C2 currently generates code like

  0x000003ff9d3e8920: ldr w11, [x1,#16]
  0x000003ff9d3e8924: lsl x10, x11, #3
  0x000003ff9d3e8928: cbnz x10, 0x000003ff9d3e8950

when doing a pointer comparison against 0

The lsl instruction is generated by a DecodeN node which can be elided in this case.

The following is a simple test case

public class decode {
    public static void main(String[] args) {
        if (args[0] != null) {
System.out.println("not null");
}
    }
}

run as follows

/home/ed/jdk9-dev/hs-comp/build/linux-aarch64-normal-server-fastdebug/images/jdk/bin/java -XX:-TieredCompilation -Xcomp -XX:CompileOnly=decode::main -XX:+UnlockDiagnosticVMOptions -XX:+PrintAssembly -XX:+PrintOptoAssembly -XX:+PrintIdeal decode