Avoid updating irrelevant symbols when handling quantifiers #4268
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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](model-checking/verify-rust-std@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.
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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 <[email protected]>
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Kani currently has a special
handle_quantifiers()pass after codegen that we need to recursively inline function calls inside quantifier expressions as needed by our hooks. This has to be done for every value in the symbol table, but our current implementation implicitly clones allStmttype values, even if they don't contain any quantifiers and wouldn't need to change. This makes the pass currently take up ~7% of codegen on crates that don't even use quantifiers.Now, the
handle_quantifiers_in_stmt()function just returns an option with a newStmtif inlining was needed, orNoneotherwise, allowing us to avoid any allocations and even needing to insert back into the table in the common case where aStmtdoesn't contain any quantifiers.Results
Flamegraphing shows that this change reduces the
handle_quantifiers()pass from 7.1% to just 0.8% of codegen for thes2n-codeccrate.There was a much less significant change on larger codebases like the standard library, which only saw a <1% improvement in end to end compile time (at std commit 177d0fd, assuming #4257 & #4259 are merged into Kani). That being said, there was a significant 1-7% decrease in codegen time for individual crates of the standard library, so it seems to still make a difference, even if not reflected in e2e time.
By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 and MIT licenses.