BE-372: HashQL: Add traversal-aware liveness analysis for optimizing entity projections

[indietyp]

🌟 What is the purpose of this PR?

This PR adds a traversal-aware liveness analysis that suppresses uses of traversal source locals when assigning to known traversal destinations. This allows dead code elimination to remove source locals when all their uses are through extracted traversals.

🔍 What does this change?

• Adds TraversalLivenessAnalysis that extends standard liveness analysis with special handling for traversal extraction
• When a traversal destination is fully defined, uses of the traversal source on the right-hand side are not marked as live
• Updates TerminatorPlacement to use the traversal-aware liveness analysis
• Adds comprehensive tests for the new analysis
• Exposes helper methods on Traversals to check if a local is a traversal destination

Pre-Merge Checklist 🚀

🚢 Has this modified a publishable library?

This PR:

• does not modify any publishable blocks or libraries, or modifications do not need publishing

📜 Does this require a change to the docs?

The changes in this PR:

• are internal and do not require a docs change

🕸️ Does this require a change to the Turbo Graph?

The changes in this PR:

• do not affect the execution graph

🛡 What tests cover this?

• Added unit tests for TraversalLivenessAnalysis covering various scenarios
• Updated TerminatorPlacement tests to use the new analysis

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Project	Deployment	Actions	Updated (UTC)
hash	Ready	Preview, Comment	Feb 6, 2026 3:46pm

3 Skipped Deployments

Project	Deployment	Actions	Updated (UTC)
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hashdotdesign-tokens	Ignored	Preview	Feb 6, 2026 3:46pm
petrinaut	Skipped		Feb 6, 2026 3:46pm

[cursor]

PR Summary

Medium Risk
Changes core dataflow results used for execution planning costs; incorrect skip conditions could under-approximate liveness and lead to invalid backend transition decisions, though behavior is guarded by targeted tests.

Overview
Adds TraversalLivenessAnalysis, a new liveness dataflow variant that suppresses marking the traversal source local as live when fully assigning to a known traversal destination, enabling later passes (e.g., DCE) to drop the source when only projections are used.

Wires this traversal-aware liveness into TerminatorPlacement by requiring a Traversals input and using it when computing live-in sets, which can reduce computed cross-backend transfer costs; updates exports, extends Traversals with contains()/source() helpers (and makes insert available within the crate), and adds snapshot/unit tests covering the new liveness semantics and a transfer-cost regression case.

^{Written by Cursor Bugbot for commit 61a2ae7. This will update automatically on new commits. Configure here.}

[indietyp]

Warning

This pull request is not mergeable via GitHub because a downstack PR is open. Once all requirements are satisfied, merge this PR as a stack on Graphite.
Learn more

• BE-372: HashQL: Add traversal-aware liveness analysis for optimizing entity projections #8363 👈 (View in Graphite)
• BE-304: HashQL: Terminator placement based on capabilities #8359
• BE-303: HashQL: Split MIR basic blocks by target support #8354
• BE-364: Rework symbol representation for speed and size #8343
• BE-360: HashQL: Rework compiletest UI #8340
• BE-302: HashQL: Statement cost analysis for execution target placement #8339
• BE-317: HashQL: Implement TraversalExtraction pass #8331
• BE-315: HashQL: Add GraphReadFilter source variant to MIR #8323
• BE-301: HashQL: Implement size estimation analysis for MIR #8278
• BE-273: HashQL: Profile and benchmark MIR interpreter #8251
• BE-272: HashQL: Add numeric addition and subtraction operators to MIR #8250
• BE-257: HashQL: Implement MIR interpreter with runtime value representation #8245
• BE-271: HashQL: Implement PostInline pass #8240
• BE-269: HashQL: Move PreInline out into Canonicalization pass #8239
• BE-268: HashQL: Rename PreInlining to PreInline for consistency #8238
• BE-270: HashQL: Optimize empty tuples to unit constants in MIR #8237
• BE-197: Implement MIR inline pass for HashQL #8236
• BE-267: Use bump scopes instead of full resets across transformation passes #8234
• BE-266: HashQL: Implement PreInlining pass for MIR optimization #8233
• BE-265: HashQL: Make CopyPropagation aware of local re-assignments #8231
• BE-264: HashQL: Rename SROA to ForwardSubstitution for better semantic clarity #8230
• BE-263: HashQL: add body! macro for declarative MIR construction in tests #8229
• BE-261: HashQL: Implement Administrative Reduction pass for MIR #8227
• BE-262: HashQL: Do not intern empty slices #8223
• BE-260: HashQL: Switch to bump allocator with scoping support #8218
• BE-259: HashQL: Add benchmarks for type system operations #8216
• BE-227: HashQL: Implement call graph analysis for MIR #8214
• BE-258: HashQL: Add Changed enum to track MIR transformation pass modifications #8210
• BE-255: HashQL: Implement Copy Propagation (CP) pass for MIR #8207
• BE-231: HashQL: Add InstSimplify pass for MIR instruction simplification and constant folding #8206
• BE-254: Add CodSpeed benchmarking for HashQL MIR transformation passes #8204
• main

This stack of pull requests is managed by Graphite. Learn more about stacking.

[codspeed-hq]

Merging this PR will not alter performance

✅ 21 untouched benchmarks
⏩ 20 skipped benchmarks¹

---

_{Comparing bm/be-372-hashql-do-not-consider-traversals-during-liveness-analysis (61a2ae7) with bm/be-304-hashql-terminator-coloring-based-on-capabilities (4298d22)²}

Footnotes

1. 20 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

2. No successful run was found on bm/be-304-hashql-terminator-coloring-based-on-capabilities (9a0ea84) during the generation of this report, so 367b8a2 was used instead as the comparison base. There might be some changes unrelated to this pull request in this report. ↩

[augmentcode]

🤖 Augment PR Summary

Summary: This PR adds traversal-aware liveness analysis to better optimize and cost entity projection traversals in HashQL MIR.

Changes:

• Introduce TraversalLivenessAnalysis that can suppress liveness gens for a traversal source local when defining a registered traversal destination.
• Export the new analysis alongside standard LivenessAnalysis.
• Extend Traversals with contains() and source(), and widen insert visibility for intra-crate use.
• Update TerminatorPlacement to run traversal-aware liveness and accept a Traversals input.
• Add new liveness unit tests + insta snapshots, and a terminator-placement regression test showing reduced transfer cost when traversals are present.

Technical Notes: The skip behavior only triggers for Assign statements whose LHS is an unprojected traversal destination local (full definition).

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[augmentcode]

Review completed. 2 suggestions posted.

Comment augment review to trigger a new review at any time.

[codecov]

Codecov Report

❌ Patch coverage is 98.61111% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 84.15%. Comparing base (9a0ea84) to head (61a2ae7).

Files with missing lines	Patch %	Lines
...hql/mir/src/pass/analysis/dataflow/liveness/mod.rs	93.18%	1 Missing and 2 partials ⚠️

Additional details and impacted files

@@                                      Coverage Diff                                       @@
##           bm/be-304-hashql-terminator-coloring-based-on-capabilities    #8363      +/-   ##
==============================================================================================
+ Coverage                                                       84.09%   84.15%   +0.05%     
==============================================================================================
  Files                                                             346      346              
  Lines                                                           51637    51845     +208     
  Branches                                                         1319     1324       +5     
==============================================================================================
+ Hits                                                            43423    43629     +206     
  Misses                                                           7744     7744              
- Partials                                                          470      472       +2     

Flag	Coverage Δ
rust.hashql-compiletest	29.69% <ø> (ø)
rust.hashql-mir	90.88% <98.61%> (+0.09%)	⬆️

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