bridge: multicast: work around clang bug

Clang-10 and clang-11 run into a corner case of the register
allocator on 32-bit ARM, leading to excessive stack usage from
register spilling:

net/bridge/br_multicast.c:2422:6: error: stack frame size of 1472 bytes in function 'br_multicast_get_stats' [-Werror,-Wframe-larger-than=]

Work around this by marking one of the internal functions as
noinline_for_stack.

Link: https://bugs.llvm.org/show_bug.cgi?id=45802#c9
Signed-off-by: Arnd Bergmann <[email protected]>
Signed-off-by: David S. Miller <[email protected]>

Author: arndb

net/bridge/br_multicast.c

@@ -2413,7 +2413,8 @@ void br_multicast_uninit_stats(struct net_bridge *br)
 	free_percpu(br->mcast_stats);
 }
 
-static void mcast_stats_add_dir(u64 *dst, u64 *src)
+/* noinline for https://bugs.llvm.org/show_bug.cgi?id=45802#c9 */
+static noinline_for_stack void mcast_stats_add_dir(u64 *dst, u64 *src)
 {
 	dst[BR_MCAST_DIR_RX] += src[BR_MCAST_DIR_RX];
 	dst[BR_MCAST_DIR_TX] += src[BR_MCAST_DIR_TX];