Make more use of subreg_offset_from_lsb

This patch makes use of the subreg_offset_from_lsb function
added by an earlier patch in the SVE series.

2017-08-24  Richard Sandiford  <richard.sandiford@linaro.org>
	    Alan Hayward  <alan.hayward@arm.com>
	    David Sherwood  <david.sherwood@arm.com>

gcc/
	* combine.c (make_extraction): Use subreg_offset_from_lsb.

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

From-SVN: r251326

gcc/ChangeLog

+2017-08-24  Richard Sandiford  <richard.sandiford@linaro.org>
+	    Alan Hayward  <alan.hayward@arm.com>
+	    David Sherwood  <david.sherwood@arm.com>
+
+	* combine.c (make_extraction): Use subreg_offset_from_lsb.
+
 2017-08-23  Daniel Santos  <daniel.santos@pobox.com>
 
 	* config/i386/i386.h (ix86_frame::stack_realign_allocate_offset):

gcc/combine.c

@@ -7488,26 +7488,15 @@ make_extraction (machine_mode mode, rtx inner, HOST_WIDE_INT pos,
 		 return a new hard register.  */
 	      if (pos || in_dest)
 		{
-		  HOST_WIDE_INT final_word = pos / BITS_PER_WORD;
-
-		  if (WORDS_BIG_ENDIAN
-		      && GET_MODE_SIZE (inner_mode) > UNITS_PER_WORD)
-		    final_word = ((GET_MODE_SIZE (inner_mode)
-				   - GET_MODE_SIZE (tmode))
-				  / UNITS_PER_WORD) - final_word;
-
-		  final_word *= UNITS_PER_WORD;
-		  if (BYTES_BIG_ENDIAN &&
-		      GET_MODE_SIZE (inner_mode) > GET_MODE_SIZE (tmode))
-		    final_word += (GET_MODE_SIZE (inner_mode)
-				   - GET_MODE_SIZE (tmode)) % UNITS_PER_WORD;
+		  unsigned int offset
+		    = subreg_offset_from_lsb (tmode, inner_mode, pos);
 
 		  /* Avoid creating invalid subregs, for example when
 		     simplifying (x>>32)&255.  */
-		  if (!validate_subreg (tmode, inner_mode, inner, final_word))
+		  if (!validate_subreg (tmode, inner_mode, inner, offset))
 		    return NULL_RTX;
 
-		  new_rtx = gen_rtx_SUBREG (tmode, inner, final_word);
+		  new_rtx = gen_rtx_SUBREG (tmode, inner, offset);
 		}
 	      else
 		new_rtx = gen_lowpart (tmode, inner);