Tighten condition for converting SUBREG reloads from OP_OUT to OP_INOUT

gcc/
	PR target/78660
	* lra-constraints.c (curr_insn_transform): Tighten condition
	for converting SUBREG reloads from OP_OUT to OP_INOUT.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@245599 138bc75d-0d04-0410-961f-82ee72b054a4

gcc/ChangeLog

@@ -1,3 +1,9 @@
+2017-02-20  Matthew Fortune  <matthew.fortune@imgtec.com>
+
+	PR target/78660
+	* lra-constraints.c (curr_insn_transform): Tighten condition
+	for converting SUBREG reloads from OP_OUT to OP_INOUT.
+
 2017-02-20  Matthew Fortune  <matthew.fortune@imgtec.com>
 
 	PR target/78660

gcc/lra-constraints.c

@@ -4140,7 +4140,17 @@ curr_insn_transform (bool check_only_p)
 			  < GET_MODE_PRECISION (GET_MODE (reg))
 			  && WORD_REGISTER_OPERATIONS)))
 		{
-		  if (type == OP_OUT)
+		  /* An OP_INOUT is required when reloading a subreg of a
+		     mode wider than a word to ensure that data beyond the
+		     word being reloaded is preserved.  Also automatically
+		     ensure that strict_low_part reloads are made into
+		     OP_INOUT which should already be true from the backend
+		     constraints.  */
+		  if (type == OP_OUT
+		      && (curr_static_id->operand[i].strict_low
+			  || (GET_MODE_SIZE (GET_MODE (reg)) > UNITS_PER_WORD
+			      && (GET_MODE_SIZE (mode)
+				  < GET_MODE_SIZE (GET_MODE (reg))))))
 		    type = OP_INOUT;
 		  loc = &SUBREG_REG (*loc);
 		  mode = GET_MODE (*loc);