tcg: Optimize half-dead add2/sub2 When x86_64 guest is not in 64-bit mode, the high-part of the 64-bit add is dead. When the host is 32-bit, we can simplify to 32-bit arithmetic. Signed-off-by: Richard Henderson <rth@twiddle.net> Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>