}
}
+/* See if there is a more optimal way to implement the operation "*MEM CODE VAL"
+ using memory order MODEL. If AFTER is true the operation needs to return
+ the value of *MEM after the operation, otherwise the previous value.
+ TARGET is an optional place to place the result. The result is unused if
+ it is const0_rtx.
+ Return the result if there is a better sequence, otherwise NULL_RTX. */
+
+static rtx
+maybe_optimize_fetch_op (rtx target, rtx mem, rtx val, enum rtx_code code,
+ enum memmodel model, bool after)
+{
+ /* If the value is prefetched, or not used, it may be possible to replace
+ the sequence with a native exchange operation. */
+ if (!after || target == const0_rtx)
+ {
+ /* fetch_and (&x, 0, m) can be replaced with exchange (&x, 0, m). */
+ if (code == AND && val == const0_rtx)
+ {
+ if (target == const0_rtx)
+ target = gen_reg_rtx (GET_MODE (mem));
+ return maybe_emit_atomic_exchange (target, mem, val, model);
+ }
+
+ /* fetch_or (&x, -1, m) can be replaced with exchange (&x, -1, m). */
+ if (code == IOR && val == constm1_rtx)
+ {
+ if (target == const0_rtx)
+ target = gen_reg_rtx (GET_MODE (mem));
+ return maybe_emit_atomic_exchange (target, mem, val, model);
+ }
+ }
+
+ return NULL_RTX;
+}
+
/* Try to emit an instruction for a specific operation varaition.
OPTAB contains the OP functions.
TARGET is an optional place to return the result. const0_rtx means unused.
get_atomic_op_for_code (&optab, code);
+ /* Check to see if there are any better instructions. */
+ result = maybe_optimize_fetch_op (target, mem, val, code, model, after);
+ if (result)
+ return result;
+
/* Check for the case where the result isn't used and try those patterns. */
if (unused_result)
{