combine.c (make_extraction): Check TRULY_NOOP_TRUNCATION before creating LHS paradoxical subregs.

	* combine.c (make_extraction): Check TRULY_NOOP_TRUNCATION before
	creating LHS paradoxical subregs.  Fix surrounding returns to
	use NULL_RTX rather than 0.

From-SVN: r149401

gcc/ChangeLog

+2009-07-08  Adam Nemet  <anemet@caviumnetworks.com>
+
+	* combine.c (make_extraction): Check TRULY_NOOP_TRUNCATION before
+	creating LHS paradoxical subregs.  Fix surrounding returns to
+	use NULL_RTX rather than 0.
+
 2009-07-08  DJ Delorie  <dj@redhat.com>
 
 	* config/mep/mep.c: (mep_option_can_inline_p): New.

gcc/combine.c

@@ -6692,18 +6692,25 @@ make_extraction (enum machine_mode mode, rtx inner, HOST_WIDE_INT pos,
       inner = adjust_address_nv (inner, wanted_inner_mode, offset);
     }
 
-  /* If INNER is not memory, we can always get it into the proper mode.  If we
-     are changing its mode, POS must be a constant and smaller than the size
-     of the new mode.  */
+  /* If INNER is not memory, get it into the proper mode.  If we are changing
+     its mode, POS must be a constant and smaller than the size of the new
+     mode.  */
   else if (!MEM_P (inner))
     {
+      /* On the LHS, don't create paradoxical subregs implicitely truncating
+	 the register unless TRULY_NOOP_TRUNCATION.  */
+      if (in_dest
+	  && !TRULY_NOOP_TRUNCATION (GET_MODE_BITSIZE (GET_MODE (inner)),
+				     GET_MODE_BITSIZE (wanted_inner_mode)))
+	return NULL_RTX;
+
       if (GET_MODE (inner) != wanted_inner_mode
 	  && (pos_rtx != 0
 	      || orig_pos + len > GET_MODE_BITSIZE (wanted_inner_mode)))
-	return 0;
+	return NULL_RTX;
 
       if (orig_pos < 0)
-	return 0;
+	return NULL_RTX;
 
       inner = force_to_mode (inner, wanted_inner_mode,
 			     pos_rtx