BE-512: HashQL: Allow cross-backend transitions for SwitchInt terminators

[indietyp]

🌟 What is the purpose of this PR?

SwitchInt terminators were previously blocked from generating cross-backend transitions during terminator placement, based on an assumption that coordinating branches across backends would be too complex. This restriction has been lifted, allowing SwitchInt to behave the same as Goto and permit cross-backend transitions. This enables more flexible execution placement for conditional branching logic.

🔍 What does this change?

• SwitchInt now calls add_goto_transitions instead of being a no-op, enabling cross-backend edge costs to be populated for blocks ending with a SwitchInt terminator.
• The test switchint_blocks_cross_backend has been renamed to switchint_allows_cross_backend and updated to assert that the Interpreter -> Embedding transition is now reachable with the expected cost.
• The switchint_edge_targets_are_branch_specific test has been updated to assert that cross-backend transitions are present rather than absent.
• The terminator placement snapshot has been updated to reflect the newly populated I->E and P->E transitions on edge[1].

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?

• Updated unit tests in terminator_placement/tests.rs covering SwitchInt cross-backend transition behaviour.
• Updated snapshot test reflecting the new edge cost matrix output.

❓ How to test this?

1. Run cargo test in libs/@local/hashql/mir.
2. Confirm all terminator placement tests pass, including the renamed switchint_allows_cross_backend test.

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Project	Deployment	Actions	Updated (UTC)
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[cursor]

PR Summary

Medium Risk
Changes execution-planning edge costs for all SwitchInt control flow; planners may choose different backend placements than before, though GraphRead and Postgres loop rules are unchanged.

Overview
SwitchInt terminator edges now use the same backend-transition rules as Goto, so terminator placement can assign cross-backend costs (e.g. Interpreter ↔ Embedding) on conditional branches, not only same-backend or fallback-to-Interpreter paths.

In add_terminator_specific_transitions, SwitchInt is merged with Goto and calls add_goto_transitions instead of leaving cross-backend pairs unset. Unit tests and the terminator-placement snapshot were updated to expect those transitions and costs on SwitchInt edges (including per-branch successor targets).

Note: The module-level transition table in mod.rs still describes the old SwitchInt rule; that comment was not updated in this diff.

^{Reviewed by Cursor Bugbot for commit 77c29af. Bugbot is set up for automated code reviews on this repo. Configure here.}

[indietyp]

• BE-537: Remove old filter API backend and wire up HashQL in the API #8827
• BE-513: HashQL: Rework dynamic aggregate size estimation #8697
• BE-512: HashQL: Allow cross-backend transitions for SwitchInt terminators #8696 👈 (View in Graphite)
• BE-524: HashQL: Remove island schedule module #8694
• BE-525: HashQL: Remove implicit type-widening from Integer operations, and make comparison size aware #8693
• BE-515: HashQL: Remove OFFSET 0 materialization fence from generated query #8650
• BE-514: HashQL: implement iterative adjustment passes in placement solver #8635
• BE-500, BE-501: HashQL: Unify mixed parameter resolution in data dependency analysis #8607
• BE-494: HashQL: Loop-breaker selection for recursive inlining #8600
• BE-482: HashQL: Remove logical not from MIR and fix postgres boolean lowering #8595
• BE-474: HashQL: Take into account terminator target eligibility in execution backend placement #8587
• BE-455: HashQL: Introduce evaluation orchestrator #8586
• BE-523: HashQL: Suspendable interpreter with structured values and input system #8675
• BE-522: HashQL: Expand stdlib type system with temporal types #8674
• BE-306: HashQL: PostgreSQL translation #8526
• BE-457: HashQL: MIR execution pipeline extensions for postgres compilation #8525
• BE-456: HashQL: Entity type model enrichment and graph store query extensions #8524
• BE-429: HashQL: Add island dependency graph with data requirement resolution #8501
• BE-428: HashQL: Simplify traversal tracking to path recording #8498
• BE-434: HashQL: Refactor entity storage path resolution with centralized schema mapping #8496
• BE-427: Add hashql-macros crate with procedural macros for ID types and symbols #8495
• main

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[augmentcode]

🤖 Augment PR Summary

Summary: Enables cross-backend transitions for blocks ending in SwitchInt terminators, aligning their behavior with Goto during terminator placement.
Changes: Updates the edge-cost matrix population logic and adjusts unit/snapshot tests to assert newly reachable cross-backend paths with expected costs.

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[augmentcode]

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 59.08%. Comparing base (02b718a) to head (77c29af).

Additional details and impacted files

@@                          Coverage Diff                           @@
##           bm/be-524-hashql-remove-island-dag    #8696      +/-   ##
======================================================================
- Coverage                               59.09%   59.08%   -0.02%     
======================================================================
  Files                                    1344     1343       -1     
  Lines                                  129787   129730      -57     
  Branches                                 5869     5866       -3     
======================================================================
- Hits                                    76704    76653      -51     
+ Misses                                  52180    52174       -6     
  Partials                                  903      903              

Flag	Coverage Δ
apps.hash-ai-worker-ts	1.41% <ø> (ø)
apps.hash-api	0.00% <ø> (ø)
local.hash-backend-utils	2.81% <ø> (ø)
local.hash-graph-sdk	9.63% <ø> (ø)
local.hash-isomorphic-utils	0.00% <ø> (ø)
rust.hash-graph-api	2.52% <ø> (ø)
rust.hashql-compiletest	28.26% <ø> (ø)
rust.hashql-eval	75.69% <ø> (ø)
rust.hashql-mir	86.94% <100.00%> (-0.01%)	⬇️

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[codspeed-hq]

Merging this PR will not alter performance

✅ 24 untouched benchmarks
⏩ 56 skipped benchmarks¹

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_{Comparing bm/be-512-hashql-switchint-allow-cross-backend-transitions (77c29af) with bm/be-524-hashql-remove-island-dag (30090d9)²}

Footnotes

1. 56 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-524-hashql-remove-island-dag (02b718a) during the generation of this report, so 0f66027 was used instead as the comparison base. There might be some changes unrelated to this pull request in this report. ↩