1. The Last Lecture COMP 512 Rice University Houston, Texas Fall 2003
Copyright 2003, Keith D. Cooper & Linda Torczon, all rights reserved.
Students enrolled in Comp 512 at Rice University have explicit permission to make copies of these materials for their personal use.

2. Putting It All Together
Key questions that a compiler writer must answer?
What should the optimizer & back end do?
How should the compiler represent the program?
Broad answers
Figure out what the real problems are
Learn everything you can about the target machine
Attack each problem with a specific plan
Separate concerns as long as possible
COMP 512, Fall 2003

3. Lessons Experience is a tough teacher
Understand what the code looks like
On input to the compiler and on output from the compiler
Hard to see problems in large procedures
A good compiler need not do everything
Study the code & figure out what’s needed
Do those things well & do them thoroughly
Hand simulation before implementation pays off
Avoid implementing things that solve no problem
Find the right level of abstraction for each optimization
Constant propagation can be done at source level
Redundancy elimination should be done at a low-level
COMP 512, Fall 2003

4. Lessons Experience is a tough teacher
Intermediate representations are important
Determines level of exposed detail
Every pass traverses it, so efficient manipulation is critical
Code shape and name spaces are important
Determine opportunities & size of data structures
Has large impact on effectiveness of algorithms
Compile-time space counts
Limits size of procedures that can be compiled
Compiler touches all that space
More complex analyses take lots of space
COMP 512, Fall 2003

5. { Lessons Experience is a tough teacher
Separation of concerns is vital to progress
Resource constraints from rearrangement
Allocation from optimization
Parsing from code generation
Separation of concerns interferes with optimization
Allocation & scheduling
Evaluation order & redundancy elimination
Code shape decisions affect later passes {
Loop shape, case stmts.
Annotations (ILOC tags)
COMP 512, Fall 2003

6. And that’s the end of our story ...
Comp 512
And that’s the end of our story ...
COMP 512, Fall 2003