinek  <jakub@redhat.com>
 
 	PR bootstrap/71071

gcc/combine.c

@@ -8037,6 +8037,7 @@ make_compound_operation (rtx x, enum rtx_code in_code)
 	  && ! (GET_CODE (lhs) == SUBREG
 		&& (OBJECT_P (SUBREG_REG (lhs))))
 	  && CONST_INT_P (rhs)
+	  && INTVAL (rhs) >= 0
 	  && INTVAL (rhs) < HOST_BITS_PER_WIDE_INT
 	  && INTVAL (rhs) < mode_width
 	  && (new_rtx = extract_left_shift (lhs, INTVAL (rhs))) != 0)