Don't @ Me! Faster Instance Variables with Object Shapes

Transcript

1. Don't @ me!
   Faster Instance Variables with Object Shapes
   

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3. Aaron Patterson
   

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4. 15 min standup
   

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5. Ruby Core Team
   

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6. Rails Core Team
   

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7. @tenderlove
   mastodon.social/@tenderlove
   
   
   GitHub
   
   
   Cohost
   
   
   Instagram
   

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8. LinkedIn: tenderlove
   

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10. Ruby Infrastructure
    

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11. Instance Variables
    

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12. Instance Variables: TMI
    

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13. Object Shapes
    

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14. YJIT
    

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15. All in 30 min! LOL
    

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16. Thanks!!
    🥰🥰🥰🥰🥰🥰🥰🥰🥰
    Ruby Infrastructure
    
    YJIT team
    
    Jemma Issroff
    
    Maxime Chevalier-Boisvert
    
    John Hawthorn @ GitHub
    

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17. How do IVARS work?
    Don't @ me!
    

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18. Instance Variables = IVARs = IVs
    

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19. Implementing
    
    
    Instance Variables
    

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20. Instance Variables
    How to store them?
    class Hello
    
    
    def initialize
    
    
    @foo = 1
    
    
    @bar = 2
    
    
    end
    
    
    def foo
    
    
    @foo + @bar
    
    
    end
    
    
    end
    
    
    Hello.new
    Instance of
    Hello
    IV Hash Table
    IV Name IV Value
    :@foo 1
    :@bar 2
    

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21. Hash based implementation
    If it were written in Ruby
    class Object
    
    
    def initialize
    
    
    @ivs = {} # Magic instance variable hash
    
    
    end
    
    
    def instance_variable_set name, value
    
    
    @ivs[name] = value
    
    
    end
    
    
    def instance_variable_get name
    
    
    @ivs[name]
    
    
    end
    
    
    def instance_variable_defined? name
    
    
    # ooohhh, why did he put this method in the example?
    
    
    # I bet it's foreshadowing!
    
    
    @ivs.key? name
    
    
    end
    
    
    end
    

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22. Ruby <= 1.8.X
    

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23. Tree Walking Interpreter
    class Hello
    
    
    def initialize
    
    
    @foo = 1
    
    
    @bar = 2
    
    
    end
    
    
    def foo
    
    
    @foo + @bar
    
    
    end
    
    
    end
    +
    @foo @bar
    1 2
    3
    Hash Lookup! Hash Lookup!
    

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24. Ruby 1.9: YARV
    

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25. YARV Execution
    Code is compiled to instructions before execution
    class Hello
    
    
    def initialize
    
    
    @foo = 1
    
    
    @bar = 2
    
    
    end
    
    
    def foo
    
    
    @foo + @bar
    
    
    end
    
    
    end
    
    
    hi = Hello.new
    
    
    hi.foo
    Source Code Byte Code for "foo"
    [:getivar, :@foo]
    [:getivar, :@bar]
    [:plus]
    VM Stack
    1
    2
    3
    

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26. Instruction Implementation
    Example implementation written in Ruby
    def getivar name
    
    
    get_self.instance_variables[name]
    
    
    end
    getivar Implementation
    [:getivar, :@foo]
    [:getivar, :@bar]
    [:plus]
    Get self from
    current stack frame
    G
    et H
    ash
    of IVS
    

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27. Hashes are slow
    Compared to Arrays
    

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28. Hashes Use Memory
    Compared to Arrays
    

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29. Lets Use an Array!
    Instead of a Hash!
    

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30. Instance Variables
    How to store them?
    class Hello
    
    
    def initialize
    
    
    @foo = 1
    
    
    @bar = 2
    
    
    end
    
    
    def foo
    
    
    @foo + @bar
    
    
    end
    
    
    end
    
    
    Hello.new
    Instance of
    Hello
    IV Index Table
    Name Index
    :@foo 0
    :@bar 1
    Hello Class
    IV Array
    0 1
    1 2
    

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31. Instance Variables (second instance)
    How to store them?
    class Hello
    
    
    def initialize
    
    
    @foo = 1
    
    
    @bar = 2
    
    
    end
    
    
    def foo
    
    
    @foo + @bar
    
    
    end
    
    
    end
    
    
    Hello.new
    Instance of
    Hello
    IV Index Table
    Name Index
    :@foo 0
    :@bar 1
    Hello Class
    IV Array
    0 1
    1 2
    

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32. Instance Variables (many instances)
    Hash table size is amortized
    class Hello
    
    
    def initialize
    
    
    @foo = 1
    
    
    @bar = 2
    
    
    end
    
    
    def foo
    
    
    @foo + @bar
    
    
    end
    
    
    end
    
    
    Hello.new
    Instance of
    Hello
    IV Index Table
    Name Index
    :@foo 0
    :@bar 1
    Hello Class
    IV Array
    0 1
    1 2
    Instance of
    Hello
    0 1
    1 2
    

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33. Instance Variables Storage Location
    References are stored inside the object (it's in the computer)
    class Hello
    
    
    def initialize
    
    
    @foo = 1
    
    
    @bar = 2
    
    
    end
    
    
    def foo
    
    
    @foo + @bar
    
    
    end
    
    
    end
    
    
    Hello.new
    Instance of
    Hello
    In-Memory Layout
    Byte Index Value
    0 Flags (a 64 bit bitmap)
    8 Pointer to Class
    16
    24
    32
    First IV
    Second IV
    Third IV
    1
    2
    Qundef
    

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34. Storage Location Depends on Type
    Objects store instance variables "in line", others in an external table
    class Hello
    
    
    def initialize
    
    
    @foo = 1
    
    
    @bar = 2
    
    
    end
    
    
    def foo
    
    
    @foo + @bar
    
    
    end
    
    
    end
    class PleaseDoNotDoThis < Array
    
    
    def initialize
    
    
    @foo = 1
    
    
    @bar = 2
    
    
    super
    
    
    end
    
    
    def foo
    
    
    @foo + @bar
    
    
    end
    
    
    end
    

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35. Instruction Implementation
    "foo" method instructions
    def getivar name
    
    
    # get the class
    
    
    klass = get_self.class
    
    
    # get the index of the ivar
    
    
    index = klass.ivar_index[name]
    
    
    if get_self.is_a?(Object)
    
    
    # get the ivar value
    
    
    get_self.instance_variables[index]
    
    
    else
    
    
    # do something different
    
    
    end
    
    
    end
    getivar Implementation
    [:getivar, :@foo]
    [:getivar, :@bar]
    [:plus]
    Still doing a hash
    lookup
    😆
    

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36. Inline Caches
    

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37. Instruction Implementation
    "foo" method instructions, with inline caches
    def getivar name, cache
    
    
    # If there is no cached index
    
    
    unless cache.index
    
    
    # get the class
    
    
    klass = get_self.class
    
    
    # get the index of the ivar
    
    
    index = klass.ivar_index[name]
    
    
    # store the index
    
    
    cache.index = index
    
    
    end
    
    
    # get the cached index
    
    
    index = cache.index
    
    
    if get_self.is_a?(Object)
    
    
    # get the ivar value
    
    
    get_self.instance_variables[index]
    
    
    else
    
    
    # do something different
    
    
    end
    
    
    end
    getivar Implementation
    [:getivar, :@foo, cache]
    [:getivar, :@bar, cache]
    [:plus]
    Find and cache
    the index
    Use the cached
    index
    

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38. Usually No Hash Lookups!
    

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39. Cache Lookup Problem
    Name to Index mapping is per class
    class Hello
    
    
    def initialize
    
    
    @foo = 1
    
    
    @bar = 2
    
    
    end
    
    
    def foo
    
    
    @foo + @bar
    
    
    end
    
    
    end
    
    
    class World < Hello
    
    
    def initialize
    
    
    @oops = "yikes!!"
    
    
    super
    
    
    end
    
    
    end
    
    
    Hello.new.foo
    
    
    World.new.foo
    Instance of
    Hello
    IV Index Table
    Name Index
    :@foo 0
    :@bar 1
    Hello Class
    IV Array
    0 1
    1 2
    Cache Index 0 and 1
    

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40. Cache Lookup Problem
    Name to Index mapping is per class
    class Hello
    
    
    def initialize
    
    
    @foo = 1
    
    
    @bar = 2
    
    
    end
    
    
    def foo
    
    
    @foo + @bar
    
    
    end
    
    
    end
    
    
    class World < Hello
    
    
    def initialize
    
    
    @oops = "yikes!!"
    
    
    super
    
    
    end
    
    
    end
    
    
    Hello.new.foo
    
    
    World.new.foo
    IV Index Table
    Name Index
    :@foo 0
    :@bar 1
    Hello Class
    Cache Index 0 and 1
    Name Index
    :@oops 0
    :@foo 1
    :@bar 2
    World Class
    Oops was
    set
    fi
    rst!
    Oops was
    set
    fi
    rst!
    

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41. Use Class as a Cache Key
    

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42. Compare Class in Cache
    Cache miss if no index or the class doesn't match
    def getivar name, cache
    
    
    # get the class
    
    
    klass = get_self.class
    
    
    # If there is no cached index and class doesn't match
    
    
    if !(cache.index && cache.klass == klass)
    
    
    # get the index of the ivar
    
    
    index = klass.ivar_index[name]
    
    
    # store the index
    
    
    cache.index = index
    
    
    # store the class
    
    
    cache.klass = klass
    
    
    end
    
    
    # get the cached index
    
    
    index = cache.index
    
    
    if get_self.is_a?(Object)
    
    
    # get the ivar value
    
    
    get_self.instance_variables[index]
    
    
    else
    
    
    # do something different
    
    
    end
    
    
    end
    Class must match
    and IV index set
    Return value at
    index inside list
    

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43. Subclasses Cause Cache Misses
    Since the class is a cache key, subclasses can't share cache with superclass
    class Hello
    
    
    def initialize
    
    
    @foo = 1
    
    
    @bar = 2
    
    
    end
    
    
    def foo
    
    
    @foo + @bar
    
    
    end
    
    
    end
    
    
    class World < Hello
    
    
    end
    
    
    hello = Hello.new
    
    
    world = World.new
    
    
    loop do
    
    
    hello.foo
    
    
    world.foo
    
    
    end
    IV Index Table
    Name Index
    :@foo 0
    :@bar 1
    Hello Class
    Name Index
    :@foo 0
    :@bar 1
    World Class
    

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44. 🐵🔧
    

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45. class Hello
    
    
    def initialize(set_bar)
    
    
    @foo = 1
    
    
    @bar = 2 if set_bar
    
    
    @baz = 3
    
    
    end
    
    
    def foo
    
    
    if !instance_variable_defined?(:@bar)
    
    
    puts "oh!"
    
    
    end
    
    
    @foo + @bar.to_i
    
    
    end
    
    
    end
    
    
    p Hello.new(true).foo # => 3
    
    
    p Hello.new(false).foo # => 1
    Handling "Undefined" Instance Variables
    Unde
    fi
    ned IVs return `nil`, but how do we know it's unde
    fi
    ned?
    IV Index Table
    Name Index
    :@foo 0
    :@bar 1
    :@baz 2
    Hello Class
    Hello Instance
    In-Memory Layout
    Byte Value
    0 Flags (a 64 bit bitmap)
    8 Pointer to Class
    16 1
    24 2
    32 3
    

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46. class Hello
    
    
    def initialize(set_bar)
    
    
    @foo = 1
    
    
    @bar = 2 if set_bar
    
    
    @baz = 3
    
    
    end
    
    
    def foo
    
    
    if !instance_variable_defined?(:@bar)
    
    
    puts "oh!"
    
    
    end
    
    
    @foo + @bar.to_i
    
    
    end
    
    
    end
    
    
    p Hello.new(true).foo # => 3
    
    
    p Hello.new(false).foo # => 1
    Handling "Undefined" Instance Variables
    Unde
    fi
    ned IVs return `nil`, but how do we know it's unde
    fi
    ned?
    IV Index Table
    Name Index
    :@foo 0
    :@bar 1
    :@baz 2
    Hello Class
    Hello Instance
    In-Memory Layout
    Byte Value
    0 Flags (a 64 bit bitmap)
    8 Pointer to Class
    16 1
    24 Qundef (0x24)
    32 3
    Cache Index 0 and 1
    

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47. Return `nil` for Undefined IVs
    If the value stored in the array is Qundef, return nil, otherwise return the value
    def getivar name, cache
    
    
    # get the class
    
    
    klass = get_self.class
    
    
    # If there is no cached index and class doesn't match
    
    
    if !(cache.index && cache.klass == klass)
    
    
    # get the index of the ivar
    
    
    index = klass.ivar_index[name]
    
    
    # store the index
    
    
    cache.index = index
    
    
    # store the class
    
    
    cache.klass = klass
    
    
    end
    
    
    # get the cached index
    
    
    index = cache.index
    
    
    if get_self.is_a?(Object)
    
    
    # get the ivar value
    
    
    iv = get_self.instance_variables[index]
    
    
    if iv == Qundef
    
    
    nil
    
    
    else
    
    
    iv
    
    
    end
    
    
    else
    
    
    # do something different
    
    
    end
    
    
    end
    Return nil if Qundef
    

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48. 😫😫😫😫😫
    

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49. Conditionals for Reading an IV
    Just a Recap!
    • Is an index set?
    
    
    • Do the classes match?
    
    
    • Is it an "Object" type?
    
    
    • Is the IV value equal to Qundef?
    

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50. JIT Compilation
    

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51. JIT Compilation
    JIT compiler translates byte code to machine code
    class Hello
    
    
    def initialize
    
    
    @foo = 1
    
    
    @bar = 2
    
    
    end
    
    
    def foo
    
    
    @foo + @bar
    
    
    end
    
    
    end
    
    
    hi = Hello.new
    
    
    hi.foo
    Source Code Byte Code for "foo"
    [:getivar, :@foo, cache]
    [:getivar, :@bar, cache]
    [:plus]
    Machine Code
    == BLOCK 1/5, ISEQ RANGE [0,3), 93 bytes ======================
    
    
    # getinstancevariable
    
    
    # guard not immediate
    
    
    0x55a658d0a6dd: test qword ptr [r13 + 0x18], 7
    
    
    0x55a658d0a6e5: jne 0x55a660d0a0e5
    
    
    0x55a658d0a6eb: cmp qword ptr [r13 + 0x18], 8
    
    
    0x55a658d0a6f0: jbe 0x55a660d0a0fe
    
    
    0x55a658d0a6f6: mov rax, qword ptr [r13 + 0x18]
    
    
    # guard known class
    
    
    0x55a658d0a6fa: movabs rcx, 0x7fbb2af48f20
    
    
    0x55a658d0a704: cmp qword ptr [rax + 8], rcx
    
    
    0x55a658d0a708: jne 0x55a660d0a117
    
    
    0x55a658d0a70e: mov rax, qword ptr [r13 + 0x18]
    
    
    0x55a658d0a712: cmp qword ptr [rax + 0x10], 0
    
    
    0x55a658d0a717: jbe 0x55a660d0a0cc
    
    
    # guard embedded getivar
    
    
    0x55a658d0a71d: test word ptr [rax], 0x2000
    
    
    0x55a658d0a722: je 0x55a660d0a130
    
    
    0x55a658d0a728: cmp qword ptr [rax + 0x18], 0x34
    
    
    0x55a658d0a72d: mov ecx, 8
    
    
    0x55a658d0a732: cmovne rcx, qword ptr [rax + 0x18]
    
    
    0x55a658d0a737: mov qword ptr [rbx], rcx
    
    
    == BLOCK 2/5, ISEQ RANGE [3,6), 0 bytes =======================
    
    
    == BLOCK 3/5, ISEQ RANGE [3,6), 69 bytes ======================
    
    
    # getinstancevariable
    
    
    # regenerate_branch
    
    
    # getinstancevariable
    
    
    # regenerate_branch
    
    
    0x55a658d0a73a: mov rax, qword ptr [r13 + 0x18]
    
    
    # guard known class
    
    
    0x55a658d0a73e: movabs rcx, 0x7fbb2af48f20
    
    
    0x55a658d0a748: cmp qword ptr [rax + 8], rcx
    
    
    0x55a658d0a74c: jne 0x55a660d0a183
    
    
    0x55a658d0a752: mov rax, qword ptr [r13 + 0x18]
    
    
    0x55a658d0a756: cmp qword ptr [rax + 0x10], 1
    
    
    0x55a658d0a75b: jbe 0x55a660d0a162
    
    
    # guard embedded getivar
    
    
    0x55a658d0a761: test word ptr [rax], 0x2000
    
    
    0x55a658d0a766: je 0x55a660d0a19c
    
    
    0x55a658d0a76c: cmp qword ptr [rax + 0x20], 0x34
    
    
    0x55a658d0a771: mov ecx, 8
    
    
    0x55a658d0a776: cmovne rcx, qword ptr [rax + 0x20]
    
    
    0x55a658d0a77b: mov qword ptr [rbx + 8], rcx
    
    
    == BLOCK 4/5, ISEQ RANGE [6,8), 0 bytes =======================
    
    
    == BLOCK 5/5, ISEQ RANGE [6,9), 86 bytes ======================
    
    
    # opt_plus
    
    
    # regenerate_branch
    
    
    # opt_plus
    
    
    # guard arg0 fixnum
    
    
    # regenerate_branch
    
    
    0x55a658d0a77f: test byte ptr [rbx], 1
    
    
    0x55a658d0a782: je 0x55a660d0a1ef
    
    
    # guard arg1 fixnum
    
    
    0x55a658d0a788: test byte ptr [rbx + 8], 1
    
    
    0x55a658d0a78c: je 0x55a660d0a208
    
    
    0x55a658d0a792: mov rax, qword ptr [rbx]
    
    
    0x55a658d0a795: sub rax, 1
    
    
    0x55a658d0a799: add rax, qword ptr [rbx + 8]
    
    
    0x55a658d0a79d: jo 0x55a660d0a1ce
    
    
    0x55a658d0a7a3: mov qword ptr [rbx], rax
    
    
    # leave
    
    
    # RUBY_VM_CHECK_INTS(ec)
    
    
    0x55a658d0a7a6: mov eax, dword ptr [r12 + 0x24]
    
    
    0x55a658d0a7ab: not eax
    
    
    0x55a658d0a7ad: test dword ptr [r12 + 0x20], eax
    
    
    0x55a658d0a7b2: jne 0x55a660d0a221
    
    
    # pop stack frame
    
    
    0x55a658d0a7b8: mov rax, r13
    
    
    0x55a658d0a7bb: add rax, 0x40
    
    
    0x55a658d0a7bf: mov r13, rax
    
    
    Machine Code
    == BLOCK 1/5, ISEQ RANGE [0,3), 93 bytes ======================
    
    
    # getinstancevariable
    
    
    # guard not immediate
    
    
    0x55a658d0a6dd: test qword ptr [r13 + 0x18], 7
    
    
    0x55a658d0a6e5: jne 0x55a660d0a0e5
    
    
    0x55a658d0a6eb: cmp qword ptr [r13 + 0x18], 8
    
    
    0x55a658d0a6f0: jbe 0x55a660d0a0fe
    
    
    0x55a658d0a6f6: mov rax, qword ptr [r13 + 0x18]
    
    
    # guard known class
    
    
    0x55a658d0a6fa: movabs rcx, 0x7fbb2af48f20
    
    
    0x55a658d0a704: cmp qword ptr [rax + 8], rcx
    
    
    0x55a658d0a708: jne 0x55a660d0a117
    
    
    0x55a658d0a70e: mov rax, qword ptr [r13 + 0x18]
    
    
    0x55a658d0a712: cmp qword ptr [rax + 0x10], 0
    
    
    0x55a658d0a717: jbe 0x55a660d0a0cc
    
    
    # guard embedded getivar
    
    
    0x55a658d0a71d: test word ptr [rax], 0x2000
    
    
    0x55a658d0a722: je 0x55a660d0a130
    
    
    0x55a658d0a728: cmp qword ptr [rax + 0x18], 0x34
    
    
    0x55a658d0a72d: mov ecx, 8
    
    
    0x55a658d0a732: cmovne rcx, qword ptr [rax + 0x18]
    
    
    0x55a658d0a737: mov qword ptr [rbx], rcx
    
    
    == BLOCK 2/5, ISEQ RANGE [3,6), 0 bytes =======================
    
    
    == BLOCK 3/5, ISEQ RANGE [3,6), 69 bytes ======================
    
    
    # getinstancevariable
    
    
    # regenerate_branch
    
    
    # getinstancevariable
    
    
    # regenerate_branch
    
    
    0x55a658d0a73a: mov rax, qword ptr [r13 + 0x18]
    
    
    # guard known class
    
    
    0x55a658d0a73e: movabs rcx, 0x7fbb2af48f20
    
    
    0x55a658d0a748: cmp qword ptr [rax + 8], rcx
    
    
    0x55a658d0a74c: jne 0x55a660d0a183
    
    
    0x55a658d0a752: mov rax, qword ptr [r13 + 0x18]
    
    
    0x55a658d0a756: cmp qword ptr [rax + 0x10], 1
    
    
    0x55a658d0a75b: jbe 0x55a660d0a162
    
    
    # guard embedded getivar
    
    
    0x55a658d0a761: test word ptr [rax], 0x2000
    
    
    0x55a658d0a766: je 0x55a660d0a19c
    
    
    0x55a658d0a76c: cmp qword ptr [rax + 0x20], 0x34
    
    
    0x55a658d0a771: mov ecx, 8
    
    
    0x55a658d0a776: cmovne rcx, qword ptr [rax + 0x20]
    
    
    0x55a658d0a77b: mov qword ptr [rbx + 8], rcx
    
    
    == BLOCK 4/5, ISEQ RANGE [6,8), 0 bytes =======================
    
    
    == BLOCK 5/5, ISEQ RANGE [6,9), 86 bytes ======================
    
    
    # opt_plus
    
    
    # regenerate_branch
    
    
    # opt_plus
    
    
    # guard arg0 fixnum
    
    
    # regenerate_branch
    
    
    0x55a658d0a77f: test byte ptr [rbx], 1
    
    
    0x55a658d0a782: je 0x55a660d0a1ef
    
    
    # guard arg1 fixnum
    
    
    0x55a658d0a788: test byte ptr [rbx + 8], 1
    
    
    0x55a658d0a78c: je 0x55a660d0a208
    
    
    0x55a658d0a792: mov rax, qword ptr [rbx]
    
    
    0x55a658d0a795: sub rax, 1
    
    
    0x55a658d0a799: add rax, qword ptr [rbx + 8]
    
    
    0x55a658d0a79d: jo 0x55a660d0a1ce
    
    
    0x55a658d0a7a3: mov qword ptr [rbx], rax
    
    
    # leave
    
    
    # RUBY_VM_CHECK_INTS(ec)
    
    
    0x55a658d0a7a6: mov eax, dword ptr [r12 + 0x24]
    
    
    0x55a658d0a7ab: not eax
    
    
    0x55a658d0a7ad: test dword ptr [r12 + 0x20], eax
    
    
    0x55a658d0a7b2: jne 0x55a660d0a221
    
    
    # pop stack frame
    
    
    0x55a658d0a7b8: mov rax, r13
    
    
    0x55a658d0a7bb: add rax, 0x40
    
    
    0x55a658d0a7bf: mov r13, rax
    
    
    Machine Code
    == BLOCK 1/5, ISEQ RANGE [0,3), 93 bytes ======================
    
    
    # getinstancevariable
    
    
    # guard not immediate
    
    
    0x55a658d0a6dd: test qword ptr [r13 + 0x18], 7
    
    
    0x55a658d0a6e5: jne 0x55a660d0a0e5
    
    
    0x55a658d0a6eb: cmp qword ptr [r13 + 0x18], 8
    
    
    0x55a658d0a6f0: jbe 0x55a660d0a0fe
    
    
    0x55a658d0a6f6: mov rax, qword ptr [r13 + 0x18]
    
    
    # guard known class
    
    
    0x55a658d0a6fa: movabs rcx, 0x7fbb2af48f20
    
    
    0x55a658d0a704: cmp qword ptr [rax + 8], rcx
    
    
    0x55a658d0a708: jne 0x55a660d0a117
    
    
    0x55a658d0a70e: mov rax, qword ptr [r13 + 0x18]
    
    
    0x55a658d0a712: cmp qword ptr [rax + 0x10], 0
    
    
    0x55a658d0a717: jbe 0x55a660d0a0cc
    
    
    # guard embedded getivar
    
    
    0x55a658d0a71d: test word ptr [rax], 0x2000
    
    
    0x55a658d0a722: je 0x55a660d0a130
    
    
    0x55a658d0a728: cmp qword ptr [rax + 0x18], 0x34
    
    
    0x55a658d0a72d: mov ecx, 8
    
    
    0x55a658d0a732: cmovne rcx, qword ptr [rax + 0x18]
    
    
    0x55a658d0a737: mov qword ptr [rbx], rcx
    
    
    == BLOCK 2/5, ISEQ RANGE [3,6), 0 bytes =======================
    
    
    == BLOCK 3/5, ISEQ RANGE [3,6), 69 bytes ======================
    
    
    # getinstancevariable
    
    
    # regenerate_branch
    
    
    # getinstancevariable
    
    
    # regenerate_branch
    
    
    0x55a658d0a73a: mov rax, qword ptr [r13 + 0x18]
    
    
    # guard known class
    
    
    0x55a658d0a73e: movabs rcx, 0x7fbb2af48f20
    
    
    0x55a658d0a748: cmp qword ptr [rax + 8], rcx
    
    
    0x55a658d0a74c: jne 0x55a660d0a183
    
    
    0x55a658d0a752: mov rax, qword ptr [r13 + 0x18]
    
    
    0x55a658d0a756: cmp qword ptr [rax + 0x10], 1
    
    
    0x55a658d0a75b: jbe 0x55a660d0a162
    
    
    # guard embedded getivar
    
    
    0x55a658d0a761: test word ptr [rax], 0x2000
    
    
    0x55a658d0a766: je 0x55a660d0a19c
    
    
    0x55a658d0a76c: cmp qword ptr [rax + 0x20], 0x34
    
    
    0x55a658d0a771: mov ecx, 8
    
    
    0x55a658d0a776: cmovne rcx, qword ptr [rax + 0x20]
    
    
    0x55a658d0a77b: mov qword ptr [rbx + 8], rcx
    
    
    == BLOCK 4/5, ISEQ RANGE [6,8), 0 bytes =======================
    
    
    == BLOCK 5/5, ISEQ RANGE [6,9), 86 bytes ======================
    
    
    # opt_plus
    
    
    # regenerate_branch
    
    
    # opt_plus
    
    
    # guard arg0 fixnum
    
    
    # regenerate_branch
    
    
    0x55a658d0a77f: test byte ptr [rbx], 1
    
    
    0x55a658d0a782: je 0x55a660d0a1ef
    
    
    # guard arg1 fixnum
    
    
    0x55a658d0a788: test byte ptr [rbx + 8], 1
    
    
    0x55a658d0a78c: je 0x55a660d0a208
    
    
    0x55a658d0a792: mov rax, qword ptr [rbx]
    
    
    0x55a658d0a795: sub rax, 1
    
    
    0x55a658d0a799: add rax, qword ptr [rbx + 8]
    
    
    0x55a658d0a79d: jo 0x55a660d0a1ce
    
    
    0x55a658d0a7a3: mov qword ptr [rbx], rax
    
    
    # leave
    
    
    # RUBY_VM_CHECK_INTS(ec)
    
    
    0x55a658d0a7a6: mov eax, dword ptr [r12 + 0x24]
    
    
    0x55a658d0a7ab: not eax
    
    
    0x55a658d0a7ad: test dword ptr [r12 + 0x20], eax
    
    
    0x55a658d0a7b2: jne 0x55a660d0a221
    
    
    # pop stack frame
    
    
    0x55a658d0a7b8: mov rax, r13
    
    
    0x55a658d0a7bb: add rax, 0x40
    
    
    0x55a658d0a7bf: mov r13, rax
    
    
    Machine Code
    

    View Slide

52. Machine Code for Reading an IV
    def getivar name, cache
    
    
    # get the class
    
    
    klass = get_self.class
    
    
    # If there is no cached index and class doesn't match
    
    
    if !(cache.index && cache.klass == klass)
    
    
    # get the index of the ivar
    
    
    index = klass.ivar_index[name]
    
    
    # store the index
    
    
    cache.index = index
    
    
    # store the class
    
    
    cache.klass = klass
    
    
    end
    
    
    # get the cached index
    
    
    index = cache.index
    
    
    if get_self.is_a?(Object)
    
    
    # get the ivar value
    
    
    iv = get_self.instance_variables[index]
    
    
    if iv == Qundef
    
    
    nil
    
    
    else
    
    
    iv
    
    
    end
    
    
    else
    
    
    # do something different
    
    
    end
    
    
    end
    Instruction Implementation
    == BLOCK 1/5, ISEQ RANGE [0,3), 93 bytes ======================
    
    
    # getinstancevariable
    
    
    # guard not immediate
    
    
    0x55a658d0a6dd: test qword ptr [r13 + 0x18], 7
    
    
    0x55a658d0a6e5: jne 0x55a660d0a0e5
    
    
    0x55a658d0a6eb: cmp qword ptr [r13 + 0x18], 8
    
    
    0x55a658d0a6f0: jbe 0x55a660d0a0fe
    
    
    0x55a658d0a6f6: mov rax, qword ptr [r13 + 0x18]
    
    
    # guard known class
    
    
    0x55a658d0a6fa: movabs rcx, 0x7fbb2af48f20
    
    
    0x55a658d0a704: cmp qword ptr [rax + 8], rcx
    
    
    0x55a658d0a708: jne 0x55a660d0a117
    
    
    0x55a658d0a70e: mov rax, qword ptr [r13 + 0x18]
    
    
    0x55a658d0a712: cmp qword ptr [rax + 0x10], 0
    
    
    0x55a658d0a717: jbe 0x55a660d0a0cc
    
    
    # guard embedded getivar
    
    
    0x55a658d0a71d: test word ptr [rax], 0x2000
    
    
    0x55a658d0a722: je 0x55a660d0a130
    
    
    0x55a658d0a728: cmp qword ptr [rax + 0x18], 0x34
    
    
    0x55a658d0a72d: mov ecx, 8
    
    
    0x55a658d0a732: cmovne rcx, qword ptr [rax + 0x18]
    
    
    0x55a658d0a737: mov qword ptr [rbx], rcx
    Generated Machine Code
    def getivar name, cache
    
    
    # get the class
    
    
    klass = get_self.class
    
    
    # If there is no cached index and class doesn't match
    
    
    if !(cache.index && cache.klass == klass)
    
    
    # get the index of the ivar
    
    
    index = klass.ivar_index[name]
    
    
    # store the index
    
    
    cache.index = index
    
    
    # store the class
    
    
    cache.klass = klass
    
    
    end
    
    
    # get the cached index
    
    
    index = cache.index
    
    
    if get_self.is_a?(Object)
    
    
    # get the ivar value
    
    
    iv = get_self.instance_variables[index]
    
    
    if iv == Qundef
    
    
    nil
    
    
    else
    
    
    iv
    
    
    end
    
    
    else
    
    
    # do something different
    
    
    end
    
    
    end
    Instruction Implementation
    == BLOCK 1/5, ISEQ RANGE [0,3), 93 bytes ======================
    
    
    # getinstancevariable
    
    
    # guard not immediate
    
    
    0x55a658d0a6dd: test qword ptr [r13 + 0x18], 7
    
    
    0x55a658d0a6e5: jne 0x55a660d0a0e5
    
    
    0x55a658d0a6eb: cmp qword ptr [r13 + 0x18], 8
    
    
    0x55a658d0a6f0: jbe 0x55a660d0a0fe
    
    
    0x55a658d0a6f6: mov rax, qword ptr [r13 + 0x18]
    
    
    # guard known class
    
    
    0x55a658d0a6fa: movabs rcx, 0x7fbb2af48f20
    
    
    0x55a658d0a704: cmp qword ptr [rax + 8], rcx
    
    
    0x55a658d0a708: jne 0x55a660d0a117
    
    
    0x55a658d0a70e: mov rax, qword ptr [r13 + 0x18]
    
    
    0x55a658d0a712: cmp qword ptr [rax + 0x10], 0
    
    
    0x55a658d0a717: jbe 0x55a660d0a0cc
    
    
    # guard embedded getivar
    
    
    0x55a658d0a71d: test word ptr [rax], 0x2000
    
    
    0x55a658d0a722: je 0x55a660d0a130
    
    
    0x55a658d0a728: cmp qword ptr [rax + 0x18], 0x34
    
    
    0x55a658d0a72d: mov ecx, 8
    
    
    0x55a658d0a732: cmovne rcx, qword ptr [rax + 0x18]
    
    
    0x55a658d0a737: mov qword ptr [rbx], rcx
    Generated Machine Code
    def getivar name, cache
    
    
    # get the class
    
    
    klass = get_self.class
    
    
    # If there is no cached index and class doesn't match
    
    
    if !(cache.index && cache.klass == klass)
    
    
    # get the index of the ivar
    
    
    index = klass.ivar_index[name]
    
    
    # store the index
    
    
    cache.index = index
    
    
    # store the class
    
    
    cache.klass = klass
    
    
    end
    
    
    # get the cached index
    
    
    index = cache.index
    
    
    if get_self.is_a?(Object)
    
    
    # get the ivar value
    
    
    iv = get_self.instance_variables[index]
    
    
    if iv == Qundef
    
    
    nil
    
    
    else
    
    
    iv
    
    
    end
    
    
    else
    
    
    # do something different
    
    
    end
    
    
    end
    Instruction Implementation
    == BLOCK 1/5, ISEQ RANGE [0,3), 93 bytes ======================
    
    
    # getinstancevariable
    
    
    # guard not immediate
    
    
    0x55a658d0a6dd: test qword ptr [r13 + 0x18], 7
    
    
    0x55a658d0a6e5: jne 0x55a660d0a0e5
    
    
    0x55a658d0a6eb: cmp qword ptr [r13 + 0x18], 8
    
    
    0x55a658d0a6f0: jbe 0x55a660d0a0fe
    
    
    0x55a658d0a6f6: mov rax, qword ptr [r13 + 0x18]
    
    
    # guard known class
    
    
    0x55a658d0a6fa: movabs rcx, 0x7fbb2af48f20
    
    
    0x55a658d0a704: cmp qword ptr [rax + 8], rcx
    
    
    0x55a658d0a708: jne 0x55a660d0a117
    
    
    0x55a658d0a70e: mov rax, qword ptr [r13 + 0x18]
    
    
    0x55a658d0a712: cmp qword ptr [rax + 0x10], 0
    
    
    0x55a658d0a717: jbe 0x55a660d0a0cc
    
    
    # guard embedded getivar
    
    
    0x55a658d0a71d: test word ptr [rax], 0x2000
    
    
    0x55a658d0a722: je 0x55a660d0a130
    
    
    0x55a658d0a728: cmp qword ptr [rax + 0x18], 0x34
    
    
    0x55a658d0a72d: mov ecx, 8
    
    
    0x55a658d0a732: cmovne rcx, qword ptr [rax + 0x18]
    
    
    0x55a658d0a737: mov qword ptr [rbx], rcx
    Generated Machine Code
    def getivar name, cache
    
    
    # get the class
    
    
    klass = get_self.class
    
    
    # If there is no cached index and class doesn't match
    
    
    if !(cache.index && cache.klass == klass)
    
    
    # get the index of the ivar
    
    
    index = klass.ivar_index[name]
    
    
    # store the index
    
    
    cache.index = index
    
    
    # store the class
    
    
    cache.klass = klass
    
    
    end
    
    
    # get the cached index
    
    
    index = cache.index
    
    
    if get_self.is_a?(Object)
    
    
    # get the ivar value
    
    
    iv = get_self.instance_variables[index]
    
    
    if iv == Qundef
    
    
    nil
    
    
    else
    
    
    iv
    
    
    end
    
    
    else
    
    
    # do something different
    
    
    end
    
    
    end
    Instruction Implementation
    == BLOCK 1/5, ISEQ RANGE [0,3), 93 bytes ======================
    
    
    # getinstancevariable
    
    
    # guard not immediate
    
    
    0x55a658d0a6dd: test qword ptr [r13 + 0x18], 7
    
    
    0x55a658d0a6e5: jne 0x55a660d0a0e5
    
    
    0x55a658d0a6eb: cmp qword ptr [r13 + 0x18], 8
    
    
    0x55a658d0a6f0: jbe 0x55a660d0a0fe
    
    
    0x55a658d0a6f6: mov rax, qword ptr [r13 + 0x18]
    
    
    # guard known class
    
    
    0x55a658d0a6fa: movabs rcx, 0x7fbb2af48f20
    
    
    0x55a658d0a704: cmp qword ptr [rax + 8], rcx
    
    
    0x55a658d0a708: jne 0x55a660d0a117
    
    
    0x55a658d0a70e: mov rax, qword ptr [r13 + 0x18]
    
    
    0x55a658d0a712: cmp qword ptr [rax + 0x10], 0
    
    
    0x55a658d0a717: jbe 0x55a660d0a0cc
    
    
    # guard embedded getivar
    
    
    0x55a658d0a71d: test word ptr [rax], 0x2000
    
    
    0x55a658d0a722: je 0x55a660d0a130
    
    
    0x55a658d0a728: cmp qword ptr [rax + 0x18], 0x34
    
    
    0x55a658d0a72d: mov ecx, 8
    
    
    0x55a658d0a732: cmovne rcx, qword ptr [rax + 0x18]
    
    
    0x55a658d0a737: mov qword ptr [rbx], rcx
    Generated Machine Code
    def getivar name, cache
    
    
    # get the class
    
    
    klass = get_self.class
    
    
    # If there is no cached index and class doesn't match
    
    
    if !(cache.index && cache.klass == klass)
    
    
    # get the index of the ivar
    
    
    index = klass.ivar_index[name]
    
    
    # store the index
    
    
    cache.index = index
    
    
    # store the class
    
    
    cache.klass = klass
    
    
    end
    
    
    # get the cached index
    
    
    index = cache.index
    
    
    if get_self.is_a?(Object)
    
    
    # get the ivar value
    
    
    iv = get_self.instance_variables[index]
    
    
    if iv == Qundef
    
    
    nil
    
    
    else
    
    
    iv
    
    
    end
    
    
    else
    
    
    # do something different
    
    
    end
    
    
    end
    Instruction Implementation
    

    View Slide

53. 93 Bytes for 1 IV
    

    View Slide

54. We Can Do Better!
    

    View Slide

55. Object Shapes
    

    View Slide

56. Not these shapes
    

    View Slide

57. View Slide

58. Shape Transitions on Write
    Shapes form a tree representing Object properties
    class Hello
    
    
    def initialize
    
    
    @foo = 1
    
    
    @bar = 2
    
    
    end
    
    
    def foo
    
    
    @foo + @bar
    
    
    end
    
    
    end
    Sample Code Shape Tree
    Root
    
    
    id: 0
    @foo
    
    
    id: 1, index: 0
    @bar
    
    
    id: 2, index: 1
    @foo
    @bar
    from: 0, to: 1, iv index: 0
    from:1, to: 2, iv index: 1
    Cache Key
    Cache Key
    Destination
    Shape
    Destination
    Shape
    IV Index
    IV Index
    

    View Slide

59. Shape Tree
    Shape Transitions on Write
    Shape ID is used as the cache key
    class Hello
    
    
    def initialize
    
    
    @foo = 1
    
    
    @bar = 2
    
    
    end
    
    
    def foo
    
    
    @foo + @bar
    
    
    end
    
    
    end
    Sample Code
    Root
    
    
    id: 0
    @foo
    
    
    id: 1, index: 0
    @bar
    
    
    id: 2, index: 1
    @foo
    @bar
    from: 0, to: 1, iv index: 0
    from:1, to: 2, iv index: 1
    

    View Slide

60. Shapes Form a Graph
    

    View Slide

61. All Object Start From a
    
    
    "Root Shape"
    

    View Slide

62. Objects Only Change Shape
    
    
    on Writes
    

    View Slide

63. Shape ID is the Cache Key
    

    View Slide

64. Class is not a cache key
    

    View Slide

65. Object can share shapes
    Hello and World can share caches
    class Hello
    
    
    def initialize
    
    
    @foo = 1
    
    
    @bar = 2
    
    
    end
    
    
    end
    
    
    class World < Hello
    
    
    def initialize
    
    
    super
    
    
    @baz = 3
    
    
    end
    
    
    end
    
    
    Sample Code Shape Tree
    from: 0, to: 1, iv index: 0
    from:1, to: 2, iv index: 1
    from:2, to: 3, iv index: 2
    Root
    
    
    id: 0
    @foo
    
    
    id: 1, index: 0
    @bar
    
    
    id: 2, index: 1
    @baz
    
    
    id:3, index:2
    Shared between
    Hello and World
    instances
    

    View Slide

66. Cross Type Memory Amortization
    

    View Slide

67. Cross Type Cache Hits
    

    View Slide

68. Shared Shape Tree
    Shape Tree is Shared
    All objects use the shape tree, so more types can share info
    class Hello
    
    
    def initialize
    
    
    @foo = 1
    
    
    @bar = 2
    
    
    end
    
    
    def foo
    
    
    @foo + @bar
    
    
    end
    
    
    end
    
    
    class World < Hello
    
    
    end
    
    
    hello = Hello.new
    
    
    world = World.new
    
    
    loop do
    
    
    hello.foo
    
    
    world.foo
    
    
    end
    IV Index Table
    Name Index
    :@foo 0
    :@bar 1
    Hello Class
    Name Index
    :@foo 0
    :@bar 1
    World Class
    Root
    
    
    id: 0
    @foo
    
    
    id: 1, index: 0
    @bar
    
    
    id: 2, index: 1
    Same shape on
    both instances
    Cache Shape 2 and 2
    

    View Slide

69. Cross Type Cache Hits
    require 'harness'
    
    
    class Hello
    
    
    def initialize
    
    
    @foo = 1
    
    
    @bar = 2
    
    
    end
    
    
    def foo
    
    
    @foo + @bar
    
    
    end
    
    
    end
    
    
    class World < Hello
    
    
    end
    
    
    hello = Hello.new
    
    
    world = World.new
    
    
    run_benchmark(100) do
    
    
    i = 0
    
    
    while i < 90_000
    
    
    hello.foo
    
    
    world.foo
    
    
    i += 1
    
    
    end
    
    
    end
    Microbenchmark
    before: ruby 3.2.0dev (2022-09-28T14:51:38Z before-shapes a05b261464) [x86_64-linux]
    
    
    after: ruby 3.2.0dev (2022-11-22T05:20:45Z master 20b9d7b9fd) [x86_64-linux]
    
    
    ------------------- ----------- ---------- ---------- ---------- ------------ -------------
    
    
    bench before (ms) stddev (%) after (ms) stddev (%) before/after after 1st itr
    
    
    getivar-polymorphic 12.1 1.4 4.4 2.1 2.76 2.82
    
    
    ------------------- ----------- ---------- ---------- ---------- ------------ -------------
    
    
    Legend:
    
    
    - before/after: ratio of before/after time. Higher is better for after. Above 1 represents a speedup.
    
    
    - after 1st itr: ratio of before/after time for the first benchmarking iteration.
    
    
    Results
    2.76x Faster
    

    View Slide

70. Memory Usage Improvements
    

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71. Classes store their name as an IV
    

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72. Class Name is an IV
    Class names are stored as an instance variable on the class instance
    class Hello
    
    
    def initialize
    
    
    @foo = 1
    
    
    @bar = 2
    
    
    end
    
    
    def foo
    
    
    @foo + @bar
    
    
    end
    
    
    end
    
    
    puts Hello.name # => IV read
    

    View Slide

73. View Slide

74. View Slide

75. Not All Properties Are
    
    
    Instance Variables
    

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76. Freezing is a shape transition
    

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77. Freezing Changes Shape
    When we freeze an object, it changes shape
    class Hello
    
    
    def initialize
    
    
    @foo = 1
    
    
    @bar = 2
    
    
    end
    
    
    def set
    
    
    @baz = 3
    
    
    end
    
    
    end
    
    
    hello = Hello.new
    
    
    hello.set
    
    
    hello = Hello.new
    
    
    hello.freeze
    
    
    hello.set
    Sample Code Shape Tree
    Root
    
    
    id: 0
    @foo
    
    
    id: 1, index: 0
    @bar
    
    
    id: 2, index: 1
    @baz
    
    
    id:3, index:2
    Shape: 2
    from: 0, to: 1, iv index: 0
    from: 1, to: 2, iv index: 1
    from: 2, to: 3, iv index: 2
    Shape: 3
    Shape: 2
    Shape: 4
    @foo
    @bar
    @baz
    frozen
    
    
    id:4
    freeze
    

    View Slide

78. Set Instance Variable Instruction
    Frozen check only on cache misses
    def setinstancevariable iv_name, cache
    
    
    if get_self.frozen?
    
    
    raise "It's frozen!"
    
    
    end
    
    
    if cache.klass == get_self.class && cache.index
    
    
    # CACHE HIT!!
    
    
    # set the instance variable
    
    
    else
    
    
    cache.klass = get_self.class
    
    
    cache.index = get_self.iv_index_table[iv_name]
    
    
    # set the instance variable
    
    
    end
    
    
    end
    Before Shapes
    def setinstancevariable iv_name, cache
    
    
    if cache.from_shape_id == get_self.shape_id
    
    
    # CACHE HIT!!
    
    
    # set the instance variable
    
    
    else
    
    
    if get_self.frozen?
    
    
    raise "It's frozen!"
    
    
    end
    
    
    cache.shape_id = get_self.shape_id
    
    
    # set the instance variable
    
    
    end
    
    
    end
    After Shapes
    

    View Slide

79. Frozen Checks only on
    
    
    Cache Misses
    

    View Slide

80. IV Write Performance Improvement
    require 'harness'
    
    
    class TheClass
    
    
    def initialize
    
    
    @v0 = 1
    
    
    @v1 = 2
    
    
    @v3 = 3
    
    
    @levar = 1
    
    
    end
    
    
    def set_value_loop
    
    
    # 1M
    
    
    i = 0
    
    
    while i < 1000000
    
    
    # 10 times to de-emphasize loop overhead
    
    
    @levar = i
    
    
    @levar = i
    
    
    @levar = i
    
    
    @levar = i
    
    
    @levar = i
    
    
    @levar = i
    
    
    @levar = i
    
    
    @levar = i
    
    
    @levar = i
    
    
    @levar = i
    
    
    i += 1
    
    
    end
    
    
    end
    
    
    end
    
    
    obj = TheClass.new
    
    
    run_benchmark(100) do
    
    
    obj.set_value_loop
    
    
    end
    Micro Benchmark
    before: ruby 3.2.0dev (2022-09-28T14:51:38Z before-shapes a05b261464) [x86_64-linux]
    
    
    after: ruby 3.2.0dev (2022-11-22T05:20:45Z master 20b9d7b9fd) [x86_64-linux]
    
    
    ------- ----------- ---------- ---------- ---------- ------------ -------------
    
    
    bench before (ms) stddev (%) after (ms) stddev (%) before/after after 1st itr
    
    
    setivar 64.0 0.7 53.0 2.5 1.21 1.19
    
    
    ------- ----------- ---------- ---------- ---------- ------------ -------------
    
    
    Legend:
    
    
    - before/after: ratio of before/after time. Higher is better for after. Above 1
    represents a speedup.
    
    
    - after 1st itr: ratio of before/after time for the first benchmarking iteration
    Results
    21% Faster
    

    View Slide

81. JIT Performance
    

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82. Object Layout
    All objects have 2 common
    fi
    elds: "
    fl
    ags" and "class"
    Basic Object Layout
    Byte Value
    0 Flags (a 64 bit bitmap)
    8 Pointer to Class
    16
    24
    32
    T_OBJECT
    Byte Value
    0 Flags (a 64 bit bitmap)
    8 Pointer to Class
    16 Instance Variable
    24 Instance Variable
    32 Instance Variable
    T_ARRAY
    Byte Value
    0 Flags (a 64 bit bitmap)
    8 Pointer to Class
    16 Array Element
    24 Array Element
    32 Array Element
    

    View Slide

83. Let's Check the Flags Field!
    

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84. 64 bits (width of a pointer)
    

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85. Flags Bitmap Layout
    Bottom 5 bits represent Object Type
    Flags Bitmap
    31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
    Object Type ruby_value_type {
    
    
    RUBY_T_OBJECT = 0x01, /**< @see struct ::RObject */
    
    
    RUBY_T_CLASS = 0x02, /**< @see struct ::RClass and ::rb_cClass */
    
    
    RUBY_T_MODULE = 0x03, /**< @see struct ::RClass and ::rb_cModule */
    
    
    RUBY_T_FLOAT = 0x04, /**< @see struct ::RFloat */
    
    
    RUBY_T_STRING = 0x05, /**< @see struct ::RString */
    
    
    RUBY_T_REGEXP = 0x06, /**< @see struct ::RRegexp */
    
    
    RUBY_T_ARRAY = 0x07, /**< @see struct ::RArray */
    
    
    RUBY_T_HASH = 0x08, /**< @see struct ::RHash */
    
    
    RUBY_T_STRUCT = 0x09, /**< @see struct ::RStruct */
    
    
    RUBY_T_BIGNUM = 0x0a, /**< @see struct ::RBignum */
    
    
    RUBY_T_FILE = 0x0b, /**< @see struct ::RFile */
    
    
    RUBY_T_DATA = 0x0c, /**< @see struct ::RTypedData */
    
    
    RUBY_T_MATCH = 0x0d, /**< @see struct ::RMatch */
    
    
    RUBY_T_COMPLEX = 0x0e, /**< @see struct ::RComplex */
    
    
    RUBY_T_RATIONAL = 0x0f, /**< @see struct ::RRational */
    
    
    }
    

    View Slide

86. Flags Bitmap Layout
    Bottom 12 bits have a common "meaning" (see
    fl
    _type.h)
    Flags Bitmap
    31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
    Object Type
    Object ID has
    been seen?
    Object.new.object_id
    
    
    [].object_id
    

    View Slide

87. Flags Bitmap Layout
    Bottom 12 bits have a common "meaning" (see
    fl
    _type.h)
    Flags Bitmap
    31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
    Object Type
    Object ID has
    been seen?
    Object.new.object_id
    
    
    [].object_id
    

    View Slide

88. Flags Bitmap Layout
    Object Type gives upper bits meaning
    Flags Bitmap
    31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
    Object Type
    Common Stu
    ff
    (see
    fl
    _type.h)
    Object
    Extended?
    Depends on Object Type
    

    View Slide

89. T_OBJECT Extended Layout
    Byte Value
    0 Flags (a 64 bit bitmap)
    8 Pointer to Class
    16 Pointer to Bu
    ff
    er
    24
    32
    IV Array
    Byte Value
    0 Instance Variable
    8 Instance Variable
    16 Instance Variable
    24 Instance Variable
    32 Instance Variable
    ... ...
    class Hello
    
    
    def initialize
    
    
    @foo = 1
    
    
    @bar = 2
    
    
    @baz = 3
    
    
    @hoge = 4
    
    
    end
    
    
    end
    
    
    Hello.new
    
    
    T_OBJECT Layout
    Byte Value
    0 Flags (a 64 bit bitmap)
    8 Pointer to Class
    16 Instance Variable
    24 Instance Variable
    32 Instance Variable
    T_OBJECT Layout
    

    View Slide

90. Flags Bitmap Layout
    Extended Bit means "read from external table"
    Flags Bitmap
    31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
    Object Type
    Common Stu
    ff
    (see
    fl
    _type.h)
    Object
    Extended?
    Depends on Object Type
    

    View Slide

91. JIT Compilation
    JIT compilation must write guards for assumptions
    class Hello
    
    
    def initialize
    
    
    @foo = 1
    
    
    @bar = 2
    
    
    @baz = 3
    
    
    @hoge = 4
    
    
    end
    
    
    def foo
    
    
    @foo + @bar
    
    
    end
    
    
    end
    What is the type?
    Is it embedded or extended?
    Is the IV Qundef?
    Is the Class correct?
    

    View Slide

92. Runtime Check Locations
    We need to test object type, extended bit, IV value
    Flags Bitmap
    31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
    Object Type
    Common Stu
    ff
    (see
    fl
    _type.h)
    Object
    Extended?
    Depends on Object Type
    Byte Value
    0 Flags (a 64 bit bitmap)
    8 Pointer to Class
    16 Instance Variable
    24 Instance Variable
    32 Instance Variable
    Object Type
    Qundef?
    Right
    class?
    

    View Slide

93. Machine Code for reading one IV
    == BLOCK 1/5, ISEQ RANGE [0,3), 93 bytes ======================
    
    
    # getinstancevariable
    
    
    # guard not immediate
    
    
    0x55a658d0a6dd: test qword ptr [r13 + 0x18], 7
    
    
    0x55a658d0a6e5: jne 0x55a660d0a0e5
    
    
    0x55a658d0a6eb: cmp qword ptr [r13 + 0x18], 8
    
    
    0x55a658d0a6f0: jbe 0x55a660d0a0fe
    
    
    0x55a658d0a6f6: mov rax, qword ptr [r13 + 0x18]
    
    
    # guard known class
    
    
    0x55a658d0a6fa: movabs rcx, 0x7fbb2af48f20
    
    
    0x55a658d0a704: cmp qword ptr [rax + 8], rcx
    
    
    0x55a658d0a708: jne 0x55a660d0a117
    
    
    0x55a658d0a70e: mov rax, qword ptr [r13 + 0x18]
    
    
    0x55a658d0a712: cmp qword ptr [rax + 0x10], 0
    
    
    0x55a658d0a717: jbe 0x55a660d0a0cc
    
    
    # guard embedded getivar
    
    
    0x55a658d0a71d: test word ptr [rax], 0x2000
    
    
    0x55a658d0a722: je 0x55a660d0a130
    
    
    0x55a658d0a728: cmp qword ptr [rax + 0x18], 0x34
    
    
    0x55a658d0a72d: mov ecx, 8
    
    
    0x55a658d0a732: cmovne rcx, qword ptr [rax + 0x18]
    
    
    0x55a658d0a737: mov qword ptr [rbx], rcx
    Generated Machine Code
    

    View Slide

94. Use Shapes to
    
    
    Eliminate Checks
    

    View Slide

95. Shape ID Storage
    Shape id is stored in the upper 32 bits
    Flags Bitmap
    31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
    Object Type
    Common Stu
    ff
    (see
    fl
    _type.h)
    Depends on Object Type
    Shape ID
    

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96. Class Check Isn't Necessary
    Shapes are independent of class
    Flags Bitmap
    31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
    Object Type
    Common Stu
    ff
    (see
    fl
    _type.h)
    Object
    Extended?
    Depends on Object Type
    Byte Value
    0 Flags (a 64 bit bitmap)
    8 Pointer to Class
    16 Instance Variable
    24 Instance Variable
    32 Instance Variable
    Object Type
    Qundef?
    Right
    class?
    Shape ID
    

    View Slide

97. Handling "Undefined" Instance Variables
    Shapes care about IV set order
    class Hello
    
    
    def initialize(set_bar)
    
    
    @foo = 1
    
    
    @bar = 2 if set_bar
    
    
    @baz = 3
    
    
    end
    
    
    def foo
    
    
    if !instance_variable_defined?(:@bar)
    
    
    puts "oh!"
    
    
    end
    
    
    @foo + @bar.to_i
    
    
    end
    
    
    end
    
    
    p Hello.new(true).foo # => 3
    
    
    p Hello.new(false).foo # => 1
    Root
    
    
    id: 0
    @foo
    
    
    id: 1
    @bar
    
    
    id: 2
    @baz
    
    
    id: 3
    @baz
    
    
    id: 4
    Shape 3
    Shape 4
    

    View Slide

98. Handling "Undefined" Instance Variables
    Shape 3 has a "bar" instance variable
    class Hello
    
    
    def initialize(set_bar)
    
    
    @foo = 1
    
    
    @bar = 2 if set_bar
    
    
    @baz = 3
    
    
    end
    
    
    def foo
    
    
    if !instance_variable_defined?(:@bar)
    
    
    puts "oh!"
    
    
    end
    
    
    @foo + @bar.to_i
    
    
    end
    
    
    end
    
    
    p Hello.new(true).foo # => 3
    
    
    p Hello.new(false).foo # => 1
    Shape 3
    Root
    
    
    id: 0
    @foo
    
    
    id: 1
    @bar
    
    
    id: 2
    @baz
    
    
    id: 3
    @baz
    
    
    id: 4
    

    View Slide

99. Handling "Undefined" Instance Variables
    Shape 4 doesn't have a "bar" instance variable
    class Hello
    
    
    def initialize(set_bar)
    
    
    @foo = 1
    
    
    @bar = 2 if set_bar
    
    
    @baz = 3
    
    
    end
    
    
    def foo
    
    
    if !instance_variable_defined?(:@bar)
    
    
    puts "oh!"
    
    
    end
    
    
    @foo + @bar.to_i
    
    
    end
    
    
    end
    
    
    p Hello.new(true).foo # => 3
    
    
    p Hello.new(false).foo # => 1
    Shape 4
    Root
    
    
    id: 0
    @foo
    
    
    id: 1
    @bar
    
    
    id: 2
    @baz
    
    
    id: 3
    @baz
    
    
    id: 4
    

    View Slide

100. Class Check Isn't Necessary
     Shapes are independent of class
     Flags Bitmap
     31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
     Object Type
     Common Stu
     ff
     (see
     fl
     _type.h)
     Object
     Extended?
     Depends on Object Type
     Byte Value
     0 Flags (a 64 bit bitmap)
     8 Pointer to Class
     16 Instance Variable
     24 Instance Variable
     32 Instance Variable
     Object Type
     Qundef?
     Shape ID
     

     View Slide

101. Multiple Possible Layouts
     Objects can vary in width, so there are 2 possible layouts
     class Hello
     
     
     def initialize
     
     
     @foo = 1
     
     
     @bar = 2
     
     
     @baz = 3
     
     
     end
     
     
     def foo
     
     
     @foo + @bar
     
     
     end
     
     
     end
     
     
     Hello.new
     Embedded Layout
     Byte Value
     0 Flags (a 64 bit bitmap)
     8 Pointer to Class
     16 1
     24 2
     32 3
     Extended Layout
     Byte Value
     0 Flags (a 64 bit bitmap)
     8 Pointer to Class
     16 Pointer to Bu
     ff
     er
     24
     32
     IV Array
     Byte Value
     0 1
     8 2
     16 3
     24 ...
     32 ...
     ... ...
     

     View Slide

102. Multiple Possible Layouts
     "Extending" adds a shape transition
     class Hello
     
     
     def initialize
     
     
     @foo = 1
     
     
     @bar = 2
     
     
     @baz = 3
     
     
     end
     
     
     def foo
     
     
     @foo + @bar
     
     
     end
     
     
     end
     
     
     Hello.new
     Extended Layout
     Byte Value
     0 Flags
     8 Class
     16
     24
     Byte Val
     0 1
     8 2
     16 3
     24 ...
     32 ...
     ... ...
     IV Ptr
     1
     2
     Root
     
     
     id: 0
     @bar
     
     
     id: 2
     @foo
     
     
     id: 1
     EXTEND
     
     
     id: 3
     @baz
     
     
     id: 4
     Shape 4
     

     View Slide

103. Multiple Possible Layouts
     "Extending" adds a shape transition
     class Hello
     
     
     def initialize
     
     
     @foo = 1
     
     
     @bar = 2
     
     
     @baz = 3
     
     
     end
     
     
     def foo
     
     
     @foo + @bar
     
     
     end
     
     
     end
     
     
     Hello.new
     Root
     
     
     id: 0
     @bar
     
     
     id: 2
     @foo
     
     
     id: 1
     EXTEND
     
     
     id: 3
     @baz
     
     
     id: 4
     @baz
     
     
     id: 5
     Embedded Layout
     Byte Value
     0 Flags
     8 Class
     16
     24
     32
     2
     3
     1
     Shape 5
     

     View Slide

104. Different Layouts Have Different Shapes
     JIT Compiler can di
     ff
     erentiate based on shape id
     class Hello
     
     
     def initialize
     
     
     @foo = 1
     
     
     @bar = 2
     
     
     @baz = 3
     
     
     end
     
     
     def foo
     
     
     @foo + @bar
     
     
     end
     
     
     end
     
     
     Hello.new
     Root
     
     
     id: 0
     @bar
     
     
     id: 2
     @foo
     
     
     id: 1
     EXTEND
     
     
     id: 3
     @baz
     
     
     id: 4
     @baz
     
     
     id: 5
     Embedded Layout
     Byte Value
     0 Flags
     8 Class
     16 1
     24 2
     32 3
     Extended Layout
     Byte Value
     0 Flags
     8 Class
     16 PTR
     24
     Byte Val
     0 1
     8 2
     16 3
     24 ...
     32 ...
     ... ...
     

     View Slide

105. Extended Check Isn't Necessary
     Shapes di
     ff
     er depending on embedded vs extended
     Flags Bitmap
     31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
     Object Type
     Common Stu
     ff
     (see
     fl
     _type.h)
     Object
     Extended?
     Depends on Object Type
     Object Type
     Shape ID
     

     View Slide

106. Different Types, Same Shape
     Di
     ff
     erent types can have the same shape, but IV storage is di
     ff
     erent
     class Hello
     
     
     def initialize
     
     
     @foo = 1
     
     
     @bar = 2
     
     
     @baz = 3
     
     
     end
     
     
     end
     
     
     Hello.new
     
     
     ary = []
     
     
     ary.instance_variable_set(:@foo, 4)
     
     
     ary.instance_variable_set(:@bar, 5)
     
     
     ary.instance_variable_set(:@baz, 6)
     
     
     ary
     Sample Code Shape Tree
     Root
     
     
     id: 0
     @foo
     
     
     id: 1
     @bar
     
     
     id: 2
     @baz
     
     
     id: 3
     Shape 3
     Shape 3
     

     View Slide

107. Different Types Store Instance
     Variables Differently.
     

     View Slide

108. Assign Shape at Allocation Time
     When a T_OBJECT is allocated, immediately set a new shape
     class Hello
     
     
     def initialize
     
     
     @foo = 1
     
     
     @bar = 2
     
     
     @baz = 3
     
     
     end
     
     
     end
     
     
     Hello.new
     
     
     ary = []
     
     
     ary.instance_variable_set(:@foo, 4)
     
     
     ary.instance_variable_set(:@bar, 5)
     
     
     ary.instance_variable_set(:@baz, 6)
     
     
     ary
     Sample Code Shape Tree
     Root
     
     
     id: 0
     Shape 4
     Shape 7
     T_OBJECT
     
     
     id: 1
     @foo
     
     
     id: 2
     @bar
     
     
     id: 3
     @baz
     
     
     id: 4
     @foo
     
     
     id: 5
     @bar
     
     
     id: 6
     @baz
     
     
     id: 7
     

     View Slide

109. Object Type Check Isn't Necessary
     Shapes di
     ff
     er depending on object type
     Flags Bitmap
     31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
     Object Type
     Common Stu
     ff
     (see
     fl
     _type.h)
     Depends on Object Type
     Object Type
     Shape ID
     

     View Slide

110. Only Shape ID Check is Required
     

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111. JIT Code Comparison
     Machine code for reading 1 instance variable
     == BLOCK 1/5, ISEQ RANGE [0,3), 93 bytes ======================
     
     
     # getinstancevariable
     
     
     # guard not immediate
     
     
     0x55ce5998b6dd: test qword ptr [r13 + 0x18], 7
     
     
     0x55ce5998b6e5: jne 0x55ce6198b0e5
     
     
     0x55ce5998b6eb: cmp qword ptr [r13 + 0x18], 8
     
     
     0x55ce5998b6f0: jbe 0x55ce6198b0fe
     
     
     0x55ce5998b6f6: mov rax, qword ptr [r13 + 0x18]
     
     
     # guard known class
     
     
     0x55ce5998b6fa: movabs rcx, 0x7f09fd1e8f30
     
     
     0x55ce5998b704: cmp qword ptr [rax + 8], rcx
     
     
     0x55ce5998b708: jne 0x55ce6198b117
     
     
     0x55ce5998b70e: mov rax, qword ptr [r13 + 0x18]
     
     
     0x55ce5998b712: cmp qword ptr [rax + 0x10], 0
     
     
     0x55ce5998b717: jbe 0x55ce6198b0cc
     
     
     # guard embedded getivar
     
     
     0x55ce5998b71d: test word ptr [rax], 0x2000
     
     
     0x55ce5998b722: je 0x55ce6198b130
     
     
     0x55ce5998b728: cmp qword ptr [rax + 0x18], 0x34
     
     
     0x55ce5998b72d: mov ecx, 8
     
     
     0x55ce5998b732: cmovne rcx, qword ptr [rax + 0x18]
     
     
     0x55ce5998b737: mov qword ptr [rbx], rcx
     Before Object Shapes
     == BLOCK 1/5, ISEQ RANGE [0,3), 40 bytes ======================
     
     
     # getinstancevariable
     
     
     0x5594850ba13a: mov rax, qword ptr [r13 + 0x18]
     
     
     # guard object is heap
     
     
     0x5594850ba13e: test al, 7
     
     
     0x5594850ba141: jne 0x5594850bc090
     
     
     0x5594850ba147: cmp rax, 0
     
     
     0x5594850ba14b: je 0x5594850bc090
     
     
     # guard shape
     
     
     0x5594850ba151: cmp dword ptr [rax + 4], 0x19
     
     
     0x5594850ba155: jne 0x5594850bc0a9
     
     
     0x5594850ba15b: mov rax, qword ptr [rax + 0x10]
     
     
     0x5594850ba15f: mov qword ptr [rbx], rax
     After Object Shapes
     

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112. JIT Code Comparison
     Machine code for reading 1 instance variable
     == BLOCK 1/5, ISEQ RANGE [0,3), 93 bytes ======================
     
     
     # getinstancevariable
     
     
     # guard not immediate
     
     
     0x55ce5998b6dd: test qword ptr [r13 + 0x18], 7
     
     
     0x55ce5998b6e5: jne 0x55ce6198b0e5
     
     
     0x55ce5998b6eb: cmp qword ptr [r13 + 0x18], 8
     
     
     0x55ce5998b6f0: jbe 0x55ce6198b0fe
     
     
     0x55ce5998b6f6: mov rax, qword ptr [r13 + 0x18]
     
     
     # guard known class
     
     
     0x55ce5998b6fa: movabs rcx, 0x7f09fd1e8f30
     
     
     0x55ce5998b704: cmp qword ptr [rax + 8], rcx
     
     
     0x55ce5998b708: jne 0x55ce6198b117
     
     
     0x55ce5998b70e: mov rax, qword ptr [r13 + 0x18]
     
     
     0x55ce5998b712: cmp qword ptr [rax + 0x10], 0
     
     
     0x55ce5998b717: jbe 0x55ce6198b0cc
     
     
     # guard embedded getivar
     
     
     0x55ce5998b71d: test word ptr [rax], 0x2000
     
     
     0x55ce5998b722: je 0x55ce6198b130
     
     
     0x55ce5998b728: cmp qword ptr [rax + 0x18], 0x34
     
     
     0x55ce5998b72d: mov ecx, 8
     
     
     0x55ce5998b732: cmovne rcx, qword ptr [rax + 0x18]
     
     
     0x55ce5998b737: mov qword ptr [rbx], rcx
     Before Object Shapes
     == BLOCK 1/5, ISEQ RANGE [0,3), 40 bytes ======================
     
     
     # getinstancevariable
     
     
     0x5594850ba13a: mov rax, qword ptr [r13 + 0x18]
     
     
     # guard object is heap
     
     
     0x5594850ba13e: test al, 7
     
     
     0x5594850ba141: jne 0x5594850bc090
     
     
     0x5594850ba147: cmp rax, 0
     
     
     0x5594850ba14b: je 0x5594850bc090
     
     
     # guard shape
     
     
     0x5594850ba151: cmp dword ptr [rax + 4], 0x19
     
     
     0x5594850ba155: jne 0x5594850bc0a9
     
     
     After Object Shapes
     Make sure it's
     shape 0x19
     

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113. JIT Code Comparison
     Machine code for reading 1 instance variable
     == BLOCK 1/5, ISEQ RANGE [0,3), 93 bytes ======================
     
     
     # getinstancevariable
     
     
     # guard not immediate
     
     
     0x55ce5998b6dd: test qword ptr [r13 + 0x18], 7
     
     
     0x55ce5998b6e5: jne 0x55ce6198b0e5
     
     
     0x55ce5998b6eb: cmp qword ptr [r13 + 0x18], 8
     
     
     0x55ce5998b6f0: jbe 0x55ce6198b0fe
     
     
     0x55ce5998b6f6: mov rax, qword ptr [r13 + 0x18]
     
     
     # guard known class
     
     
     0x55ce5998b6fa: movabs rcx, 0x7f09fd1e8f30
     
     
     0x55ce5998b704: cmp qword ptr [rax + 8], rcx
     
     
     0x55ce5998b708: jne 0x55ce6198b117
     
     
     0x55ce5998b70e: mov rax, qword ptr [r13 + 0x18]
     
     
     0x55ce5998b712: cmp qword ptr [rax + 0x10], 0
     
     
     0x55ce5998b717: jbe 0x55ce6198b0cc
     
     
     # guard embedded getivar
     
     
     0x55ce5998b71d: test word ptr [rax], 0x2000
     
     
     0x55ce5998b722: je 0x55ce6198b130
     
     
     0x55ce5998b728: cmp qword ptr [rax + 0x18], 0x34
     
     
     0x55ce5998b72d: mov ecx, 8
     
     
     0x55ce5998b732: cmovne rcx, qword ptr [rax + 0x18]
     
     
     0x55ce5998b737: mov qword ptr [rbx], rcx
     Before Object Shapes
     == BLOCK 1/5, ISEQ RANGE [0,3), 40 bytes ======================
     
     
     # getinstancevariable
     
     
     0x5594850ba13a: mov rax, qword ptr [r13 + 0x18]
     
     
     # guard object is heap
     
     
     0x5594850ba13e: test al, 7
     
     
     0x5594850ba141: jne 0x5594850bc090
     
     
     0x5594850ba147: cmp rax, 0
     
     
     0x5594850ba14b: je 0x5594850bc090
     
     
     # guard shape
     
     
     0x5594850ba151: cmp dword ptr [rax + 4], 0x19
     
     
     0x5594850ba155: jne 0x5594850bc0a9
     
     
     0x5594850ba15b: mov rax, qword ptr [rax + 0x10]
     
     
     0x5594850ba15f: mov qword ptr [rbx], rax
     After Object Shapes
     Read the IV,
     and push on the
     stack
     

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114. Benchmark Comparison
     Measure the cost of fetching and instance variable
     class TheClass
     
     
     def initialize
     
     
     @v0 = 1
     
     
     @v1 = 2
     
     
     @v3 = 3
     
     
     @levar = 1
     
     
     end
     
     
     def get_value_loop
     
     
     sum = 0
     
     
     # 1M
     
     
     i = 0
     
     
     while i < 1000000
     
     
     # 10 times to de-emphasize loop overhead
     
     
     sum += (@levar +
     
     
     @levar +
     
     
     @levar +
     
     
     @levar +
     
     
     @levar +
     
     
     @levar +
     
     
     @levar +
     
     
     @levar +
     
     
     @levar +
     
     
     @levar)
     
     
     i += 1
     
     
     end
     
     
     return sum
     
     
     end
     
     
     end
     
     
     obj = TheClass.new
     
     
     run_benchmark(100) do
     
     
     obj.get_value_loop
     
     
     end
     

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115. Benchmark Results
     before: ruby 3.2.0dev (2022-09-28T14:51:38Z before-shapes a05b261464) +YJIT [x86_64-linux]
     
     
     after: ruby 3.2.0dev (2022-11-22T05:20:45Z master 20b9d7b9fd) +YJIT [x86_64-linux]
     
     
     ------- ----------- ---------- ---------- ---------- ------------ -------------
     
     
     bench before (ms) stddev (%) after (ms) stddev (%) before/after after 1st itr
     
     
     getivar 17.4 0.5 12.0 0.3 1.45 0.97
     
     
     ------- ----------- ---------- ---------- ---------- ------------ -------------
     
     
     Legend:
     
     
     - before/after: ratio of before/after time. Higher is better for after. Above 1 represents a speedup.
     
     
     - after 1st itr: ratio of before/after time for the first benchmarking iteration.
     45% Speed
     up!
     

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116. Before Shapes: 3.76x
     

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117. After Shapes: 5.42x
     

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118. Future: 32 byte Objects
     

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119. TL;DR
     

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120. Fewer Checks
     

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121. Faster Code
     

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122. Thank You!!
     

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