test: Fix the modarith benchmarks measuring dead code - #1663
Merged
Conversation
Contributor
Codecov Report✅ All modified and coverable lines are covered by tests. Additional details and impacted files@@ Coverage Diff @@
## master #1663 +/- ##
=======================================
Coverage 97.72% 97.72%
=======================================
Files 171 171
Lines 15636 15636
Branches 3616 3616
=======================================
Hits 15280 15280
Misses 269 269
Partials 87 87
Flags with carried forward coverage won't be shown. Click here to find out more.
🚀 New features to boost your workflow:
|
There was a problem hiding this comment.
Pull request overview
Prevents compilers from eliminating modular arithmetic benchmark loops.
Changes:
- Consumes final addition, subtraction, and multiplication results with
DoNotOptimize().
💡 Add a code-review agent skill or configure MCP servers for context-aware, tailored reviews. Learn more in the docs.
The benchmarked values are unused after the loop, so the compiler is free to delete the loop body: the addition and subtraction benchmarks measured an empty loop. The multiplication survived only because its call was not inlined. Consume the final values with DoNotOptimize.
chfast
force-pushed
the
test/modarith-bench-dce
branch
from
August 18, 2026 21:25
34ee143 to
8b11ea6
Compare
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Add this suggestion to a batch that can be applied as a single commit.This suggestion is invalid because no changes were made to the code.Suggestions cannot be applied while the pull request is closed.Suggestions cannot be applied while viewing a subset of changes.Only one suggestion per line can be applied in a batch.Add this suggestion to a batch that can be applied as a single commit.Applying suggestions on deleted lines is not supported.You must change the existing code in this line in order to create a valid suggestion.Outdated suggestions cannot be applied.This suggestion has been applied or marked resolved.Suggestions cannot be applied from pending reviews.Suggestions cannot be applied on multi-line comments.Suggestions cannot be applied while the pull request is queued to merge.Suggestion cannot be applied right now. Please check back later.
The benchmarked values are unused after the loop, so the compiler is free to delete the loop body.
For addition and subtraction it does exactly that, and the benchmarks have been reporting the cost
of an empty loop. Consuming the final values with
DoNotOptimize()keeps the chain alive withoutadding anything inside the loop.
modarith_add<bn254>modarith_sub<bn254>modarith_mul<bn254>Only the multiplication was surviving, and only because its call was not inlined — which makes it
fragile rather than correct. It is the reason this comes first: with a compile-time modulus the
multiplication does get inlined, and would then be eliminated too.