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Recap from last time
• We saw various different issues related to
program analysis and program
transformations
• You were not expected to know all of these
things
• We will learn more about each one of the
topics we touched upon last time
Program Analyzer Issues (discuss)
Program
Input Analyzer Output
Input issues
• How much of the program do we see?
– all?
– one file at a time?
– one library at a time?
– reflection…
• Any additional inputs?
– any human help?
– profile info?
Instructor’s discussion notes Input ProgramAnalyzer Output
Analysis issues
- Analysis/compilation model
- Separate compilation/analysis • quick, but no opportunities for interprocedural analysis
- Link-time • allows interprocedural and whole program analysis
- • but what about shared precompiled libraries?and what about compile-time?
- Run-time • best optimization/analysis potential (can even use run-time state as
- additional information)can handle run-time extensions to the program
- Selective run-time compilation^ •^ but severe pressure to limit compilation time
- • choose what part of compilation to delay until run-timecan balance compile-time/benefit tradeoffs
Instructor’s discussion notes Input ProgramAnalyzer Output
Output issues
• Form of output varies widely, depending on
analysis
- alias information
- constantness information
- loop terminates/does not terminate
• Correctness of analysis results
- depends on what the results are used for
- are we attempting to design algorithsm for solving
undecidable problems?
- notion of approximation
- statistical output
Instructor’s discussion notes Input ProgramAnalyzer Output
Program Transformation Issues (discuss)
Program Input (^) Transformer Output
Transformation issues
• What is profitable?
• What order to perform transformations?
• What happens to the program
representation?
• What happens to the computed information?
For example alias information? Need to
recompute?
Instructor’s discussion notes Input (^) Transformer^ Program Output
Output issues
• Output in same IL as input?
• Should the output program behave the same
way as the input program?
Instructor’s discussion notes Input (^) Transformer^ Program Output
Ideas for generating project ideas
• If you are currently doing research
– that is related to programming
languages/compilers
– carve out some part of your current research, and
do it for the project
• Think about what annoys you the most
– in programming
– and fix it using program analysis techniques
Ideas for generating project ideas
• Think about technology trends
- iphone, mobile devices
- multicore, parallelism
- web browsers, java scripts, etc.
- bluetooth, ad-hoc networks
- how do these change the way we program/compile?
• Try to find bugs in real programs using PL
techniques
- search for “Dawson Engler” and look at some of his
papers. Try to use similar techniques to find real bugs.
Tour of common optimizations
Simple example
foo(z) { x := 3 + 6; y := x – 5 return z * y }
Another example
x := a + b; ... y := a + b;
Another example
x := a + b; ... y := a + b;
