Add option to use weval, an experimental JS AOT option using partial evaluation.
#541
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guybedford
reviewed
May 26, 2023
| import { isFile } from "./isFile.js"; | ||
| import { isFileOrDoesNotExist } from "./isFileOrDoesNotExist.js"; | ||
| import wizer from "@bytecodealliance/wizer"; | ||
| import weval from "@cfallin/weval"; |
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A standard technique for lazy initialization in JavaScript would be to turn this into a dynamic import() nested into the async code path where Weval is used only.
This PR pulls in some still-experimental work to partially evaluate the SpiderMonkey JS interpreter together with JS scripts, ahead-of-time, to produce compiled code.
It should not yet be considered production-worthy, pending more testing and proving out its stability and performance; but, it is at a point where we believe it should be under a non-default option so that users of the SDK may try it. No guarantees! It may explode your bytecode!
The support works by bundling two builds of the engine Wasm -- with and without the weval intrinsics -- and invoking either Wizer with the "normal" build or weval with the "weval" build, as appropriate. The
--enable-wevaloption selects the latter.I have measured weval showing speedups of ~30% on a Markdown renderer on my machine, and up to ~3.5x on the
cryptobenchmark in the Octane suite (1.83x speedup geomean).This refers to a hash for the
runtime/spidermonkeysubmodule that is in fastly/spidermonkey-wasi-embedding#17; that will need to be merged first (and probably bytecodealliance/gecko-dev#5 before that).I'm not entirely sure about some of the build/packaging integration; that's the bulk of the changes here and will need special review.
The package deps include
@cfallin/weval; if it's preferable, I should probably move the repo to BA and get the appropriate permissions to publish it as@bytecodealliance/weval.