[llvm-dev] [RFC] High-Level Code-Review Documentation Update

Finkel, Hal J. via llvm-dev llvm-dev at lists.llvm.org
Thu Nov 14 19:46:02 PST 2019

Hi, everyone,

I've been fielding an increasing number of questions about how our 
code-review process in LLVM works from people who are new to our 
community, and it's been pointed out to me that our documentation on 
code reviews is both out of date and not as helpful as it could be to 
new developers.


I would like to compose a patch to update this, but before I do that, I 
want to highlight some of my thoughts to get feedback. My intent is to 
capture our community best practices in writing so that people new to 
our community understand our processes and expectations. Here are some 
things that I would like to capture:

  1. You do not need to be an expert in some area of the compiler to 
review patches; it's fine to ask questions about what some piece of code 
is doing. If it's not clear to you what is going on, you're unlikely to 
be the only one. Extra comments and/or test cases can often help (and 
asking for comments in the test cases is fine as well).

  2. If you review a patch, but don't intend for the review process to 
block on your approval, please state that explicitly. Out of courtesy, 
we generally wait on committing a patch until all reviewers are 
satisfied, and if you don't intend to look at the patch again in a 
timely fashion, please communicate that fact in the review.

  3. All comments by reviewers should be addressed by the patch author. 
It is generally expected that suggested changes will be incorporated 
into the next revision of the patch unless the author and/or other 
reviewers can articulate a good reason to do otherwise (and then the 
reviewers must agree). If you suggest changes in a code review, but 
don't wish the suggestion to be interpreted this strongly, please state 
so explicitly.

  4. Reviewers may request certain aspects of a patch to be broken out 
into separate patches for independent review, and also, reviewers may 
accept a patch conditioned on the author providing a follow-up patch 
addressing some particular issue or concern (although no committed patch 
should leave the project in a broken state). Reviewers can also accept a 
patch conditioned on the author applying some set of minor updates prior 
to committing, and when applicable, it is polite for reviewers to do so.

  5. Aim to limit the number of iterations in the review process. For 
example, when suggesting a change, if you want the author to make a 
similar set of changes at other places in the code, please explain the 
requested set of changes so that the author can make all of the changes 
at once. If a patch will require multiple steps prior to approval (e.g., 
splitting, refactoring, posting data from specific performance tests), 
please explain as many of these up front as possible. This allows the 
patch author to make the most-efficient use of his or her time.

  6. Some changes are too large for just a code review. Changes that 
should change the Language Reference (e.g., adding new 
target-independent intrinsics), adding language extensions in Clang, and 
so on, require an RFC on *-dev first. For changes that promise 
significant impact on users and/or downstream code bases, reviewers can 
request an RFC (Request for Comment) achieving consensus before 
proceeding with code review. That having been said, posting initial 
patches can help with discussions on an RFC.

Lastly, the current text reads, "Code reviews are conducted by email on 
the relevant project’s commit mailing list, or alternatively on the 
project’s development list or bug tracker.", and then only later 
mentions Phabricator. I'd like to move Phabricator to be mentioned on 
this line before the other methods.

Please let me know what you think.

Thanks again,


Hal Finkel
Lead, Compiler Technology and Programming Languages
Leadership Computing Facility
Argonne National Laboratory

More information about the llvm-dev mailing list