Optimize reachability with non-mutating global passes #4177
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For context, I intentionally implemented this as separate traits rather than having |
tautschnig
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Jun 27, 2025
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I actually just switched this to use the same boolean strategy as |
Different implementation now, so old review doesn't appy; I can do the re-review next week.
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Auto generated release notes: ## What's Changed * Edit quantifiers' documentation. by @thanhnguyen-aws in #4142 * Fix the bug of using multiple hidden variables for the prev of the same Expr by @thanhnguyen-aws in #4150 * Remove `assess` subcommand by @carolynzech in #4111 * Optimize goto binary exporting in `cprover_bindings` by @AlexanderPortland in #4148 * Add the option to generate performance flamegraphs by @AlexanderPortland in #4138 * Fix the bug: Static union values can panic Kani by @thanhnguyen-aws in #4112 * Update toolchain to 2025-06-13 by @carolynzech in #4152 * Automatic cargo update to 2025-06-16 by @github-actions in #4156 * Major-version update cargo dependencies by @tautschnig in #4158 * Upgrade Rust toolchain to 2025-06-16 by @tautschnig in #4157 * Bump tests/perf/s2n-quic from `3129ad5` to `c6e694e` by @dependabot in #4160 * Bump tests/perf/s2n-quic from `c6e694e` to `b1b5bf8` by @dependabot in #4164 * Upgrade Rust toolchain to 2025-06-17 by @tautschnig in #4163 * Automatic cargo update to 2025-06-23 by @github-actions in #4172 * Stub panics during MIR transformation by @AlexanderPortland in #4169 * Bump tests/perf/s2n-quic from `b1b5bf8` to `32ba87d` by @dependabot in #4175 * Handle enums with zero or one variants by @zhassan-aws in #4171 * Introduce compiler timing script & CI job by @AlexanderPortland in #4154 * Upgrade Rust toolchain to 2025-06-18 by @tautschnig in #4166 * Cache dependencies for CI jobs by @AlexanderPortland in #4181 * Autoharness: Derive `Arbitrary` for structs and enums by @carolynzech in #4167 * Upgrade Rust toolchain to 2025-06-27 by @tautschnig in #4182 * Include wget in dependencies by @zhassan-aws in #4183 * Automatic cargo update to 2025-06-30 by @github-actions in #4186 * Add support for loop assigns in loop contracts by @thanhnguyen-aws in #4174 * Upgrade toolchain to 06/30 by @carolynzech in #4188 * Optimize reachability with non-mutating global passes by @AlexanderPortland in #4177 * Bump tests/perf/s2n-quic from `32ba87d` to `b8f8cca` by @dependabot in #4190 * Bump ncipollo/release-action from 1.16.0 to 1.18.0 by @dependabot in #4191 * Upgrade toolchain to 07/02 by @carolynzech in #4195 * Automatic Derivation Fixes by @carolynzech in #4194 **Full Changelog**: kani-0.63.0...kani-0.64.0 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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Context
When transforming MIR, we use both
TransformPass-es that operate over a single body andGlobalPass-es that require further context thus and operate over the whole program. Since these global passes could potentially modify the bodies they operate over, we currently re-run reachability after them to ensure that any changes are reflected in our reachability output.However, our global passes are largely gated behind unstable features (e.g.
-Z uninit-checksto check for uninitialized memory) or specific user actions (e.g. compiling w/RUSTFLAGS="--emit mir"), so this extra reachability collection is often done unnecessarily. Furthermore, some global passes (like emitting the generated MIR) do not modify the bodies they interact with at all, so re-doing collection is unneeded even when they are enabled.Changes
This PR modifies the
GlobalPasstrait to return a boolean representing if the pass modified the MIR in a way that could affect reachability. We then use the boolean flags for each result to redo reachability analysis only if aGlobalPasscould have affected its result.By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 and MIT licenses.