WebAssembly / WebAssembly/binaryen
Optimize sign checks on i8, i16 etc.
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- Dominant language
- WebAssembly
- Stars
- 8.6k
- Forks
- 885
- Avg merge
- 1d 19h
- Merged PRs (30d)
- 69
Description
E.g.
(select
(local.get $0)
(local.get $1)
(i32.lt_s
(i32.extend8_s
(local.get $2)
)
(i32.const 0)
)
)
=->
(select
(local.get $0)
(local.get $1)
(i32.and
(local.get $2)
(i32.const 128)
)
)
When in a boolean context, doing an extend and then <0 is the same as checking the sign bit of the size we are extending from.
Found by the superoptimizer https://github.com/WebAssembly/binaryen/pull/4994 (for comparison to other findings: rule #2, benefit 49038).
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 with the WebAssembly example in the issue and compare it with the superoptimizer findings in WebAssembly/binaryen pull request 4994. Locate the optimizer entry point that handles sign checks on narrow integers, then add coverage for the shown transformation and verify that the optimized output preserves the boolean result.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- wasm
- Domain
- compilers, performance
- Issue type
- Feature
- Difficulty
- 3/5
- Estimated time
- 1-2 days
- Activity status
- Stale
- Clarity
- Mostly clear
- Newbie friendliness
- 38/100