What is the test for determining whether defense counsel was ineffective for not moving to reduce the sentence on constitutional grounds?

In the alternative, defendant contends defense counsel was ineffective for not moving to reduce his sentence on constitutional grounds. To prove ineffective assistance, defendant must show that defense counsel's performance fell below an objective standard of reasonableness under prevailing professional norms, and that, in the absence of counsel's failure, it is reasonably probable that the result of the sentencing proceeding would have been different. (Strickland v. Washington (1984) 466 U.S. 668, 687, 694.)