BE-264: HashQL: Rename SROA to ForwardSubstitution for better semantic clarity

[indietyp]

🌟 What is the purpose of this PR?

Rename the SROA (Scalar Replacement of Aggregates) transformation pass to ForwardSubstitution to better reflect its actual functionality. This pass resolves place operands to their ultimate sources by tracing data dependencies through assignments, projections, and block parameters.

🔍 What does this change?

• Renames Sroa class to ForwardSubstitution across the codebase
• Updates documentation to clarify that this pass performs forward substitution of values through data dependencies
• Renames the test suite from mir/pass/transform/sroa to mir/pass/transform/forward-substitution
• Renames cp module to copy_propagation for consistency and clarity
• Updates benchmarks to use the new class name
• Improves documentation to better explain the differences between CopyPropagation and ForwardSubstitution

🛡 What tests cover this?

Existing tests have been preserved and renamed to match the new terminology.

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

[cursor]

PR Summary

• Replace Sroa with ForwardSubstitution across MIR passes, compiletest suites, pipelines, and benches; update suite registration and UI test paths/labels
• Update docs/comments to describe forward substitution semantics and its interaction with other passes; adjust callgraph and InstSimplify references
• Rename transform::cp to transform::copy_propagation; update imports/usages (e.g., propagate_block_params) and add/adjust tests under copy_propagation
• Add new mir/pass/transform/forward-substitution suite and benchmarks; remove/rename the old SROA suite/assets

^{Written by Cursor Bugbot for commit 5f7b4cc. This will update automatically on new commits. Configure here.}

[indietyp]

• 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 👈 (View in Graphite)
• 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

✅ All modified and coverable lines are covered by tests.
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Additional details and impacted files

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Flag	Coverage Δ
rust.hashql-compiletest	46.65% <ø> (?)
rust.hashql-mir	87.22% <100.00%> (?)

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[augmentcode]

🤖 Augment PR Summary

Summary: Renames the MIR transform pass formerly called SROA to ForwardSubstitution to better match what the pass actually does (resolving place operands to their ultimate sources via data-dependency tracing).

Changes:

• Rename pass implementation and public exports (Sroa �e2 ForwardSubstitution) and update module wiring in hashql_mir::pass::transform.
• Expand/adjust docs to describe forward substitution behavior and how it combines with DSE to enable SROA-like aggregate decomposition.
• Rename cp module to copy_propagation and update internal imports (e.g., propagate_block_params) accordingly.
• Update compiletest suites: add/rename suite to mir/pass/transform/forward-substitution and run it in the MIR pipeline before InstSimplify.
• Update MIR benchmarks to use ForwardSubstitution and rename benchmark group from sroa to forward_substitution.
• Migrate/rename UI tests and snapshots from sroa/cp directories to forward_substitution/copy_propagation.

Technical Notes: This is primarily a semantic rename and documentation clarification; functional behavior should remain the same, with ForwardSubstitution positioned as the more comprehensive propagation pass vs CopyPropagation.

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[augmentcode]

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[codspeed-hq]

CodSpeed Performance Report

Merging this PR will degrade performance by 12.55%

_{Comparing bm/be-264-hashql-rename-sroa-to-projectionforwarding (5f7b4cc) with main (d451c18)}

Summary

❌ 1 (👁 1) regressed benchmark
✅ 13 untouched benchmarks
🆕 3 new benchmarks

Performance Changes

	Benchmark	BASE	HEAD	Efficiency
👁	diamond	6.5 µs	7.5 µs	-12.55%
🆕	diamond	N/A	16.9 µs	N/A
🆕	complex	N/A	22.6 µs	N/A
🆕	linear	N/A	8.1 µs	N/A