[WIP] Codegen tests

[jswrenn]

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• 👉 [WIP] Codegen tests #3042

Latest Update: v14 — Compare vs v13

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[gemini-code-assist]

Summary of Changes

Hello @jswrenn, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request establishes a new framework for codegen testing within the zerocopy project. It leverages cargo asm and cargo-mca to capture and validate the generated assembly and micro-architectural performance of key zerocopy traits and macros. This system aims to prevent performance regressions and ensure optimal code generation for critical operations by comparing current output against stored reference files.

Highlights

• New Codegen Test Suite: Introduced a new codegen test suite to analyze the generated assembly and micro-architectural performance of zerocopy operations.
• Performance Benchmarks: Added specific benchmarks for TryFromBytes::try_ref_from_bytes and try_transmute_ref! using custom data structures.
• Machine Code Analysis (MCA): Implemented a testing mechanism that uses cargo asm with cargo-mca to generate and compare detailed performance metrics for the compiled code.
• Bless Mode for Expected Output: Included a 'bless' mode, activated via an environment variable, to easily update the expected .mca output files when code generation changes are intentional.

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Changelog

• benches/formats/coco.rs
  • Added a new Rust module defining data structures (C0, C0C0, Packet) used as targets for zerocopy operations in benchmarks.
• benches/try_ref_from_bytes.icelake-server.mca
  • Added expected machine code analysis output for the try_ref_from_bytes benchmark on an Icelake server CPU.
• benches/try_ref_from_bytes.rs
  • Added a new benchmark file for TryFromBytes::try_ref_from_bytes using the coco::Packet structure.
• benches/try_transmute_ref.icelake-server.mca
  • Added expected machine code analysis output for the try_transmute_ref benchmark on an Icelake server CPU.
• benches/try_transmute_ref.rs
  • Added a new benchmark file for try_transmute_ref! using a MinimialViableSource structure.
• tests/codegen.rs
  • Added a new test file that orchestrates the execution of codegen benchmarks, captures their MCA output, and compares it against stored reference files, including a 'bless' functionality.
• tools/update-expected-test-output.sh
  • Updated the script to include the new codegen test suite in its 'bless' operation, allowing for easy updating of expected MCA outputs.

Activity

• The pull request is currently marked as '[WIP]', indicating that it is still under active development by the author.

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[gemini-code-assist]

Code Review

This pull request introduces codegen tests, which is a valuable addition for ensuring the quality and performance of the generated code. My review identified a critical bug in the test runner's logic that would prevent the tests from working as intended, along with a minor typo in a data structure. Once these issues are addressed, the PR will be in great shape.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.87%. Comparing base (4fe6388) to head (b03ee9d).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

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##             main    #3042   +/-   ##
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  Coverage   91.87%   91.87%           
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  Files          20       20           
  Lines        6057     6057           
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  Hits         5565     5565           
  Misses        492      492           

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