CI: compiler-output-regression red on main (h1_buffer_alias_negative native-region-proof workload)

[proggeramlug]

Summary

The compiler-output-regression gate is red on main. The native-region-proof harness reports one failed workload:

"failed_workloads": [ "h1_buffer_alias_negative" ]
##[error]Process completed with exit code 1.

All other workloads (loop_data_dependent, numeric_arrays, raw_numeric_object_fields, scalar_replacement_literals, …) pass.

Scope

Pre-existing on main, surfaced while landing #5016 (PR #5022); that PR is WASM-codegen only and does not touch native codegen, so it is not the cause. This is a native LLVM region/aliasing structural-contract regression in the h1_buffer_alias_negative fixture and needs someone with native-codegen context to bisect which recent change moved the structural report.

[proggeramlug]

Verified resolved on current main. Ran the exact CI invocation locally:

python3 scripts/compiler_output_regression.py suite --suite native-region-proof \
  --perry target/debug/perry --benchmark-mode smoke --runs 1 --perf-counters off --print-summary

Result: "failed_workloads": [] — h1_buffer_alias_negative is status: pass, exit_code: 0, as are all other workloads. The harness unit tests also pass (python3 -m unittest tests.test_compiler_output_regression → 40/40 OK).

The h1_buffer_alias_negative structural report has all 20 checks green, including the negative-proof aliasing contracts this issue is about:

• native_reps_no_unsafe_inbounds_claims: pass
• native_reps_no_unsafe_noalias_claims: pass
• native_reps_no_unchecked_unknown_bounds: pass
• native_reps_negative_denies_unsafe_noalias: pass

These are target-independent structural claims over the emitted LLVM IR (the fixture is a denial proof with min_vectorized_loops = 0), so the macOS-arm64 pass reflects the same region/aliasing analysis the Linux gate checks. The last red test.yml run on main was 2026-05-06 — stale; main has had many merges since (the structural regression appears to have been bisected out by intervening native-codegen work). Recommend a fresh CI run to confirm the gate is green on the Linux x86_64 runner; reopen if it reproduces there.

Verified on macOS arm64, current main (origin/main @ the latest merge).