Add copy_rtx call to RTL loop unroller

This is needed if the step is an unshared constant, like many
(const ...)s are.  Without this patch, libgfortran would fail
to build for SVE.

2017-09-21  Richard Sandiford  <richard.sandiford@linaro.org>
	    Alan Hayward  <alan.hayward@arm.com>
	    David Sherwood  <david.sherwood@arm.com>

gcc/
	* loop-unroll.c (split_iv): Call copy_rtx on the step.

Co-Authored-By: Alan Hayward <alan.hayward@arm.com>
Co-Authored-By: David Sherwood <david.sherwood@arm.com>

From-SVN: r253058

gcc/ChangeLog

@@ -2,6 +2,12 @@
 	    Alan Hayward  <alan.hayward@arm.com>
 	    David Sherwood  <david.sherwood@arm.com>
 
+	* loop-unroll.c (split_iv): Call copy_rtx on the step.
+
+2017-09-21  Richard Sandiford  <richard.sandiford@linaro.org>
+	    Alan Hayward  <alan.hayward@arm.com>
+	    David Sherwood  <david.sherwood@arm.com>
+
 	* tree.c (find_atomic_core_type): Check tree_fits_uhwi_p before
 	calling tree_to_uhwi.
 

gcc/loop-unroll.c

@@ -1731,7 +1731,8 @@ split_iv (struct iv_to_split *ivts, rtx_insn *insn, unsigned delta)
   else
     {
       incr = simplify_gen_binary (MULT, mode,
-				  ivts->step, gen_int_mode (delta, mode));
+				  copy_rtx (ivts->step),
+				  gen_int_mode (delta, mode));
       expr = simplify_gen_binary (PLUS, GET_MODE (ivts->base_var),
 				  ivts->base_var, incr);
     }