rust-lang/rust-analyzer

Expression lowering uses unreasonable amount of stack space

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#5317 opened on Jul 11, 2020

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 (3 comments) (0 reactions) (1 assignee)Rust (14,924 stars) (1,726 forks)batch import
A-perfC-enhancementE-hardS-actionablefungood first issue

Description

Our lowering code for expressions is a single giant match, and looks like it consumes a lot of stack space, even in release mode.

See https://github.com/rust-analyzer/rust-analyzer/pull/5316/commits/12d52a726a1e6ca0f6b08343d13d0f6b50d94d8c for some ways to observe this.

It would be nice to optimize this!

Contributor guide

Tech stack
rust
Domain
performancetooling
Issue type
performance
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
5
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
3-5 days
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
blocked
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
mostly clear
Prerequisites
Rust programmingcompiler internalsexpression lowering
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
10
Research direction
Investigate the expression lowering code in the rust analyzer repository, specifically the giant match statement that consumes excessive stack space. Review the referenced commit (12d52a7) in PR #5316 for methods to observe stack usage. Consider splitting the match into separate functions or using boxed closures to reduce stack depth. Look for any existing comments or discussion on the issue for additional context.