CS 573

Homework 1

Due Friday, February 13, 2004

1. Consider the following sequence of C code:

   a = b * 2;
   c = a * 4;
   b = b - d;
   if (a < b)
       d = c + 5;
   else
       d = b - 4;
   

   Generate optimal pseudo-assembly code (in the sense of executing as quickly as possible) for (1) an Alpha and (2) an IA-64-style style computer, assuming:

   • Every variable is in a register (not memory).
   • Every register is initially valid.
   • Every instruction takes the same amount of time in the pipelines.
   • You are able to execute an arbitrary number of instructions simultaneously (subject to dependencies, of course).

   In the case of IA-64, you may also assume:

   • All instructions denoted as starting simultaneously read their registers, perform their operations, and then write their registers, including predicate registers.
   • You are able to use predicated instructions to replace if then else statements.

2. Write a one-page paper comparing the Alpha to the IA-64 approaches to developing a 64-bit architecture while maintaining an existing customer base.