emscripten-core/emscripten

Compiler information extraction significantly slower compared to vanilla Clang

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#13,004 opened on Dec 10, 2020

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Description

Extracting some basic information (version, target, header search paths) from emcc is significantly slower compared to vanilla Clang. Compare:

$ time { clang++ --version; clang++ -dumpmachine; clang++ -v -x c++ -E - </dev/null; }
real    0m0.029s

$ time { emcc --version; emcc -dumpmachine; emcc -v -x c++ -E - </dev/null; }
real    0m0.266s

Some build systems (e.g., build2) extract this information on the fly (in order to implement high-fidelity change detection) and the slowdown is noticeable. I wonder if anything can done about this?

Contributor guide

Research direction
Profile the emcc invocation to identify bottlenecks. Focus on the Python wrapper and the LLVM backend calls.
Tech stack
cpp
Domain
compilerscli
Issue type
Performance
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
2
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
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Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
Git
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
70