Late Data Layout - OOPLSA Talk

Late Data Layout talk at the OOPLSA research conference (Object-Oriented Programming, Systems, Languages & Applications). Website: http://2014.splashcon.org/event/oopsla2014-unifying-data-representation-transformations

Project website: http://scala-ldl.org

Transcript

1. scala-ldl.org
   Late Data Layout:
   Unifying Data Representation Transformations
   Vlad Ureche Eugene Burmako Martin Odersky
   École polytechnique fédérale de Lausanne, Switzerland
   {first.last}@epfl.ch
   23rd of October 2014
   OOPSLA '14
   Portland, OR
   

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2. scala-ldl.org
   Late Data Layout:
   Unifying Data Representation Transformations
   

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3. scala-ldl.org
   Late Data Layout:
   Unifying Data Representation Transformations
   ●
   compiler transformations
   ●
   separate compilation
   ●
   global scope
   

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4. scala-ldl.org
   Late Data Layout:
   Unifying Data Representation Transformations
   ●
   unboxing, value classes
   ●
   how data is represented
   

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5. scala-ldl.org
   Late Data Layout:
   Unifying Data Representation Transformations
   ●
   what is there to unify?
   ●
   why bother?
   

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6. scala-ldl.org
   Motivation
   Transformation
   Conclusion
   Properties
   Benchmarks
   

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7. scala-ldl.org
   Representation Transformations
   

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8. scala-ldl.org
   Unboxing Primitive Types
   Representation Transformations
   

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9. scala-ldl.org
   Unboxing Primitive Types
   Unboxing Primitive Types
   

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10. scala-ldl.org
    Unboxing Primitive Types
    Unboxing Primitive Types
    int
    ●
    value
    ●
    no garbage collection
    ●
    locality
    

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11. scala-ldl.org
    Unboxing Primitive Types
    Unboxing Primitive Types
    ●
    indirect access
    ●
    object allocation
    ●
    and thus garbage collection
    ●
    no locality guarantees
    ●
    compatible with erased generics
    java.lang.Integer
    int
    ●
    value
    ●
    no garbage collection
    ●
    locality
    

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12. scala-ldl.org
    Unboxing Primitive Types
    Unboxing Primitive Types
    ●
    indirect access
    ●
    object allocation
    ●
    and thus garbage collection
    ●
    no locality guarantees
    ●
    compatible with erased generics
    java.lang.Integer
    in Java, programmers are
    responsible for the choice
    of representation
    int
    ●
    value
    ●
    no garbage collection
    ●
    locality
    

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13. scala-ldl.org
    Unboxing Primitive Types
    Unboxing Primitive Types
    ●
    indirect access
    ●
    object allocation
    ●
    and thus garbage collection
    ●
    no locality guarantees
    ●
    compatible with erased generics
    java.lang.Integer
    in Java, programmers are
    responsible for the choice
    of representation What about Scala?
    int
    ●
    value
    ●
    no garbage collection
    ●
    locality
    

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14. scala-ldl.org
    Unboxing Primitive Types
    Unboxing Primitive Types
    ●
    indirect access
    ●
    object allocation
    ●
    and thus garbage collection
    ●
    no locality guarantees
    ●
    compatible with erased generics
    java.lang.Integer
    int
    ●
    value
    ●
    no garbage collection
    ●
    locality
    

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15. scala-ldl.org
    Unboxing Primitive Types
    Unboxing Primitive Types
    ●
    indirect access
    ●
    object allocation
    ●
    and thus garbage collection
    ●
    no locality guarantees
    ●
    compatible with erased generics
    java.lang.Integer
    int
    ●
    value
    ●
    no garbage collection
    ●
    locality
    

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16. scala-ldl.org
    Unboxing Primitive Types
    Unboxing Primitive Types
    ●
    indirect access
    ●
    object allocation
    ●
    and thus garbage collection
    ●
    no locality guarantees
    ●
    compatible with erased generics
    java.lang.Integer
    int
    ●
    value
    ●
    no garbage collection
    ●
    locality
    scala.Int
    

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17. scala-ldl.org
    Unboxing Primitive Types
    Unboxing Primitive Types
    ●
    indirect access
    ●
    object allocation
    ●
    and thus garbage collection
    ●
    no locality guarantees
    ●
    compatible with erased generics
    java.lang.Integer
    int
    ●
    value
    ●
    no garbage collection
    ●
    locality
    scalac
    scala.Int
    

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18. scala-ldl.org
    Unboxing Primitive Types
    Unboxing Primitive Types
    ●
    indirect access
    ●
    object allocation
    ●
    and thus garbage collection
    ●
    no locality guarantees
    ●
    compatible with erased generics
    java.lang.Integer
    int
    ●
    value
    ●
    no garbage collection
    ●
    locality
    scalac
    Choice of representation
    1
    scala.Int
    

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19. scala-ldl.org
    Unboxing Primitive Types
    Unboxing Primitive Types
    ●
    indirect access
    ●
    object allocation
    ●
    and thus garbage collection
    ●
    no locality guarantees
    ●
    compatible with erased generics
    java.lang.Integer
    int
    ●
    value
    ●
    no garbage collection
    ●
    locality
    scalac
    Choice of representation
    1
    2 Coercions between representations
    scala.Int
    

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20. scala-ldl.org
    Unboxing Primitive Types
    Value Classes
    Representation Transformations
    

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21. scala-ldl.org
    Value Classes
    Value Classes
    

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22. scala-ldl.org
    Value Classes
    Value Classes
    value class
    

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23. scala-ldl.org
    Value Classes
    Value Classes
    value class
    struct (by-val)
    ●
    preferred encoding
    ●
    fields are inlined
    ●
    no heap allocations
    

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24. scala-ldl.org
    Value Classes
    Value Classes
    value class
    struct (by-val)
    ●
    preferred encoding
    ●
    fields are inlined
    ●
    no heap allocations
    ●
    fallback encoding
    ●
    compatible with
    ●
    subtyping
    ●
    erased generics
    object (by-ref)
    

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25. scala-ldl.org
    Value Classes
    Value Classes
    value class
    struct (by-val)
    ●
    preferred encoding
    ●
    fields are inlined
    ●
    no heap allocations
    ●
    fallback encoding
    ●
    compatible with
    ●
    subtyping
    ●
    erased generics
    object (by-ref)
    scalac
    Choice of representation
    1
    2 Coercions between representations
    

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26. scala-ldl.org
    Unboxing Primitive Types
    Value Classes
    Miniboxing
    Representation Transformations
    

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27. scala-ldl.org
    Miniboxing
    Miniboxing
    OOPSLA '13
    

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28. scala-ldl.org
    Miniboxing
    Miniboxing
    T (primitive)
    

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29. scala-ldl.org
    Miniboxing
    Miniboxing
    long integer
    ●
    preferred encoding
    ●
    for all primitive types
    T (primitive)
    

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30. scala-ldl.org
    Miniboxing
    Miniboxing
    long integer
    ●
    preferred encoding
    ●
    for all primitive types
    ●
    fallback encoding
    ●
    compatible with
    ●
    virtual dispatch
    ●
    subtyping
    ●
    erased generics
    T (erased to Object)
    T (primitive)
    

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31. scala-ldl.org
    Miniboxing
    Miniboxing
    long integer
    ●
    preferred encoding
    ●
    for all primitive types
    ●
    fallback encoding
    ●
    compatible with
    ●
    virtual dispatch
    ●
    subtyping
    ●
    erased generics
    T (erased to Object)
    T (primitive)
    scalac
    Choice of representation
    1
    2 Coercions between representations
    

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32. scala-ldl.org
    Unboxing Primitive Types
    Value Classes
    Representation Transformations
    Miniboxing
    

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33. scala-ldl.org
    Unboxing Primitive Types
    Value Classes
    Representation Transformations
    Miniboxing
    motivated by
    erased generics
    

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34. scala-ldl.org
    Unboxing Primitive Types
    Value Classes
    Representation Transformations
    Miniboxing
    motivated by
    erased generics
    Staging (Multi-Stage Programming)
    

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35. scala-ldl.org
    Staging
    Staging
    Program
    Result
    1+1+3
    5
    1-stage execution
    

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36. scala-ldl.org
    Staging
    Staging
    Program
    Result
    1+1+3
    5
    1-stage execution
    Program
    Program
    Result
    2+3
    1+1+3
    5
    2-stage execution
    

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37. scala-ldl.org
    Staging
    Staging
    value
    

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38. scala-ldl.org
    Staging
    Staging
    value
    direct value (5)
    ●
    is a computed value
    ●
    from an expression
    evaluated in the
    current stage
    

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39. scala-ldl.org
    Staging
    Staging
    value
    direct value (5)
    ●
    is a computed value
    ●
    from an expression
    evaluated in the
    current stage
    ●
    executed in the next stage
    ●
    stores the expression that
    produces the value
    lifted expression (2+3)
    

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40. scala-ldl.org
    scalac
    Staging
    Staging
    value
    direct value (5)
    ●
    is a computed value
    ●
    from an expression
    evaluated in the
    current stage
    ●
    executed in the next stage
    ●
    stores the expression that
    produces the value
    lifted expression (2+3)
    Choice of representation – domain-specific
    1
    2 Coercions between representations
    

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41. scala-ldl.org
    Motivation
    Transformation
    Conclusion
    Properties
    Benchmarks
    

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42. scala-ldl.org
    How to transform a program?
    

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43. scala-ldl.org
    How to transform a program?
    We'll use primitive unboxing
    as the running example,
    to keep things simple
    

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44. scala-ldl.org
    Syntax-based transformation
    Late Data Layout transformation
    

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45. scala-ldl.org
    Syntax-based transformation
    Late Data Layout transformation
    

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46. scala-ldl.org
    Syntax-based
    Syntax-based
    ●
    we need coercions between representations
    ●
    simple set of syntax-based rules
    – example
    

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47. scala-ldl.org
    Syntax-based
    Syntax-based
    val x: Int = ...
    val y: Int = x
    

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48. scala-ldl.org
    Syntax-based
    Syntax-based
    val x: Int = ...
    val y: Int = x
    

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49. scala-ldl.org
    Syntax-based
    Syntax-based
    val x: Int = ...
    val y: Int = x
    val x: int = unbox(...)
    val y: Int = box(x)
    

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50. scala-ldl.org
    Syntax-based
    Syntax-based
    val x: Int = ...
    val y: Int = x
    val x: int = unbox(...)
    val y: Int = box(x)
    Coerce the definition
    right-hand side
    

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51. scala-ldl.org
    Syntax-based
    Syntax-based
    val x: Int = ...
    val y: Int = x
    val x: int = unbox(...)
    val y: Int = box(x)
    Coerce all occurences of
    the transformed value
    

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52. scala-ldl.org
    Syntax-based
    Syntax-based
    val x: Int = ...
    val y: Int = x
    val x: int = unbox(...)
    val y: Int = box(x)
    

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53. scala-ldl.org
    Syntax-based
    Syntax-based
    val x: Int = ...
    val y: Int = x
    val x: int = unbox(...)
    val y: Int = box(x)
    val x: int = unbox(...)
    val y: int = unbox(box(x))
    

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54. scala-ldl.org
    Syntax-based
    Syntax-based
    val x: Int = ...
    val y: Int = x
    val x: int = unbox(...)
    val y: Int = box(x)
    val x: int = unbox(...)
    val y: int = unbox(box(x))
    suboptimal
    

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55. scala-ldl.org
    Peephole Optimization
    Peephole Optimization
    val y: int = unbox(box(x))
    val y: int = x
    peephole
    

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56. scala-ldl.org
    Syntax-based
    Syntax-based
    another example
    

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57. scala-ldl.org
    Syntax-based
    Syntax-based
    def choice(t1: Int, t2: Int): Int =
    if (Random.nextBoolean())
    t1
    else
    t2
    

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58. scala-ldl.org
    Syntax-based
    Syntax-based
    def choice(t1: Int, t2: Int): Int =
    if (Random.nextBoolean())
    t1
    else
    t2
    Transform one by one
    

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59. scala-ldl.org
    Syntax-based
    Syntax-based
    def choice(t1: int, t2: Int): Int =
    if (Random.nextBoolean())
    box(t1)
    else
    t2
    

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60. scala-ldl.org
    Syntax-based
    Syntax-based
    def choice(t1: int, t2: int): Int =
    if (Random.nextBoolean())
    box(t1)
    else
    box(t2)
    

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61. scala-ldl.org
    Syntax-based
    Syntax-based
    def choice(t1: int, t2: int): Int =
    if (Random.nextBoolean())
    box(t1)
    else
    box(t2)
    Anything missing?
    

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62. scala-ldl.org
    Syntax-based
    Syntax-based
    def choice(t1: int, t2: int): Int =
    if (Random.nextBoolean())
    box(t1)
    else
    box(t2)
    Anything missing?
    Yes, unboxing the returned value
    

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63. scala-ldl.org
    Syntax-based
    Syntax-based
    def choice(t1: int, t2: int): Int =
    if (Random.nextBoolean())
    box(t1)
    else
    box(t2)
    

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64. scala-ldl.org
    Syntax-based
    Syntax-based
    def choice(t1: int, t2: int): Int =
    if (Random.nextBoolean())
    box(t1)
    else
    box(t2)
    

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65. scala-ldl.org
    Syntax-based
    Syntax-based
    def choice(t1: int, t2: int): int =
    if (Random.nextBoolean())
    box(t1)
    else
    box(t2)
    

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66. scala-ldl.org
    Syntax-based
    Syntax-based
    def choice(t1: int, t2: int): int =
    unbox(
    if (Random.nextBoolean())
    box(t1)
    else
    box(t2)
    )
    

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67. scala-ldl.org
    Syntax-based
    Syntax-based
    def choice(t1: int, t2: int): int =
    unbox(
    if (Random.nextBoolean())
    box(t1)
    else
    box(t2)
    )
    

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68. scala-ldl.org
    Syntax-based
    Syntax-based
    def choice(t1: int, t2: int): int =
    unbox(
    if (Random.nextBoolean())
    box(t1)
    else
    box(t2)
    )
    

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69. scala-ldl.org
    Syntax-based
    Syntax-based
    def choice(t1: int, t2: int): int =
    unbox(
    if (Random.nextBoolean())
    box(t1)
    else
    box(t2)
    ) new peephole rule
    

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70. scala-ldl.org
    Syntax-based
    Syntax-based
    def choice(t1: int, t2: int): int =
    unbox(
    if (Random.nextBoolean())
    box(t1)
    else
    box(t2)
    ) new peephole rule
    sink outside coercions
    into the if branches
    

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71. scala-ldl.org
    Syntax-based
    Syntax-based
    def choice(t1: int, t2: int): int =
    if (Random.nextBoolean())
    unbox(box(t1))
    else
    unbox(box(t2))
    

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72. scala-ldl.org
    Syntax-based
    Syntax-based
    def choice(t1: int, t2: int): int =
    if (Random.nextBoolean())
    unbox(box(t1))
    else
    unbox(box(t2))
    

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73. scala-ldl.org
    Syntax-based
    Syntax-based
    def choice(t1: int, t2: int): int =
    if (Random.nextBoolean())
    t1
    else
    t2
    

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74. scala-ldl.org
    Syntax-based
    Syntax-based
    def choice(t1: int, t2: int): int =
    if (Random.nextBoolean())
    t1
    else
    t2
    complicated
    

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75. scala-ldl.org
    Syntax-based
    Syntax-based
    ●
    peephole transformation does not scale
    – needs multiple rewrite rules for each node
    – needs stateful rewrite rules
    – leads to an explosion of rules x states
    Details in
    the paper
    

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76. scala-ldl.org
    Coercions are fixed in the tree
    

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77. scala-ldl.org
    Coercions are fixed in the tree
    and moving them around is difficult.
    

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78. scala-ldl.org
    Coercions are fixed in the tree
    and moving them around is difficult.
    We need a more fluid abstraction.
    

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79. scala-ldl.org
    Coercions are fixed in the tree
    and moving them around is difficult.
    We need a more fluid abstraction.
    Types
    

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80. scala-ldl.org
    Syntax-based transformation
    Late Data Layout transformation
    

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81. scala-ldl.org
    Inject
    Coerce
    Commit
    Phases
    Late Data Layout transformation
    

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82. scala-ldl.org
    LDL Transformation
    LDL Transformation
    ●
    propagates representation information
    – into the type system
    ●
    based on annotated types
    ●
    e.g. an @unboxed annotation added to integers
    The Inject Phase
    The Inject Phase
    

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83. scala-ldl.org
    LDL Transformation
    LDL Transformation
    def choice(t1: Int,
    t2: Int): Int =
    if (Random.nextBoolean())
    t1
    else
    t2
    inject
    coerce
    commit
    

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84. scala-ldl.org
    LDL Transformation
    LDL Transformation
    def choice(t1: @unboxed Int,
    t2: @unboxed Int): @unboxed Int =
    if (Random.nextBoolean())
    t1
    else
    t2
    inject
    coerce
    commit
    

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85. scala-ldl.org
    LDL Transformation
    LDL Transformation
    def choice(t1: @unboxed Int,
    t2: @unboxed Int): @unboxed Int =
    if (Random.nextBoolean())
    t1
    else
    t2
    inject
    coerce
    commit
    depending on the transformation, other
    operations can be performed as well
    (e.g. miniboxing duplicates methods)
    

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86. scala-ldl.org
    Inject
    Coerce
    Commit
    Phases
    Late Data Layout transformation
    

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87. scala-ldl.org
    LDL Transformation
    LDL Transformation
    ●
    introduces coercions
    – re-type-checks the tree
    – exposes representation mismatches
    ●
    as annotation mismatches (Int vs @unboxed Int)
    ●
    leading to coercions
    The Coerce Phase
    The Coerce Phase
    

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88. scala-ldl.org
    LDL Transformation
    LDL Transformation
    def choice(t1: @unboxed Int,
    t2: @unboxed Int): @unboxed Int =
    if (Random.nextBoolean())
    t1
    else
    t2
    inject
    coerce
    commit
    

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89. scala-ldl.org
    LDL Transformation
    LDL Transformation
    def choice(t1: @unboxed Int,
    t2: @unboxed Int): @unboxed Int =
    if (Random.nextBoolean())
    t1
    else
    t2
    inject
    coerce
    commit
    

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90. scala-ldl.org
    LDL Transformation
    LDL Transformation
    def choice(t1: @unboxed Int,
    t2: @unboxed Int): @unboxed Int =
    if (Random.nextBoolean())
    t1
    else
    t2
    inject
    coerce
    commit
    the return type of choice
    is @unboxed Int
    

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91. scala-ldl.org
    LDL Transformation
    LDL Transformation
    def choice(t1: @unboxed Int,
    t2: @unboxed Int): @unboxed Int =
    if (Random.nextBoolean())
    t1
    else
    t2
    inject
    coerce
    commit
    the return type of choice
    is @unboxed Int
    

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92. scala-ldl.org
    LDL Transformation
    LDL Transformation
    def choice(t1: @unboxed Int,
    t2: @unboxed Int): @unboxed Int =
    if (Random.nextBoolean())
    t1
    else
    t2
    inject
    coerce
    commit
    : @unboxed Int
    the return type of choice
    is @unboxed Int
    

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93. scala-ldl.org
    LDL Transformation
    LDL Transformation
    def choice(t1: @unboxed Int,
    t2: @unboxed Int): @unboxed Int =
    if (Random.nextBoolean())
    t1
    else
    t2
    inject
    coerce
    commit
    : @unboxed Int
    expected type
    (part of local type inference)
    the return type of choice
    is @unboxed Int
    

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94. scala-ldl.org
    LDL Transformation
    LDL Transformation
    def choice(t1: @unboxed Int,
    t2: @unboxed Int): @unboxed Int =
    if (Random.nextBoolean())
    t1
    else
    t2
    inject
    coerce
    commit
    : @unboxed Int
    

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95. scala-ldl.org
    LDL Transformation
    LDL Transformation
    def choice(t1: @unboxed Int,
    t2: @unboxed Int): @unboxed Int =
    if (Random.nextBoolean())
    t1
    else
    t2
    inject
    coerce
    commit
    : Boolean
    

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96. scala-ldl.org
    LDL Transformation
    LDL Transformation
    def choice(t1: @unboxed Int,
    t2: @unboxed Int): @unboxed Int =
    if (Random.nextBoolean())
    t1
    else
    t2
    inject
    coerce
    commit
    : Boolean
    matches:
    expected: Boolean
    found: Boolean
    

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97. scala-ldl.org
    LDL Transformation
    LDL Transformation
    def choice(t1: @unboxed Int,
    t2: @unboxed Int): @unboxed Int =
    if (Random.nextBoolean())
    t1
    else
    t2
    inject
    coerce
    commit
    : @unboxed Int
    

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98. scala-ldl.org
    LDL Transformation
    LDL Transformation
    def choice(t1: @unboxed Int,
    t2: @unboxed Int): @unboxed Int =
    if (Random.nextBoolean())
    t1
    else
    t2
    inject
    coerce
    commit
    : @unboxed Int
    matches:
    expected: @unboxed Int
    found: @unboxed Int
    

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99. scala-ldl.org
    LDL Transformation
    LDL Transformation
    def choice(t1: @unboxed Int,
    t2: @unboxed Int): @unboxed Int =
    if (Random.nextBoolean())
    t1
    else
    t2
    inject
    coerce
    commit
    : @unboxed Int
    

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100. scala-ldl.org
     LDL Transformation
     LDL Transformation
     def choice(t1: @unboxed Int,
     t2: @unboxed Int): @unboxed Int =
     if (Random.nextBoolean())
     t1
     else
     t2
     inject
     coerce
     commit
     matches:
     ...
     : @unboxed Int
     

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101. scala-ldl.org
     LDL Transformation
     LDL Transformation
     def choice(t1: @unboxed Int,
     t2: @unboxed Int): @unboxed Int =
     if (Random.nextBoolean())
     t1
     else
     t2
     inject
     coerce
     commit
     

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102. scala-ldl.org
     LDL Transformation
     LDL Transformation
     def choice(t1: @unboxed Int,
     t2: @unboxed Int): @unboxed Int =
     if (Random.nextBoolean())
     t1
     else
     t2
     inject
     coerce
     commit
     LDL optimally transforms
     the tree the first time
     

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103. scala-ldl.org
     LDL Transformation
     LDL Transformation
     def choice(t1: @unboxed Int,
     t2: @unboxed Int): @unboxed Int =
     if (Random.nextBoolean())
     t1
     else
     t2
     inject
     coerce
     commit
     LDL optimally transforms
     the tree the first time
     No peephole transformation
     

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104. scala-ldl.org
     Inject
     Coerce
     Commit
     Phases
     Late Data Layout transformation
     

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105. scala-ldl.org
     LDL Transformation
     LDL Transformation
     ●
     converts annotations to representations
     – @unboxed Int → int
     – Int java.lang.Integer
     →
     ●
     coercion markers are also transformed
     – box(...) → new Integer(...)
     – unbox(...) → ....intValue
     The Commit Phase
     The Commit Phase
     

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106. scala-ldl.org
     LDL Transformation
     LDL Transformation
     def choice(t1: @unboxed Int,
     t2: @unboxed Int): @unboxed Int =
     if (Random.nextBoolean())
     t1
     else
     t2
     inject
     coerce
     commit
     

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107. scala-ldl.org
     LDL Transformation
     LDL Transformation
     def choice(t1: int,
     t2: int): int =
     if (Random.nextBoolean())
     t1
     else
     t2
     inject
     coerce
     commit
     

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108. scala-ldl.org
     LDL Transformation
     LDL Transformation
     def choice(t1: int,
     t2: int): int =
     if (Random.nextBoolean())
     t1
     else
     t2
     inject
     coerce
     commit
     that's it!
     

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109. scala-ldl.org
     Inject
     Coerce
     Commit
     Phases
     Late Data Layout transformation
     

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110. scala-ldl.org
     Motivation
     Transformation
     Conclusion
     Properties
     Benchmarks
     

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111. scala-ldl.org
     Selectivity
     Consistency
     Optimality (not formally proven yet)
     Properties
     Late Data Layout transformation
     

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112. scala-ldl.org
     Selectivity
     Selectivity inject
     coerce
     commit
     ●
     annotated types
     – selectively pick the representation for each value
     

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113. scala-ldl.org
     Selectivity
     Selectivity inject
     coerce
     commit
     ●
     annotated types
     – selectively pick the representation for each value
     ●
     selectivity is used for
     – bridge methods (some args boxed, others unboxed)
     – value classes (JVM: no multi-value returns)
     – staging (representation: domain-specific knowledge)
     ●
     List[Int] vs List[@staged Int] vs @staged List[Int]
     

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114. scala-ldl.org
     Selectivity
     Selectivity
     def choice(t1: Int,
     t2: Int): Int =
     if (Random.nextBoolean())
     t1
     else
     t2
     inject
     coerce
     commit
     

     View Slide

115. scala-ldl.org
     Selectivity
     Selectivity
     def choice(t1: Int,
     t2: Int): Int =
     if (Random.nextBoolean())
     t1
     else
     t2
     inject
     coerce
     commit
     what if we did not annotate t1?
     

     View Slide

116. scala-ldl.org
     Selectivity
     Selectivity
     def choice(t1: Int,
     t2: @unboxed Int): @unboxed Int =
     if (Random.nextBoolean())
     t1
     else
     t2
     inject
     coerce
     commit
     what if we did not annotate t1?
     

     View Slide

117. scala-ldl.org
     Selectivity
     Selectivity
     def choice(t1: Int,
     t2: @unboxed Int): @unboxed Int =
     if (Random.nextBoolean())
     t1
     else
     t2
     inject
     coerce
     commit
     : @unboxed Int
     

     View Slide

118. scala-ldl.org
     Selectivity
     Selectivity
     def choice(t1: Int,
     t2: @unboxed Int): @unboxed Int =
     if (Random.nextBoolean())
     t1
     else
     t2
     inject
     coerce
     commit
     : @unboxed Int
     

     View Slide

119. scala-ldl.org
     Selectivity
     Selectivity
     def choice(t1: Int,
     t2: @unboxed Int): @unboxed Int =
     if (Random.nextBoolean())
     t1
     else
     t2
     inject
     coerce
     commit
     : @unboxed Int
     mismatch:
     expected: @unboxed Int
     found: Int
     

     View Slide

120. scala-ldl.org
     Selectivity
     Selectivity
     def choice(t1: Int,
     t2: @unboxed Int): @unboxed Int =
     if (Random.nextBoolean())
     t1
     else
     t2
     inject
     coerce
     commit
     : @unboxed Int
     mismatch:
     expected: @unboxed Int
     found: Int
     coercion
     

     View Slide

121. scala-ldl.org
     Selectivity
     Selectivity
     def choice(t1: Int,
     t2: @unboxed Int): @unboxed Int =
     if (Random.nextBoolean())
     unbox(t1)
     else
     t2
     inject
     coerce
     commit
     

     View Slide

122. scala-ldl.org
     Selectivity
     Selectivity
     def choice(t1: Int,
     t2: @unboxed Int): @unboxed Int =
     if (Random.nextBoolean())
     unbox(t1)
     else
     t2
     inject
     coerce
     commit
     

     View Slide

123. scala-ldl.org
     Selectivity
     Selectivity
     def choice(t1: java.lang.Integer,
     t2: int): int =
     if (Random.nextBoolean())
     t1.intValue
     else
     t2
     inject
     coerce
     commit
     

     View Slide

124. scala-ldl.org
     Selectivity
     Consistency
     Optimality (not formally proven yet)
     Properties
     Late Data Layout transformation
     

     View Slide

125. scala-ldl.org
     Consistency
     Consistency inject
     coerce
     commit
     ●
     representations become part of types
     ●
     re-type-checking the program
     – proves type correctness
     – proves representation consistency
     

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126. scala-ldl.org
     Selectivity
     Consistency
     Optimality (not formally proven yet)
     Properties
     Late Data Layout transformation
     

     View Slide

127. scala-ldl.org
     Optimality
     Optimality
     def choice(t1: java.lang.Integer,
     t2: int): int =
     if (Random.nextBoolean())
     t1.intValue
     else
     t2
     inject
     coerce
     commit
     

     View Slide

128. scala-ldl.org
     Optimality
     Optimality
     def choice(t1: java.lang.Integer,
     t2: int): int =
     if (Random.nextBoolean())
     t1.intValue
     else
     t2
     execution
     inject
     coerce
     commit
     

     View Slide

129. scala-ldl.org
     Optimality
     Optimality
     def choice(t1: java.lang.Integer,
     t2: int): int =
     if (Random.nextBoolean())
     t1.intValue
     else
     t2
     1 coercion
     execution
     inject
     coerce
     commit
     

     View Slide

130. scala-ldl.org
     Optimality
     Optimality
     def choice(t1: java.lang.Integer,
     t2: int): int =
     if (Random.nextBoolean())
     t1.intValue
     else
     t2
     1 coercion
     no coercions
     execution
     inject
     coerce
     commit
     

     View Slide

131. scala-ldl.org
     Optimality
     Optimality
     ●
     on any execution trace through the program
     – the number of coercions executed is minimum
     – assuming the program terminates
     inject
     coerce
     commit
     

     View Slide

132. scala-ldl.org
     Optimality
     Optimality
     ●
     on any execution trace through the program
     – the number of coercions executed is minimum
     – assuming the program terminates
     ●
     modulo
     – annotations introduced by the inject phase
     ●
     unbox both parameters → no coercions at all
     inject
     coerce
     commit
     

     View Slide

133. scala-ldl.org
     Optimality
     Optimality
     ●
     on any execution trace through the program
     – the number of coercions executed is minimum
     – assuming the program terminates
     ●
     modulo
     – annotations introduced by the inject phase
     ●
     unbox both parameters → no coercions at all
     – post-transformations done by the commit phase
     ●
     box(...) → new Integer(new Integer(...).intValue)
     inject
     coerce
     commit
     

     View Slide

134. scala-ldl.org
     Optimality
     Optimality
     ●
     peephole optimization
     – propagates coercions
     ●
     type system
     – propagates types
     inject
     coerce
     commit
     

     View Slide

135. scala-ldl.org
     Optimality
     Optimality
     ●
     peephole optimization
     – propagates coercions
     ●
     type system
     – propagates types
     – but types are fluid whereas coercions are not
     details in the paper
     inject
     coerce
     commit
     

     View Slide

136. scala-ldl.org
     Selectivity
     Consistency
     Optimality (not formally proven yet)
     Properties
     Late Data Layout transformation
     

     View Slide

137. scala-ldl.org
     Motivation
     Transformation
     Conclusion
     Properties
     Benchmarks
     

     View Slide

138. scala-ldl.org
     LDL is used in
     LDL is used in
     ●
     Scala compiler plugins
     – miniboxing (specialization)
     – value-class plugin
     – staging plugin
     

     View Slide

139. scala-ldl.org
     Benchmarks
     Benchmarks
     …
     … in the paper
     in the paper
     ●
     implementation effort
     – Late Data Layout mechanism
     ●
     developed as part of miniboxing
     ●
     reused by the other compiler plugins
     – value class plugin → 2 developer-weeks
     – staging plugin → 1 developer-week
     

     View Slide

140. scala-ldl.org
     Benchmarks
     Benchmarks
     …
     … in the paper
     in the paper
     ●
     performance
     – baseline vs transformed code
     ●
     numbers
     – up to 2x speedup when transforming value classes
     – up to 22x speedup when using miniboxing
     – up to 59x speedup when staging
     

     View Slide

141. scala-ldl.org
     Motivation
     Transformation
     Conclusion
     Properties
     Benchmarks
     

     View Slide

142. scala-ldl.org
     Conclusion
     Conclusion
     Insights
     Insights
     ●
     use annotated types
     – to selectively mark values with the representation
     ●
     use expected type propagation
     – to provide optimal transformation
     ●
     use the type system
     – to provide representation consistency
     

     View Slide

143. scala-ldl.org
     Credits and Thank you-s
     ●
     Cristian Talau - developed the initial prototype, as a semester project
     ●
     Eugene Burmako - the value class plugin based on the LDL transformation
     ●
     Aymeric Genet - developing collection-like benchmarks for the miniboxing plugin
     ●
     Martin Odersky, for his patient guidance
     ●
     Eugene Burmako, for trusting the idea enough to develop the value-plugin based on the LDL transformation
     ●
     Iulian Dragos, for his work on specialization and many explanations
     ●
     Miguel Garcia, for his original insights that spawned the miniboxing idea
     ●
     Michel Schinz, for his wonderful comments and enlightening ACC course
     ●
     Andrew Myers and Roland Ducournau for the discussions we had and the feedback provided
     ●
     Heather Miller for the eye-opening discussions we had
     ●
     Vojin Jovanovic, Sandro Stucki, Manohar Jonalagedda and the whole LAMP laboratory in EPFL for the extraordinary atmosphere
     ●
     Adriaan Moors, for the miniboxing name which stuck :))
     ●
     Thierry Coppey, Vera Salvisberg and George Nithin, who patiently listened to many presentations and provided valuable feedback
     ●
     Grzegorz Kossakowski, for the many brainstorming sessions on specialization
     ●
     Erik Osheim, Tom Switzer and Rex Kerr for their guidance on the Scala community side
     ●
     OOPSLA paper and artifact reviewers, who reshaped the paper with their feedback
     ●
     Sandro, Vojin, Nada, Heather, Manohar - reviews and discussions on the LDL paper
     ●
     Hubert Plociniczak for the type notation in the LDL paper
     ●
     Denys Shabalin, Dmitry Petrashko for their patient reviews of the LDL paper
     ●
     Xiaoya Xiang and Philip Stutz for trusting miniboxing enough to try it out
     Special thanks to the Scala Community for their support!
     (@StuHood, @vpatryshev and everyone else!)
     

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144. scala-ldl.org
     concept
     repr. 1 … repr. n
     repr. 2
     

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145. scala-ldl.org
     concept
     repr. 1 … repr. n
     repr. 2
     How would
     you use this?
     

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146. scala-ldl.org
     Thank you!
     concept
     repr. 1 … repr. n
     repr. 2
     How would
     you use this?
     

     View Slide