HW3: Superscalar In Practice

CS 641 Homework, Dr. Lawlor

1.) Here's a snippet of x86 assembly code. List all the RAW, WAR, and WAW dependencies between all instructions (don't include the implicit EFLAGS dependencies):

1:	mov eax,17
2:	imul eax,ebx
3:	mov DWORD[ecx],eax
4:	mov eax,21
5:	add ecx,eax

2.) Now manually rename the registers above to eliminate all but the RAW dependencies.

3.) Write an "instructions_interlock" function for the UEMU emulator to detect when the next two instructions can't be run simultaniously. Remember, you can't run two instructions simultaniously if:

Either instruction throws an exception (0xE... instructions, in UEMU)
The first instruction is a branch instruction (writes to register 0xF in UEMU)
The second instruction depends on a value computed by the first

Your "instructions_interlock" function should return correct results for any pair of instructions, but here are two tiny sample UEMU programs for testing:

3a_add.txt takes 5 clocks without superscalar execution, but should take 4 clocks with superscalar execution. There are several opportunities for read-after-write dependencies. The only other hazard is the emulator exit, the last instruction.
3b_loop.txt takes 27 clocks without superscalar execution, but should take just 21 clocks when totally superscalar. There are several branch hazards, and emulator exception calls.

Download the uemu_superscalar.cpp source code. It takes the input program from standard input, so you'll need to run it like "my_uemu.exe < 3a_add.txt" on the command line.

This assignment is due by midnight on Thursday, February 21. Send me a text file with your dependencies and renamed assembly code, and your modified uemu_superscalar.cpp, attached to an email.