Use scalar_mode in expand_shift_1

Since this function handles scalar and vector shifts:

  machine_mode scalar_mode = mode;
  if (VECTOR_MODE_P (mode))
    scalar_mode = GET_MODE_INNER (mode);

is equivalent to:

  scalar_mode = GET_MODE_INNER (mode);

2017-10-23  Richard Sandiford  <richard.sandiford@linaro.org>
	    Alan Hayward  <alan.hayward@arm.com>
	    David Sherwood  <david.sherwood@arm.com>

gcc/
	* expmed.c (expand_shift_1): Use scalar_mode for scalar_mode.

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

From-SVN: r253999

gcc/ChangeLog

+2017-10-23  Richard Sandiford  <richard.sandiford@linaro.org>
+	    Alan Hayward  <alan.hayward@arm.com>
+	    David Sherwood  <david.sherwood@arm.com>
+
+	* expmed.c (expand_shift_1): Use scalar_mode for scalar_mode.
+
 2017-10-23  Richard Biener  <rguenther@suse.de>
 
 	PR tree-optimization/82129

gcc/expmed.c

@@ -2337,12 +2337,10 @@ expand_shift_1 (enum tree_code code, machine_mode mode, rtx shifted,
   optab lrotate_optab = rotl_optab;
   optab rrotate_optab = rotr_optab;
   machine_mode op1_mode;
-  machine_mode scalar_mode = mode;
+  scalar_mode scalar_mode = GET_MODE_INNER (mode);
   int attempt;
   bool speed = optimize_insn_for_speed_p ();
 
-  if (VECTOR_MODE_P (mode))
-    scalar_mode = GET_MODE_INNER (mode);
   op1 = amount;
   op1_mode = GET_MODE (op1);