class CustomJSHelperBuilder extends AnyRef

Toolkit to build custom JS helpers that take Wasm inputs, while trying to optimize them directly as JavaScript trees.

The usage scenario for this class is as follows:

val builder = new CustomJSHelperBuilder()

// Add inputs that will be evaluated on the Wasm call site, and whose
// values are then available as `js.Tree`s in the JS helper:
val xRef = builder.addWasmInput(watpe.Int32) {
  // Wasm code evaluated at call site
  fb += wa.LocalGet(someLocal)
}
...

// Build the body of the helper using the above inputs
val helperID = builder.build(watpe.Int32) {
  js.Return(js.BinaryOp(JSBinaryOp.+, xRef, js.IntLiteral(5)))
}

// Call the helper, which consumes the declared inputs and leaves the result on the stack
fb += wa.Call(helperID)

The subclass CustomJSHelperBuilder.WithTreeEval provides even richer capabilities, by allowing to evaluate arbitrary IR Trees as inputs. The builder will optimize the evaluation and transfer from Wasm to JS:

  • Evaluate some trees entirely on the JS side instead of on the Wasm side. This is notably the case for string literals, which commonly appear as method names, and global refs/external imports, which commonly appear as method receivers.
  • For other trees, evaluate them on the Wasm side, but fuse their boxing operation with the Wasm-to-JS interoperability layer, by choosing the best possible Wasm type for the helper function.

When using the WithTreeEval subclass, the user must provide a concrete method to evaluate Trees at call site with a given expected type. In the context of FunctionEmitter, that directly translates to the genTree method.

A typical scenario looks like:

val builder = new CustomJSHelperBuilder.WithTreeEval() {
  protected def evalTreeAtCallSite(tree: Tree, expectedType: Type): Unit = ???
}

// Add inputs that will be evaluated on the JS side if possible, otherwise
// evaluated on the Wasm call site, and whose values are then available as
// `js.Tree`s in the JS helper:
val xRef = builder.addInput(someIRTree)
...

In addition to the input management, CustomJSHelperBuilder provides tools for local name management, and generation of js.ParamDefs for inner functions.

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WithTreeEval
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Instance Constructors

  1. new CustomJSHelperBuilder()(implicit ctx: WasmContext, pos: Position)

Value Members

  1. final def !=(arg0: Any): Boolean
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  2. final def ##(): Int
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  3. final def ==(arg0: Any): Boolean
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  4. def addWasmInput(origName: String, wasmType: Type)(evalValue: ⇒ Unit): VarRef

    Adds an input of an arbitrary Wasm type, to be evaluated on the Wasm stack.

    Adds an input of an arbitrary Wasm type, to be evaluated on the Wasm stack.

    The evalValue must add code to the call site context to evaluate the value on the Wasm site. It is passed as by-name parameter to show intent, but is in fact called immediately.

    returns

    A js.VarRef that can be used in the JS helper to read the input.

  5. final def asInstanceOf[T0]: T0
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  6. def build(resultType: Type)(body: Tree): FunctionID
  7. def clone(): AnyRef
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  11. def genGlobalRef(name: String): VarRef
  12. def genJSNativeLoadSpec(jsNativeLoadSpec: JSNativeLoadSpec): Tree
  13. def genJSParamDef(param: ParamDef): ParamDef
  14. def genJSParamDefs(params: List[ParamDef], restParam: Option[ParamDef]): (List[ParamDef], Option[ParamDef])
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  19. def newLocalIdent(name: LocalName): DelayedIdent
  20. def newLocalIdent(origName: String): DelayedIdent
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