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@AlexanderPortland AlexanderPortland commented Aug 4, 2025

Internally, Kani uses the call_with_panic_debug_info() function to call closures with a string that explains what they're trying to do, allowing better error messages if they internally panics. However, this function is currently called for every harness we codegen and has to pretty format the harness' function instance--something that calls into rustc internals and takes a non-negligible amount of time.

We should instead accept a closure that can generate debug info, but only when (and if) it's needed.

Results

Based on initial flamegraphing, the formatting passed to call_with_panic_debug_info() went from taking 2.3% of codegen on s2n-codec to not being called a single time (since there are no compiler errors in a typical execution).

This change made a solid 4.6% reduction in the end to end compile time of the standard library (at std commit 177d0fd; assuming #4257, #4259 & #4268 are already merged into Kani).

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 and MIT licenses.

@github-actions github-actions bot added Z-EndToEndBenchCI Tag a PR to run benchmark CI Z-CompilerBenchCI Tag a PR to run benchmark CI labels Aug 4, 2025
@AlexanderPortland AlexanderPortland marked this pull request as ready for review August 6, 2025 00:20
@AlexanderPortland AlexanderPortland requested a review from a team as a code owner August 6, 2025 00:20
@tautschnig tautschnig added this pull request to the merge queue Aug 6, 2025
Merged via the queue into model-checking:main with commit 42951d1 Aug 6, 2025
17 of 18 checks passed
github-merge-queue bot pushed a commit that referenced this pull request Aug 7, 2025
from the autogenerated : 

## What's Changed
* Ensure that contract closures are FnOnce by @vonaka in
#4151
* Adjust sized hierarchy for Kani's memory predicates by @tautschnig in
#4193
* Update to Rust edition 2024 by @tautschnig in
#4197
* `ptr_offset_from`: Replace arithmetic over pointers by offset
arithmetic by @tautschnig in
#4180
* Automatic cargo update to 2025-07-07 by @github-actions[bot] in
#4208
* Bump tests/perf/s2n-quic from `b8f8cca` to `8715fdf` by
@dependabot[bot] in #4209
* Upgrade Rust toolchain to 2025-07-04 by @tautschnig in
#4199
* Upgrade Rust toolchain to 2025-07-10 by @thanhnguyen-aws in
#4215
* Update CBMC dependency to 6.7.1 by @tautschnig in
#4178
* Split compiler flags to avoid dependency recompilation by
@AlexanderPortland in #4211
* Fix the bug that assign clause cannot be inferred for the inner loop
of nested loops by @thanhnguyen-aws in
#4179
* Upgrade Rust toolchain to 2025-07-11 by @thanhnguyen-aws in
#4219
* Automatic toolchain upgrade to nightly-2025-07-12 by
@github-actions[bot] in #4222
* Fix bug: `goto-cc` crash when there are two quantifers in one proof by
@thanhnguyen-aws in #4221
* Automatic toolchain upgrade to nightly-2025-07-13 by
@github-actions[bot] in #4223
* Automatic cargo update to 2025-07-14 by @github-actions[bot] in
#4224
* Cleanup links to issues that have been addressed by @tautschnig in
#4200
* Selectively enable and fix (slow) Tokio tests by @tautschnig in
#4203
* Bump tests/perf/s2n-quic from `32ba87d` to `1cbd879` by
@dependabot[bot] in #4227
* Implement support for Cargo.toml's default-members by @tautschnig in
#4201
* Do not invoke memset with count of zero by @tautschnig in
#4205
* Support bitwuzla, cvc5, z3 as solver attribute values by @tautschnig
in #4218
* Use CBMC's shuffle_vector expression by @tautschnig in
#4204
* Move tests from slow/kani back to regular suite by @tautschnig in
#4202
* Automatic toolchain upgrade to nightly-2025-07-14 by
@github-actions[bot] in #4225
* Enable GitHub Linux/Arm runners in CI by @tautschnig in
#3841
* Automatic cargo update to 2025-07-21 by @github-actions[bot] in
#4231
* Skip codegen for unneeded harnesses by @AlexanderPortland in
#4213
* Strongly type differing compiler args for clarity by
@AlexanderPortland in #4220
* Remove StableMIR ICE workaround by @carolynzech in
#4235
* Fix bug: Kani unwinds loops with contract in generic function (with -Z
loop-contracts) by @thanhnguyen-aws in
#4232
* Automatic cargo update to 2025-07-28 by @github-actions[bot] in
#4238
* Bump tests/perf/s2n-quic from `1cbd879` to `4938450` by
@dependabot[bot] in #4242
* Upgrade Rust toolchain to 2025-07-21 by @tautschnig in
#4241
* Remove `pretty_ty` and use rustc_public's formatter instead by
@tautschnig in #4243
* Upgrade Rust toolchain to 2025-07-24 by @tautschnig in
#4244
* Documentation cleanup of UB detected by Kani by @tautschnig in
#4245
* Upgrade Rust toolchain to 2025-07-29 by @tautschnig in
#4247
* Automatic toolchain upgrade to nightly-2025-07-30 by
@github-actions[bot] in #4253
* Add unstable option prove-safety-only by @tautschnig in
#4239
* Set bits_per_byte in byte_extract expressions by @tautschnig in
#4255
* `KaniAttributes` Path Resolution Refactor by @carolynzech in
#4249
* Automatic toolchain upgrade to nightly-2025-07-31 by
@github-actions[bot] in #4256
* Support contracts & stubs in trait implementations (partial fix) by
@carolynzech in #4250
* [Breaking Changes] Remove unstable list feature and default memory
checks by @carolynzech in
#4258
* Upgrade Rust toolchain to 2025-08-01 by @tautschnig in
#4261
* Autoharness: add support for references by @tautschnig in
#4234
* Turn off debug assertions under `--prove-safety-only` by @tautschnig
in #4262
* Automatic toolchain upgrade to nightly-2025-08-02 by
@github-actions[bot] in #4264
* Automatic toolchain upgrade to nightly-2025-08-03 by
@github-actions[bot] in #4265
* Automatic cargo update to 2025-08-04 by @github-actions[bot] in
#4267
* Automatic toolchain upgrade to nightly-2025-08-04 by
@github-actions[bot] in #4266
* Introduce thread pool for writing goto binaries in parallel by
@AlexanderPortland in #4236
* Major-version update cargo dependencies by @tautschnig in
#4240
* Bump tests/perf/s2n-quic from `4938450` to `8f510f0` by
@dependabot[bot] in #4270
* Automatic toolchain upgrade to nightly-2025-08-05 by
@github-actions[bot] in #4271
* Automatic toolchain upgrade to nightly-2025-08-06 by
@github-actions[bot] in #4272
* Avoid updating irrelevant symbols when handling quantifiers by
@AlexanderPortland in #4268
* Lazily evaluate debug info by @AlexanderPortland in
#4269
* Clone a template `BodyTransformer` to avoid re-initialization by
@AlexanderPortland in #4259
* Ensuring that MIR constants are marked as static consts by @vonaka in
#4233
* Fix release job dependencies by @tautschnig in
#4273

## New Contributors
* @vonaka made their first contribution in
#4151

**Full Changelog**:
kani-0.64.0...kani-0.65.0

---------

Co-authored-by: Zyad Hassan <88045115+zhassan-aws@users.noreply.github.com>
@AlexanderPortland AlexanderPortland deleted the lazy-debug branch August 26, 2025 00:59
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