1571996 - (wasm-tail-calls) [meta] Implement WebAssembly tail calls proposal

Status: NEW

(Core :: JavaScript: WebAssembly, task, P3)

Description

[Andy Wingo [:wingo]]

The WebAssembly tail-call proposal adds two new opcodes to the binary format: return_call and return_call_indirect. These are the same as call and call_indirect, except that they are tail calls.

To make a take call, the engine logically replaces the active stack frame with a call to the callee, instead of pushing a new frame on the stack. In the best case of a call from a function without spilled arguments to a function without spilled arguments, the tail call can be implemented as a simple jmp to the destination code (i.e., skipping any prologue).

The proposal is currently (August 2019) in phase 3 (implementation) of the WebAssembly standardization process. There is an implementation in V8 behind a flag.

Comment 1

[Dan Shearer]

A summary of how this issue is a blocker for Wasm Phase 3/4 progress is here:
https://medium.com/leaningtech/extreme-webassembly-2-the-sad-state-of-webassembly-tail-calls-f5d48ef82a87 in the section "Tail call status on SpiderMonkey/Firefox" . Apart from the technical details, Firefox/SpiderMonkey is one of the two required implementations.

This refers to/depends on the ABI issues in 1572400

Comment 2

[Lars T Hansen [:lth]]

Intent-to-prototype sent: https://groups.google.com/a/mozilla.org/g/dev-platform/c/6BIXCsOmJk8

Comment 3

[Yury Delendik (:yury)]

I'll rebase Lars' tail calls patches to the current tree.