scalar_replacement.js

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// Scalar Replacement of wasm structures.

// A very simple example, this struct should be replaced.

var code =`

(module

  (type $point (struct

    (field $x i32)

    (field $y i32)

))

  (func $test (result i32)

    i32.const 42

    i32.const 11

    struct.new $point

    struct.get $point 1

    return

)`;

let module = new WebAssembly.Module(wasmTextToBinary(code));

instance = new WebAssembly.Instance(module);

// This struct contains a lot of fields and should not be optimized.

code =`

(module

  (type $point (struct

    (field $x i32)

    (field $y1 i32)

    (field $x2 i32)

    (field $y3 i32)

    (field $x4 i32)

    (field $y5 i32)

    (field $x6 i32)

    (field $y7 i32)

    (field $x8 i32)

    (field $y9 i32)

    (field $x10 i32)

    (field $y11 i32)

    (field $x12 i32)

    (field $y13 i32)

    (field $x14 i32)

    (field $y15 i32)

))

  (func $test (result i32)

    i32.const 42

    i32.const 42

    i32.const 42

    i32.const 42

    i32.const 42

    i32.const 42

    i32.const 42

    i32.const 42

    i32.const 42

    i32.const 42

    i32.const 42

    i32.const 42

    i32.const 42

    i32.const 42

    i32.const 42

    i32.const 42

    struct.new $point

    struct.get $point 10

    return

)`;

module = new WebAssembly.Module(wasmTextToBinary(code));

// Using parameters instead of constants to create the struct.

code =`

(module

  (type $point (struct

    (field $x i32)

    (field $y i32)

))

  (func $test (param i32) (param i32) (result i32)

    local.get 0

    local.get 1

    struct.new $point

    struct.get $point 1

    return

)`;

module = new WebAssembly.Module(wasmTextToBinary(code));

instance = new WebAssembly.Instance(module);

// Filling the struct with if/then/else structure around it.

code =`

(module

    (type $point (struct

    (field $x (mut i32))

    (field $y (mut i32))

))

    (func $createAndReturnField (param $cond i32) (result i32)

    (local $s (ref null $point))

    ;; Initialize the struct with some constants

    (struct.new $point (i32.const 12) (i32.const 13))

    (local.set $s)

    (local.get $cond)

    (if (then

        (struct.set $point $x (local.get $s) (i32.const 10))

        (struct.set $point $y (local.get $s) (i32.const 20))

    ) (else

        (struct.set $point $x (local.get $s) (i32.const 30))

        (struct.set $point $y (local.get $s) (i32.const 40))

))

    (struct.get $point $x (local.get $s))

)`;

module = new WebAssembly.Module(wasmTextToBinary(code));

instance = new WebAssembly.Instance(module);

// Same test but with a struct escaping in one of the branches.

// This should prevent the struct to be optimized.

code =`

(module

    (type $point (struct

    (field $x (mut i32))

    (field $y (mut i32))

))

    (global $escapedPoint (mut (ref null $point)) (ref.null $point))

    (func $createAndReturnField (param $cond i32) (result i32)

    (local $s (ref null $point))

    ;; Initialize the struct with some constants

    (struct.new $point (i32.const 12) (i32.const 13))

    (local.set $s)

    (local.get $cond)

    (if (then

        (struct.set $point $x (local.get $s) (i32.const 10))

        (struct.set $point $y (local.get $s) (i32.const 20))

        ;; Storing this struct in a global

        (global.set $escapedPoint (local.get $s))

    ) (else

        (struct.set $point $x (local.get $s) (i32.const 30))

        (struct.set $point $y (local.get $s) (i32.const 40))

))

    (struct.get $point $x (local.get $s))

)`;

module = new WebAssembly.Module(wasmTextToBinary(code));

instance = new WebAssembly.Instance(module);

// In this example, one struct is stored into another one.

// The inner struct is escaping into the other one and will

// not be optimized.

// The outer struct will be optimized by Scalar Replacement.

code =`

(module

  ;; Define a struct type for the inner struct

  (type $InnerStruct (struct

    (field (mut i32))

))

  ;; Define a struct type for the outer struct

  (type $OuterStruct (struct

    (field (mut i32))

    (field (mut i32))

    (field (ref $InnerStruct)) ;; Reference to InnerStruct

))

  ;; Define a function to create and fill both structs.

  (func $createStructs (result (ref $InnerStruct))

    (local $inner (ref $InnerStruct))

    (local $outer (ref $OuterStruct))

    i32.const 42

    struct.new $InnerStruct

    local.set $inner

    i32.const 10

    i32.const 20

    local.get $inner

    struct.new $OuterStruct

    local.set $outer

    ;; Return the inner struct

    local.get $outer

    struct.get $OuterStruct 2

)`;

module = new WebAssembly.Module(wasmTextToBinary(code));

instance = new WebAssembly.Instance(module);