Pointer and Shape Analysis Seminar http://www.cs.tau.ac.il/~msagiv/courses/shape.html

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Pointer and Shape Analysis Seminarhttp//www.cs.t
au.ac.il/msagiv/courses/shape.html

• Mooly Sagiv
• Schriber 317
• msagiv_at_post
• Office Hours Thursday 15-16

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Outline

1. General information
2. Seminar subject
3. How to give a presentation

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General Information

• Prerequisites
• Compilers Program Analysis
• Select 3 topics by Sunday
• Participate in 9 seminar talks
• Present a paper

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Tentative Schedule

• Today Intro
• Sunday (selection of topic)
• Student lectures

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Pointer and Shape Analysis
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Program Analysis

• Statically analyze the program text (w/o input)
• Determine conservative information about all
  (some) program executions
• Applications
• Verification
• Each verified property holds but not all
  properties can be verified all programs
• False alarms
• Compiler optimizations
• Parallelizations
• Garbage collection

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Alias Analysis

• Two expressions referring to the same memory
  location at a given program point on some (all)
  executions

1 p a 2 q b 3 if (getc()) 4
q c 5
q ? b
p ? a
q ? c
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Points-To Analysis

• Determine if a variable points to a variable at
  some (all) execution paths

1 p a 2 q b 3 if (getc()) 4
q c 5
q ?? b
p ?? a
q ?? c
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Shape Analysis

• Determine the potential shapes of memory at a
  given program point

1 p a 2 q b 3 if (getc()) 4
q c
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Applications

• Adapt other optimizations
• Constant propagationx 5p 7 x
• Side-effect analysis p q t
• Verification
• No null dereferences
• No memory leaks

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Iterative Program Analysis

• Start by optimistically assuming that nothing is
  wrong
• No aliases
• No points-to set
• Empty sets of shape graphs
• At every iteration apply the abstract meaning of
  programming language statements and add more
  aliases/points-to/shape graphs
• Stop when no changes occur

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Iterative Points-to Analysis
t a
t?a
y b
t?a, y?b
z c
t?a, y?b, z ?c
p t
t?a, y?b, z ?c
t?a, y?b, z ?c
p y
p z
t?a, y?b, z ?c, p?y
t?a, y?b, z ?c, p?z
t?a, y?b, z ?c, p?y, p?z
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Iterative Points-to Analysis
t a
t?a
y b
t?a, y?b
z c
t?a, y?b, z ?c, p?y, p?z
p t
t?a, y?b, z ?c, p?y, p?z, y?a, z?a
t?a, y?b, z ?c, p?y, p?z, y?a, z?a
p y
p z
t?a, y?b, z ?c, p?y
t?a, y?b, z ?c, p?z
t?a, y?b, z ?c, p?y, p?z
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Iterative Points-to Analysis
t a
t?a
y b
t?a, y?b
z c
t?a, y?b, z ?c, p?y, p?z
p t
t?a, y?b, z ?c, p?y, p?z, y?a, z?a
t?a, y?b, z ?c, p?y, p?z, y?a, z?a
p y
p z
t?a, y?b, z ?c, p?y, y?a, z?a
t?a, y?b, z ?c, p?z, y?a, z?a
t?a, y?b, z ?c, p?y, p?z
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Iterative Points-to Analysis
t a
t?a
y b
t?a, y?b
z c
t?a, y?b, z ?c, p?y, p?z, y?a, z?a
p t
t?a, y?b, z ?c, p?y, p?z, y?a, z?a
t?a, y?b, z ?c, p?y, p?z, y?a, z?a
p y
p z
t?a, y?b, z ?c, p?y, y?a, z?a
t?a, y?b, z ?c, p?z, y?a, z?a
t?a, y?b, z ?c, p?y, p?z, y?a, z?a
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Iterative Shape Analysis
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Soundness

• Every alias is detected
• Every points-to fact is detected
• Every potential shape is detected
• Every potential bug is detected
• Every enabled optimization is correct

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Dimensions of program analysis

• Flow sensitive
• Context sensitive

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Material on Pointer Analysis

• Alias Analysis
• Points-to Analysis
• Shape Analysis
• Applications

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Giving a presentation

• Ian Parbery

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How to give a presentation

• What to say and how to say it
• Getting through the audience
• Visual aids

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What to say and how to say it

• Communicate the Key Ideas
• Dont get bogged down in Details
• The best talk make you read the paper
• Structure your talk
• Use Top-Down approach
• Introduction
• Body
• Technicalities
• The Conclusion

Use Examples
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Introduction

• Define the problem
• Motivate the audience
• Introduce terminology
• Discuss earlier work
• Emphasize the contributions
• Provide a road map

Use Examples
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The body

• Abstract the major results
• Explain the significance of the results
• Explain the main techniques
• Use enlightening examples
• Demonstrations are welcome

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Technicalities

• Expert only part
• Show something really interesting beyond the
  paper/tool

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The Conclusion

• Hindsight is clearer than Foresight
• Give open problems/further work
• Indicate that your talk is over

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Know your audience

• Background

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Getting through the Audience

• Use Repetitions
• Remind, dont assume
• Dont over-run
• Maintain Eye Contact
• Control your voice
• Control your motion
• Take care of your appearance

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Visual Aids

• PowerPoint transparencies
• Dont overload transparencies
• Dont use too many transparencies
• Use Overlays Properly
• Use Color Effectively
• Use Pictures and Tables
• The blackboard can be used too

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Dont overload transparencies

• The input of the program can be arbitrary.
• Let x be a prime number, i.e., all the numbers
  zltx do not divide x. y be the next prime number,
  i.e., etc.

• Arbitrary input
• Prime number x
• The next prime y

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Use overlays (im)properly

• Item 1
• Item 1.1
• Item 1.2
• Item 2
• Item 2.1
• Item 2.1.1

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Use colors properly

• Item 1
• Item 2
• Item 3

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The End
http//www.cs.tau.ac.il/msagiv/courses/shape.html