[codegen] Make codegen tests even more stressful.

[jswrenn]

For TryFromBytes and FromBytes tests:

• Alignment is now 4.
• Minimum size is now 12.
• Trailing padding may be dynamically present.

For transmute_ref! and try_transmute_ref!:

• Metadata fixup required.

---

• 　  [codegen] Test and document codegen under different layouts #3085
• 👉 [codegen] Make codegen tests even more stressful. #3083

Latest Update: v6 — Compare vs v5

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[gemini-code-assist]

Summary of Changes

Hello, 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 significantly enhances the robustness of zerocopy's code generation tests by introducing more challenging scenarios for TryFromBytes, FromBytes, and transmute_ref! macros. The changes aim to simulate "worst-case" conditions, ensuring that the library's traits and macros correctly handle complex memory layouts, alignment requirements, and dynamic sizing, including necessary runtime pointer metadata adjustments. This leads to more comprehensive validation of the generated code's correctness and efficiency.

Highlights

• Enhanced Codegen Tests for TryFromBytes and FromBytes: The codegen tests for TryFromBytes and FromBytes traits have been made more stringent. The Packet struct used in these benchmarks now requires an alignment of 4, a minimum size of 12 bytes, and supports dynamically present trailing padding. This aims to simulate more 'stressful' worst-case scenarios for the zerocopy library.
• Metadata Fixup for transmute_ref! and try_transmute_ref!: The benchmarks for transmute_ref! and try_transmute_ref! macros now specifically test scenarios where pointer metadata fixup is required at runtime. This is achieved by using a source type with a larger fixed header size than the destination type, ensuring the macros correctly adjust metadata.
• Updated Documentation: Documentation for TryFromBytes, FromBytes, transmute_ref!, and try_transmute_ref! has been updated to clearly describe these new, more complex test conditions and the implications for generated code, including runtime checks and metadata adjustments.
• New Benchmark Format File: A new file, benches/formats/coco_no_padding.rs, was introduced. This file defines a Packet struct with the original, less stringent layout, specifically for use in the transmute_ref benchmarks to facilitate the metadata fixup testing.

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Changelog

• benches/formats/coco.rs
  • Updated Packet struct alignment from 2 to 4
  • Added a milk: u8 field to Packet
  • Changed temperature field type from u8 to [u8; 5]
  • Increased marshmallows array size from [u8; 2] to [u8; 3]
• benches/formats/coco_no_padding.rs
  • Added a new file defining C0C0 enum and Packet struct with original alignment and field types for transmute_ref benchmarks
• benches/ref_from_bytes.x86-64
  • Modified assembly code to implement new alignment and size checks for ref_from_bytes benchmark
• benches/ref_from_bytes.x86-64.mca
  • Updated performance metrics to reflect changes in the ref_from_bytes benchmark
• benches/ref_from_bytes_with_elems.x86-64
  • Modified assembly code to implement new alignment and size checks for ref_from_bytes_with_elems benchmark
• benches/ref_from_bytes_with_elems.x86-64.mca
  • Updated performance metrics to reflect changes in the ref_from_bytes_with_elems benchmark
• benches/ref_from_prefix.x86-64
  • Modified assembly code to implement new alignment and size checks for ref_from_prefix benchmark
• benches/ref_from_prefix.x86-64.mca
  • Updated performance metrics to reflect changes in the ref_from_prefix benchmark
• benches/ref_from_prefix_with_elems.x86-64
  • Modified assembly code to implement new alignment and size checks for ref_from_prefix_with_elems benchmark
• benches/ref_from_prefix_with_elems.x86-64.mca
  • Updated performance metrics to reflect changes in the ref_from_prefix_with_elems benchmark
• benches/ref_from_suffix.x86-64
  • Modified assembly code to implement new alignment and size checks for ref_from_suffix benchmark
• benches/ref_from_suffix.x86-64.mca
  • Updated performance metrics to reflect changes in the ref_from_suffix benchmark
• benches/ref_from_suffix_with_elems.x86-64
  • Modified assembly code to implement new alignment and size checks for ref_from_suffix_with_elems benchmark
• benches/ref_from_suffix_with_elems.x86-64.mca
  • Updated performance metrics to reflect changes in the ref_from_suffix_with_elems benchmark
• benches/transmute_ref.rs
  • Updated format module path to coco_no_padding.rs
  • Increased MinimalViableSource header size from [u8; 4] to [u8; 6]
• benches/transmute_ref.x86-64
  • Modified assembly code to adjust pointer metadata for transmute_ref benchmark
• benches/transmute_ref.x86-64.mca
  • Updated performance metrics to reflect changes in the transmute_ref benchmark
• benches/try_ref_from_bytes.x86-64
  • Modified assembly code to implement new alignment and size checks for try_ref_from_bytes benchmark
• benches/try_ref_from_bytes.x86-64.mca
  • Updated performance metrics to reflect changes in the try_ref_from_bytes benchmark
• benches/try_ref_from_bytes_with_elems.x86-64
  • Modified assembly code to implement new alignment and size checks for try_ref_from_bytes_with_elems benchmark
• benches/try_ref_from_bytes_with_elems.x86-64.mca
  • Updated performance metrics to reflect changes in the try_ref_from_bytes_with_elems benchmark
• benches/try_ref_from_prefix.x86-64
  • Modified assembly code to implement new alignment and size checks for try_ref_from_prefix benchmark
• benches/try_ref_from_prefix.x86-64.mca
  • Updated performance metrics to reflect changes in the try_ref_from_prefix benchmark
• benches/try_ref_from_prefix_with_elems.x86-64
  • Modified assembly code to implement new alignment and size checks for try_ref_from_prefix_with_elems benchmark
• benches/try_ref_from_prefix_with_elems.x86-64.mca
  • Updated performance metrics to reflect changes in the try_ref_from_prefix_with_elems benchmark
• benches/try_ref_from_suffix.x86-64
  • Modified assembly code to implement new alignment and size checks for try_ref_from_suffix benchmark
• benches/try_ref_from_suffix.x86-64.mca
  • Updated performance metrics to reflect changes in the try_ref_from_suffix benchmark
• benches/try_ref_from_suffix_with_elems.x86-64
  • Modified assembly code to implement new alignment and size checks for try_ref_from_suffix_with_elems benchmark
• benches/try_ref_from_suffix_with_elems.x86-64.mca
  • Updated performance metrics to reflect changes in the try_ref_from_suffix_with_elems benchmark
• src/lib.rs
  • Updated documentation for TryFromBytes and FromBytes traits to reflect more stringent test conditions, including alignment, minimum length, and total length divisibility for worst-case benchmarks
• src/macros.rs
  • Updated documentation for transmute_ref! and try_transmute_ref! to clarify runtime pointer metadata adjustment due to differing fixed header sizes

Activity

• No human activity has been recorded on this pull request since its creation.

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[gemini-code-assist]

Code Review

This pull request strengthens the codegen tests by introducing more complex data structures with stricter alignment and size requirements. The changes are well-aligned with the goal of making the tests more stressful. The updates to generated assembly, performance benchmarks, and documentation are all consistent with these changes. I have a couple of minor suggestions to improve the grammar in the updated documentation for better clarity.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.87%. Comparing base (daa1971) to head (5eafa06).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3083   +/-   ##
=======================================
  Coverage   91.87%   91.87%           
=======================================
  Files          20       20           
  Lines        6057     6057           
=======================================
  Hits         5565     5565           
  Misses        492      492           

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