WebAssembly / WebAssembly/binaryen
wasm-opt is 35x slower on windows compared to linux
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Description
See the output produced by building a ~46MB wasm binary and ~47MB JSPI wasm binary using EMCC_DEBUG=2.
On linux:
profiler:DEBUG: block "wasm_opt" took 46.559 seconds
On windows:
profiler:DEBUG: block "wasm_opt" took 1565.294 seconds
Complete build log:
-
windows compile_output.log
-
linux compile_output.log
emcc (Emscripten gcc/clang-like replacement + linker emulating GNU ld) 4.0.10 (b7dc6e5747465580df5984e723b9d1f10d8e804b)
Copyright (C) 2025 the Emscripten authors (see AUTHORS.txt)
This is free and open source software under the MIT license.
There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
wasm-opt version 123 (version_123-168-g8c82b6884)
Contributor guide
First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Research direction
Start by comparing the attached Windows and Linux compile_output.log files and reproducing the ~46MB wasm build with EMCC_DEBUG=2 using emcc 4.0.10 and wasm-opt version 123. Trace the wasm_opt step to isolate the platform-specific slowdown; done means identifying the cause and validating comparable performance after the correction on both platforms.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- wasm
- Domain
- compilers, performance
- Issue type
- Bug
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Activity status
- Stale
- Clarity
- Needs clarification
- Newbie friendliness
- 25/100