Refactor simd_bitmask to reduce the number of iterations #4129
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tautschnig
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Jun 4, 2025
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This PR is co-authored with @tautschnig. Background: In #4127 we enabled certain target features that are platform dependent (e.g. `sse` and `sse2` for x86_64 and `neon` for aarch64) which resulted in using the `simd_bitmask` intrinsic more frequently. Kani's current model of that intrinsic (https://github.com/model-checking/kani/blob/5f14b735b74f3ae3f9f1c64ce5656e1e735d42ea/library/kani/src/models/mod.rs#L72) uses a loop that iterates `LANE` times, which requires harnesses that touch this code (e.g. that use the `HashSet` data structure) to have a large unwinding value, which results in a significant slowdown. This PR refactors this function through rewriting it using a nested loop and manually unwinding the inner loop (which operates over the bits in a byte) so that a large unwinding value is not needed. 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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These are the automatically-generated release notes: ``` ## What's Changed * Toolchain upgrade to nightly-2025-05-04 by @thanhnguyen-aws in #4059 * Automatic toolchain upgrade to nightly-2025-05-05 by @github-actions in #4060 * Automatic toolchain upgrade to nightly-2025-05-06 by @github-actions in #4061 * Enable target features: x87 and sse2 by @thanhnguyen-aws in #4062 * Fix the bug: Loop contracts are not composable with function contracts by @thanhnguyen-aws in #3979 * Automatic cargo update to 2025-05-12 by @github-actions in #4066 * Bump tests/perf/s2n-quic from `6aa9975` to `5f323b7` by @dependabot in #4068 * Fix stabilization instructions in RFC intro by @carolynzech in #4067 * Add support for quantifiers by @qinheping in #3993 * Toolchain upgrade to nightly-2025-05-07 by @thanhnguyen-aws in #4070 * Automatic toolchain upgrade to nightly-2025-05-08 by @github-actions in #4071 * Automatic toolchain upgrade to nightly-2025-05-09 by @github-actions in #4072 * Automatic toolchain upgrade to nightly-2025-05-10 by @github-actions in #4073 * Clippy/Stylistic Fixes by @carolynzech in #4074 * Upgrade toolchain to 2025-05-14 by @zhassan-aws in #4076 * Autoharness argument validation: only error on `--quiet` if `--list` was passed by @carolynzech in #4069 * Upgrade Rust toolchain to 2025-05-16 by @zhassan-aws in #4080 * Automatic toolchain upgrade to nightly-2025-05-17 by @github-actions in #4081 * Add setup scripts for Ubuntu 20.04 by @zhassan-aws in #4082 * Automatic toolchain upgrade to nightly-2025-05-18 by @github-actions in #4083 * Automatic cargo update to 2025-05-19 by @github-actions in #4086 * Automatic toolchain upgrade to nightly-2025-05-19 by @github-actions in #4085 * Automatic toolchain upgrade to nightly-2025-05-20 by @github-actions in #4091 * Bump tests/perf/s2n-quic from `5f323b7` to `22434aa` by @dependabot in #4089 * Fix the error that Kani panics when there is no external parameter in quantifier's closure. by @thanhnguyen-aws in #4088 * Update toolchain to 2025-05-22 by @carolynzech in #4098 * Use our toolchain when invoking `cargo metadata` by @carolynzech in #4090 * Automatic toolchain upgrade to nightly-2025-05-23 by @github-actions in #4099 * Automatic toolchain upgrade to nightly-2025-05-24 by @github-actions in #4101 * Automatic toolchain upgrade to nightly-2025-05-25 by @github-actions in #4102 * Fix a bug codegening `SwitchInt`s with only an otherwise branch by @bkirwi in #4095 * Automatic toolchain upgrade to nightly-2025-05-26 by @github-actions in #4104 * Automatic cargo update to 2025-05-26 by @github-actions in #4105 * Bump tests/perf/s2n-quic from `22434aa` to `550afb3` by @dependabot in #4106 * Automatic toolchain upgrade to nightly-2025-05-27 by @github-actions in #4107 * Update `kani::mem` pointer validity documentation by @carolynzech in #4092 * Add support for edition 2018 crates using assert! (Fixes #3717) by @sintemal in #4096 * Automatic toolchain upgrade to nightly-2025-05-28 by @github-actions in #4113 * Automatic toolchain upgrade to nightly-2025-05-29 by @github-actions in #4115 * Automatic toolchain upgrade to nightly-2025-05-30 by @github-actions in #4118 * Handle generic defaults in BoundedArbitrary derives by @zhassan-aws in #4117 * Automatic cargo update to 2025-06-02 by @github-actions in #4121 * Bump tests/perf/s2n-quic from `550afb3` to `8f54b57` by @dependabot in #4122 * Upgrade Rust toolchain to 2025-06-02 by @zhassan-aws in #4123 * Automatic toolchain upgrade to nightly-2025-06-03 by @github-actions in #4125 * Finish deprecating `--enable-unstable`, `--restrict-vtable`, and `--write-json-symtab` by @carolynzech in #4110 * `ty_mangled_name`: only use non-mangled name if `-Zcffi` is enabled. by @carolynzech in #4114 * Improve Help Menu by @carolynzech in #4109 * Start stabilizing `--jobs` and `list`; deprecate default memory checks by @carolynzech in #4108 * Refactor simd_bitmask to reduce the number of iterations by @zhassan-aws in #4129 * Set target features depending on the target architecture by @zhassan-aws in #4127 * Bump some versions suggested by cargo-outdated by @zhassan-aws in #4131 * Improve linking error output for `#[no_std]` crates by @AlexanderPortland in #4126 * Fix the git log command in the toolchain update script by @zhassan-aws in #4139 * Gate quantifiers behind an experimental feature by @thanhnguyen-aws in #4141 * Automatic cargo update to 2025-06-09 by @github-actions in #4145 ## New Contributors * @bkirwi made their first contribution in #4095 * @sintemal made their first contribution in #4096 * @AlexanderPortland made their first contribution in #4126 **Full Changelog**: kani-0.62.0...kani-0.63.0 ``` By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 and MIT licenses. --------- Co-authored-by: Carolyn Zech <carolynzech@gmail.com>
zhassan-aws
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This PR is co-authored with @tautschnig. Background: In #4127 we enabled certain target features that are platform dependent (e.g. `sse` and `sse2` for x86_64 and `neon` for aarch64) which resulted in using the `simd_bitmask` intrinsic more frequently. Kani's current model of that intrinsic (https://github.com/model-checking/kani/blob/5f14b735b74f3ae3f9f1c64ce5656e1e735d42ea/library/kani/src/models/mod.rs#L72) uses a loop that iterates `LANE` times, which requires harnesses that touch this code (e.g. that use the `HashSet` data structure) to have a large unwinding value, which results in a significant slowdown. This PR refactors this function through rewriting it using a nested loop and manually unwinding the inner loop (which operates over the bits in a byte) so that a large unwinding value is not needed. 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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This PR is co-authored with @tautschnig.
Background: In #4127 we enabled certain target features that are platform dependent (e.g.
sseandsse2for x86_64 andneonfor aarch64) which resulted in using thesimd_bitmaskintrinsic more frequently. Kani's current model of that intrinsic (kani/library/kani/src/models/mod.rs
Line 72 in 5f14b73
LANEtimes, which requires harnesses that touch this code (e.g. that use theHashSetdata structure) to have a large unwinding value, which results in a significant slowdown.This PR refactors this function through rewriting it using a nested loop and manually unwinding the inner loop (which operates over the bits in a byte) so that a large unwinding value is not needed.
By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 and MIT licenses.