wasm-opt is 35x slower on windows compared to linux
Nobody has claimed this yet.
Assessment
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Newbie friendliness
- 25/100
- Issue type
- Bug
- Clarity
- Needs clarification
- Activity status
- Stale
- Tech stack
- wasm
- Domain
- compilers, performance
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.
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)
- Dominant language
- WebAssembly
- Stars
- 8.6k
- Forks
- 885
- Avg merge
- 2d 4h
- Merged PRs (30d)
- 77
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.
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