🛤 Multi-value

[jfbastien]

This is a tracking issue for a post-MVP feature
It will be updated as the issue progresses.

Topic Multi-value
Champion Andreas Rossberg @rossberg
Status in progress
Phase Implementation phase
Linked issues #937, #667,
Linked repositories github.com/WebAssembly/multi-value)

Details

• Multiple return values for functions:

  • enable unboxing of tuples or structs returned by value
  • efficient compilation of multiple return values

• Multiple results for instructions:

  • enable instructions producing several results (divmod, arithmetics with carry)

• Inputs to blocks:

  • loop labels can have arguments
  • can represent phis on backward edges
  • enable future pick operator to cross block boundary
  • macro definability of instructons with inputs
    • i32.select3 = dup if ... else ... end

[kripken]

Were any numbers presented about how much this can be used in practice? I think previous notes said something about testing in the wasm backend and elsewhere, to see code size etc. Sorry if I missed it in the notes.

[jfbastien]

@kripken I believe you're asking about WebAssembly/meetings#94

[phreda4]

I need this feature for implement a forth compiler to webassembly, without this, I need simulate the stack of parameters.

[binji]

Moved to WebAssembly/proposals#19.