Reorder variables in inflate functions to reduce padding holes #1803

Dead2 · 2024-10-09T14:56:43Z

Reorder variables in inflate functions to reduce padding holes due to variable alignment requirements.

This is more a case of doing things the recommended way rather than an optimization.

This is a very very minor change, and while it is probable to have a positive impact on performance, it is so small that I can not reliably benchmark it as it is well within the run-to-run variability.
That said, it seems to trend towards being faster by around 0.02%.

due to variable alignment requirements.

coderabbitai · 2024-10-09T14:56:50Z

Walkthrough

The changes in this pull request primarily optimize the decoding process in the inffast.c and inflate.c files, focusing on state management and memory safety during decompression. Key updates include active declarations of previously commented variables, refinements in the logic for decoding operations, and the introduction of new variables to enhance memory safety. Additionally, the organization of variable declarations in the inflateSync function has been improved for better clarity. Minor formatting and comment adjustments have also been made to enhance readability.

Changes

File(s)	Change Summary
inffast.c	- Active declaration of `window` variable. - Adjusted declaration of `hold`, `lcode`, `dcode`, and `dist` variables to new lines. - Logic refinements for decoding literals and length/distance pairs with added checks for `window`. - Updates to `dist` handling for validity during copying. - Introduction of `extra_safe` variable for memory safety.
inflate.c	- Added `from` variable in `inflate` function. - Reordered declarations of `state`, `in`, and `out` in `inflateSync` function.

Possibly related PRs

Misc inflate cleanup #1797: The changes in this PR involve modifications to the inflate_state structure and its management, which are relevant to the state management enhancements made in the main PR's inflate function.
Compute the "safe" distance properly #1801: This PR focuses on adjustments to the inflate_fast function, specifically related to memory operations, which aligns with the main PR's optimizations in the decoding process and memory safety improvements.

Suggested reviewers

nmoinvaz
KungFuJesus

📜 Recent review details

Configuration used: CodeRabbit UI
Review profile: CHILL

📥 Commits

Files that changed from the base of the PR and between 18af700 and ebd663b.

📒 Files selected for processing (2)

inffast_tpl.h (2 hunks)
inflate.c (3 hunks)

🧰 Additional context used

🔇 Additional comments (7)

inflate.c (3)

480-480: LGTM: Good variable placement for potential performance improvement.

The addition of the unsigned char *from variable is well-placed among similar variables. This reordering aligns with the PR objective and may lead to better memory alignment, potentially reducing padding and improving cache locality.

1309-1310: LGTM: Improved variable ordering for potential performance gain.

The reordering of state, in, and out variables is in line with the PR objective. This change may lead to better memory alignment and potentially reduce padding, which could result in a slight performance improvement without affecting the function's logic.

Line range hint 1-1452: Overall assessment: Focused changes with potential performance benefits.

The changes in this file are minimal and focused, addressing the PR objective of reordering variables to reduce padding holes. The modifications in both the inflate and inflateSync functions are well-considered and may lead to slight performance improvements due to better memory alignment.

While the impact might be small (as mentioned in the PR description, around 0.02% improvement), these changes follow good practices for optimizing memory layout. The modifications don't introduce any logical changes or risks, making this a safe optimization.

inffast_tpl.h (4)

62-62: Approved change to variable declaration of window

Activating the declaration of unsigned char *window; aligns with the objective of reducing padding holes by reordering variables. This change is appropriate and acceptable.

105-105: Approved reordering of hold variable

Moving uint64_t hold; to a new position contributes to efficient memory alignment and padding reduction. This adjustment is consistent with the PR's objectives.

108-109: Approved repositioning of lcode and dcode declarations

Adjusting the positions of code const *lcode; and code const *dcode; helps minimize padding holes due to alignment requirements. This change is acceptable and supports improved memory efficiency.

115-115: Approved reordering of dist variable

Reordering the declaration of unsigned dist; contributes to reducing padding by optimizing variable alignment. This change is appropriate and aligns with the goals of the PR.

Thank you for using CodeRabbit. We offer it for free to the OSS community and would appreciate your support in helping us grow. If you find it useful, would you consider giving us a shout-out on your favorite social media?

❤️ Share

🪧 Tips

Chat

There are 3 ways to chat with CodeRabbit:

Review comments: Directly reply to a review comment made by CodeRabbit. Example:
- I pushed a fix in commit <commit_id>, please review it.
- Generate unit testing code for this file.
- Open a follow-up GitHub issue for this discussion.
Files and specific lines of code (under the "Files changed" tab): Tag @coderabbitai in a new review comment at the desired location with your query. Examples:
- @coderabbitai generate unit testing code for this file.
- @coderabbitai modularize this function.
PR comments: Tag @coderabbitai in a new PR comment to ask questions about the PR branch. For the best results, please provide a very specific query, as very limited context is provided in this mode. Examples:
- @coderabbitai gather interesting stats about this repository and render them as a table. Additionally, render a pie chart showing the language distribution in the codebase.
- @coderabbitai read src/utils.ts and generate unit testing code.
- @coderabbitai read the files in the src/scheduler package and generate a class diagram using mermaid and a README in the markdown format.
- @coderabbitai help me debug CodeRabbit configuration file.

Note: Be mindful of the bot's finite context window. It's strongly recommended to break down tasks such as reading entire modules into smaller chunks. For a focused discussion, use review comments to chat about specific files and their changes, instead of using the PR comments.

CodeRabbit Commands (Invoked using PR comments)

@coderabbitai pause to pause the reviews on a PR.
@coderabbitai resume to resume the paused reviews.
@coderabbitai review to trigger an incremental review. This is useful when automatic reviews are disabled for the repository.
@coderabbitai full review to do a full review from scratch and review all the files again.
@coderabbitai summary to regenerate the summary of the PR.
@coderabbitai resolve resolve all the CodeRabbit review comments.
@coderabbitai configuration to show the current CodeRabbit configuration for the repository.
@coderabbitai help to get help.

Other keywords and placeholders

Add @coderabbitai ignore anywhere in the PR description to prevent this PR from being reviewed.
Add @coderabbitai summary to generate the high-level summary at a specific location in the PR description.
Add @coderabbitai anywhere in the PR title to generate the title automatically.

CodeRabbit Configuration File (`.coderabbit.yaml`)

You can programmatically configure CodeRabbit by adding a .coderabbit.yaml file to the root of your repository.
Please see the configuration documentation for more information.
If your editor has YAML language server enabled, you can add the path at the top of this file to enable auto-completion and validation: # yaml-language-server: $schema=https://coderabbit.ai/integrations/schema.v2.json

Documentation and Community

Visit our Documentation for detailed information on how to use CodeRabbit.
Join our Discord Community to get help, request features, and share feedback.
Follow us on X/Twitter for updates and announcements.

codecov · 2024-10-09T15:03:51Z

Codecov Report

Attention: Patch coverage is 0% with 9 lines in your changes missing coverage. Please review.

Project coverage is 33.20%. Comparing base (18af700) to head (ebd663b).

Files with missing lines	Patch %	Lines
inffast_tpl.h	0.00%	5 Missing ⚠️
inflate.c	0.00%	4 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #1803      +/-   ##
===========================================
- Coverage    33.26%   33.20%   -0.06%     
===========================================
  Files           66       66              
  Lines         5481     5481              
  Branches      1222     1222              
===========================================
- Hits          1823     1820       -3     
  Misses        3399     3399              
- Partials       259      262       +3

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

KungFuJesus

Even if the performance wins are only theoretical, reducing the memory footprint is always a plus, especially when it's no cost like this.

Reorder variables in inflate functions to reduce padding holes

ebd663b

due to variable alignment requirements.

Dead2 added the cleanup Improving maintainability or removing code. label Oct 9, 2024

Dead2 requested review from KungFuJesus and nmoinvaz October 9, 2024 14:56

nmoinvaz approved these changes Oct 9, 2024

View reviewed changes

KungFuJesus approved these changes Oct 9, 2024

View reviewed changes

Dead2 merged commit dae668d into develop Oct 10, 2024
279 of 290 checks passed

Dead2 deleted the inflate-padding-cleanup2 branch October 10, 2024 11:22

coderabbitai bot mentioned this pull request Oct 15, 2024

Simplify inflate fast by dispatching to chunkmemset for all chunkcopy cases #1802

Merged

This was referenced Oct 28, 2024

Make an AVX512 inflate fast with low cost masked writes #1805

Merged

Add support for sending "assume" hints to compilers #1808

Draft

Dead2 mentioned this pull request Dec 31, 2024

2.2.3 Release #1838

Merged

coderabbitai bot mentioned this pull request Feb 7, 2025

Fix shift overflow in inflate and send_code. #1859

Merged

coderabbitai bot mentioned this pull request Aug 18, 2025

Remove here pointer in inflate_fast. #1953

Closed

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

Uh oh!

Uh oh!

Reorder variables in inflate functions to reduce padding holes #1803

Reorder variables in inflate functions to reduce padding holes #1803

Uh oh!

Dead2 commented Oct 9, 2024 •

edited

Loading

Uh oh!

coderabbitai bot commented Oct 9, 2024 •

edited

Loading

Chat

CodeRabbit Commands (Invoked using PR comments)

Other keywords and placeholders

CodeRabbit Configuration File (`.coderabbit.yaml`)

Documentation and Community

Uh oh!

codecov bot commented Oct 9, 2024 •

edited

Loading

Uh oh!

KungFuJesus left a comment

Uh oh!

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

4 participants

Uh oh!

Reorder variables in inflate functions to reduce padding holes #1803

Reorder variables in inflate functions to reduce padding holes #1803

Uh oh!

Conversation

Dead2 commented Oct 9, 2024 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

coderabbitai bot commented Oct 9, 2024 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Walkthrough

Changes

Possibly related PRs

Suggested reviewers

Chat

CodeRabbit Commands (Invoked using PR comments)

Other keywords and placeholders

CodeRabbit Configuration File (.coderabbit.yaml)

Documentation and Community

Uh oh!

codecov bot commented Oct 9, 2024 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Codecov Report

Uh oh!

KungFuJesus left a comment

Choose a reason for hiding this comment

Uh oh!

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

4 participants

Dead2 commented Oct 9, 2024 •

edited

Loading

coderabbitai bot commented Oct 9, 2024 •

edited

Loading

CodeRabbit Configuration File (`.coderabbit.yaml`)

codecov bot commented Oct 9, 2024 •

edited

Loading