Experimental: add ahead-of-time compilation via weval and PBL. #883
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This PR pulls in my work to use "weval", the WebAssembly partial evaluator, to perform ahead-of-time compilation of JavaScript using the PBL interpreter we previously contributed to SpiderMonkey. This work has been merged into the BA fork of SpiderMonkey in bytecodealliance/gecko-dev#45, bytecodealliance/gecko-dev#46, bytecodealliance/gecko-dev#47, bytecodealliance/gecko-dev#48, bytecodealliance/gecko-dev#51, bytecodealliance/gecko-dev#52, bytecodealliance/gecko-dev#53, bytecodealliance/gecko-dev#54, bytecodealliance/gecko-dev#55, and then integrated into StarlingMonkey in bytecodealliance/StarlingMonkey#91. The feature is off by default; it requires a `--enable-experimental-aot` flag to be passed to `js-compute-runtime-cli.js`. This requires a separate build of the engine Wasm module to be used when the flag is passed. This should still be considered experimental until it is tested more widely. The PBL+weval combination passes all jit-tests and jstests in SpiderMonkey, and all integration tests in StarlingMonkey; however, it has not yet been widely tested in real-world scenarios. Initial speedups we are seeing on Octane (CPU-intensive JS benchmarks) are in the 3x-5x range. This is roughly equivalent to the speedup that a native JS engine's "baseline JIT" compiler tier gets over its interpreter, and it uses the same basic techniques -- compiling all polymorphic operations (all basic JS operators) to inline-cache sites that dispatch to stubs depending on types. Further speedups can be obtained eventually by inlining stubs from warmed-up IC chains, but that requires warmup. Important to note is that this compilation approach is *fully ahead-of-time*: it requires no profiling or observation or warmup of user code, and compiles the JS directly to Wasm that does not do any further codegen/JIT at runtime. Thus, it is suitable for the per-request isolation model (new Wasm instance for each request, with no shared state).
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I'm currently debugging the |
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All tests passing now; ready for review I think! |
guybedford
approved these changes
Aug 2, 2024
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This PR pulls in my work to use "weval", the WebAssembly partial evaluator, to perform ahead-of-time compilation of JavaScript using the PBL interpreter we previously contributed to SpiderMonkey. This work has been merged into the BA fork of SpiderMonkey in
bytecodealliance/gecko-dev#45, bytecodealliance/gecko-dev#46, bytecodealliance/gecko-dev#47, bytecodealliance/gecko-dev#48, bytecodealliance/gecko-dev#51, bytecodealliance/gecko-dev#52, bytecodealliance/gecko-dev#53, bytecodealliance/gecko-dev#54, bytecodealliance/gecko-dev#55, and then integrated into StarlingMonkey in bytecodealliance/StarlingMonkey#91.
The feature is off by default; it requires a
--enable-experimental-aotflag to be passed tojs-compute-runtime-cli.js. This requires a separate build of the engine Wasm module to be used when the flag is passed.This should still be considered experimental until it is tested more widely. The PBL+weval combination passes all jit-tests and jstests in SpiderMonkey, and all integration tests in StarlingMonkey; however, it has not yet been widely tested in real-world scenarios.
Initial speedups we are seeing on Octane (CPU-intensive JS benchmarks) are in the 3x-5x range. This is roughly equivalent to the speedup that a native JS engine's "baseline JIT" compiler tier gets over its interpreter, and it uses the same basic techniques -- compiling all polymorphic operations (all basic JS operators) to inline-cache sites that dispatch to stubs depending on types. Further speedups can be obtained eventually by inlining stubs from warmed-up IC chains, but that requires warmup.
Important to note is that this compilation approach is fully ahead-of-time: it requires no profiling or observation or warmup of user code, and compiles the JS directly to Wasm that does not do any further codegen/JIT at runtime. Thus, it is suitable for the per-request isolation model (new Wasm instance for each request, with no shared state).