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BE-512: HashQL: Allow cross-backend transitions for SwitchInt terminators#8696

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BE-512: HashQL: Allow cross-backend transitions for SwitchInt terminators#8696
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bm/be-512-hashql-switchint-allow-cross-backend-transitions

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@indietyp indietyp commented May 4, 2026

🌟 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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cursor Bot commented May 4, 2026 •
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PR Summary

Medium Risk
Changes execution-planning cost matrices for conditional branches, which can shift backend placement decisions though Postgres/loop/GraphRead rules are unchanged.

Overview
Terminator placement now treats SwitchInt edges like Goto: add_terminator_specific_transitions routes both through add_goto_transitions, so cross-backend transitions (e.g. Interpreter ↔ Embedding) get transfer plus switch costs instead of being omitted.

Tests and the terminator placement snapshot were updated to expect those edges on SwitchInt branches (including per-branch successor targets).

Reviewed by Cursor Bugbot for commit 7323f1e. Bugbot is set up for automated code reviews on this repo. Configure here.

@github-actions github-actions Bot added area/libs Relates to first-party libraries/crates/packages (area) type/eng > backend Owned by the @backend team area/tests New or updated tests labels May 4, 2026
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indietyp commented May 4, 2026 •
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@indietyp indietyp mentioned this pull request May 4, 2026
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augmentcode Bot commented May 4, 2026

🤖 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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codecov Bot commented May 4, 2026 •
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Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 59.10%. Comparing base (3dfb99e) to head (7323f1e).

Additional details and impacted files 
@@                          Coverage Diff                           @@
##           bm/be-524-hashql-remove-island-dag    #8696      +/-   ##
======================================================================
- Coverage                               59.11%   59.10%   -0.01%     
======================================================================
  Files                                    1341     1341              
  Lines                                  129570   129566       -4     
  Branches                                 5849     5849              
======================================================================
- Hits                                    76589    76585       -4     
  Misses                                  52078    52078              
  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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@indietyp indietyp force-pushed the bm/be-524-hashql-remove-island-dag branch from 11715f8 to bb97a73 Compare May 20, 2026 14:46
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@indietyp indietyp force-pushed the bm/be-524-hashql-remove-island-dag branch from bb97a73 to 7c2c99f Compare May 22, 2026 11:21
@indietyp indietyp force-pushed the bm/be-512-hashql-switchint-allow-cross-backend-transitions branch from 026ce7b to b7cf577 Compare May 22, 2026 11:21
@indietyp indietyp force-pushed the bm/be-524-hashql-remove-island-dag branch from 7c2c99f to fed3275 Compare May 25, 2026 13:27
@indietyp indietyp force-pushed the bm/be-512-hashql-switchint-allow-cross-backend-transitions branch from b7cf577 to db1e44d Compare May 25, 2026 13:27
@indietyp indietyp force-pushed the bm/be-524-hashql-remove-island-dag branch from fed3275 to 2ffc3ed Compare May 25, 2026 13:58
@indietyp indietyp force-pushed the bm/be-512-hashql-switchint-allow-cross-backend-transitions branch from db1e44d to 0a4f75a Compare May 25, 2026 13:58
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@indietyp indietyp force-pushed the bm/be-524-hashql-remove-island-dag branch from 2fc2314 to c62ac8e Compare May 27, 2026 07:11
@indietyp indietyp force-pushed the bm/be-512-hashql-switchint-allow-cross-backend-transitions branch from c883c9e to 7323f1e Compare May 28, 2026 13:27
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