Optimization of Assembly Language Code

Resource: As with the previous lab, you will want to refer to HP's manual, PA-RISC 1.1 Architecture and Instruction Set Reference Manual, Third Edition. This is available on-line in either html or postscript format.

Preparation: Before the laboratory session, read the C program FahrToCelsius which is found as file table.c in directory ~walker/assembly.

Steps for this Lab:

1. Focusing on this C program, compile the program to assembly to determine what code is produced using the gcc compiler.

2. The gcc compiler allows you to request one of several levels of optimization of the code, using the -O option. E.g., for level 2 optimization, type:

   
        gcc -S -O2 table.c
   
   

3. Compare the non-optimized and optimized code generated by the compiler you selected. For example, you should observe the nature of any changes between the two assembly language listings. Are registers used differently? Are some instructions omitted? Are different types of instructions used? Is one listing significantly shorter?

   Also, in addition to the above discussion, for both your non-optimized and optimized code:

   • draw a picture of the registers and show which registers are used for what purposes,
   • draw a picture of the run-time stack to show what values are stored where (relative to %r30 and/or %r3), and
   • discuss how the floating point arithmetic is handled.

1. Your work for this lab may be limited to the output from just one of the compilers mentioned. During class, we may have the chance to hear about each compiler.

2. In answering the above questions, you need not annotate the assembly language programs. In making comparisons or in discussing approaches, you may find it helpful to comment upon specific instructions or code segments, but there is no need to annotate the entire assembly language code.

Work to be turned in:

• Step 3.

This document is available on the World Wide Web as

     http://www.math.grin.edu/~walker/courses/211/labs/lab.code-optimization.html