BE-304: HashQL: Terminator placement based on capabilities

[indietyp]

🌟 What is the purpose of this PR?

Adds terminator placement analysis to the MIR execution planning pipeline. This complements statement placement by analyzing control flow edges rather than individual statements, determining which backend transitions are valid at each edge and their associated transfer costs.

🔍 What does this change?

• Introduces TransMatrix for encoding valid (source → destination) backend transitions per edge
• Adds TerminatorCostVec to collect transition matrices for all edges in a body
• Implements TerminatorPlacement analysis that computes costs based on:
  • Liveness analysis (which locals cross edges)
  • SCC detection (loop membership for Postgres restrictions)
  • Terminator-specific rules (GraphRead, SwitchInt, Goto)
• Moves execution/ module from pass/analysis/ to pass/ (organizational)
• Adds helper methods to BodyFootprint for computing average transfer costs

Pre-Merge Checklist 🚀

🚢 Has this modified a publishable library?

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

📜 Does this require a change to the docs?

• are internal and do not require a docs change

🕸️ Does this require a change to the Turbo Graph?

• do not affect the execution graph

🛡 What tests cover this?

New unit tests in terminator_placement/tests.rs covering loops, self-loops, SwitchInt, GraphRead, and Postgres restrictions
Snapshot test for terminator placement output

❓ How to test this?

cargo nextest run --package hashql-mir terminator_placement

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[cursor]

PR Summary

Medium Risk
Introduces new control-flow transition/cost logic (loop/SCC and liveness-driven) that will affect execution planning decisions; while well-tested, incorrect cost/transition constraints could lead to suboptimal or invalid backend switching.

Overview
Adds a new MIR terminator placement analysis that computes per-control-flow-edge backend transition legality and costs, using liveness + SCC/loop detection and terminator-specific rules (Goto, SwitchInt, GraphRead) to constrain transitions (including stricter Postgres restrictions) and derive transfer costs from size estimates.

Refactors execution-related code out of pass::analysis into a new top-level pass::execution module, updates imports/call sites, and extends size-estimation utilities (Estimate::eval, Footprint::average, range/unit helpers) plus Cost helpers (MAX, saturating_add, TargetId::abbreviation) to support overflow-safe transfer-cost calculation. Also adds list support to the MIR rvalue builder macro and introduces comprehensive unit/snapshot tests for terminator placement.

^{Written by Cursor Bugbot for commit 9a0ea84. 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
• BE-304: HashQL: Terminator placement based on capabilities #8359 👈 (View in Graphite)
• 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

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[codecov]

Codecov Report

❌ Patch coverage is 95.30387% with 34 lines in your changes missing coverage. Please review.
✅ Project coverage is 84.09%. Comparing base (cf5e803) to head (9a0ea84).

Files with missing lines	Patch %	Lines
...mir/src/pass/execution/terminator_placement/mod.rs	94.00%	13 Missing and 2 partials ⚠️
.../mir/src/pass/analysis/size_estimation/estimate.rs	47.05%	9 Missing ⚠️
...hql/mir/src/pass/analysis/size_estimation/range.rs	75.00%	4 Missing ⚠️
...r/src/pass/execution/terminator_placement/tests.rs	99.24%	2 Missing and 1 partial ⚠️
...mir/src/pass/analysis/size_estimation/footprint.rs	88.23%	1 Missing and 1 partial ⚠️
...shql/mir/src/pass/analysis/size_estimation/unit.rs	91.66%	1 Missing ⚠️

Additional details and impacted files

@@                                          Coverage Diff                                           @@
##           bm/be-303-hashql-split-basic-blocks-depending-on-largest-available    #8359      +/-   ##
======================================================================================================
+ Coverage                                                               83.87%   84.09%   +0.22%     
======================================================================================================
  Files                                                                     344      346       +2     
  Lines                                                                   50913    51637     +724     
  Branches                                                                 1308     1319      +11     
======================================================================================================
+ Hits                                                                    42701    43423     +722     
+ Misses                                                                   7746     7744       -2     
- Partials                                                                  466      470       +4     

Flag	Coverage Δ
rust.hashql-compiletest	29.69% <ø> (ø)
rust.hashql-mir	90.79% <95.30%> (+0.36%)	⬆️

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[augmentcode]

🤖 Augment PR Summary

Summary: Adds terminator-edge backend transition planning to the HashQL MIR execution planner.
Why: Complements statement placement by deciding where backend switches are valid and how costly they are.
Key changes:

• New TransMatrix + TerminatorCostVec to store (source→dest) transition validity/cost per terminator edge.
• New TerminatorPlacement analysis combining liveness, SCC/loop detection, and size-estimation to compute transfer costs and enforce backend rules (GraphRead/SwitchInt/Goto, Postgres restrictions).
• Execution modules reorganized from pass/analysis/execution to pass/execution and exports updated.
• Size-estimation extended with Estimate::eval, Footprint::average, and range/unit helpers used for transfer-cost calculations.
• Cost enhanced with MAX sentinel and saturating_add to avoid overflow while accumulating costs.
• MIR builder rvalue! gains list support, enabling tests to construct list values.
• New unit + snapshot tests covering loops/self-loops, SwitchInt, GraphRead, and unbounded transfer costs.

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[augmentcode]

Review completed. 1 suggestions posted.

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

[codspeed-hq]

Merging this PR will not alter performance

✅ 21 untouched benchmarks
⏩ 20 skipped benchmarks¹

---

_{Comparing bm/be-304-hashql-terminator-coloring-based-on-capabilities (9a0ea84) with bm/be-303-hashql-split-basic-blocks-depending-on-largest-available (cf5e803)}

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. ↩

Your organization requires reapproval when changes are made, so Graphite has dismissed approvals. See the output of git range-diff at https://github.com/hashintel/hash/actions/runs/21756355054