[AIROCMLIR-602] Add MHAL dialect lit coverage

[bogdan-petkovic]

Motivation

The MHAL dialect (vendored under external/mlir-hal/) currently has very thin lit coverage, roughly 32% of its source lines are exercised, and one of its conversion passes (--convert-mhal-to-gpu) was not even reachable from rocmlir-opt because its tablegen-generated registration function was never called. This PR closes both gaps:

1. Wires registerMHALConversionPasses() into rocMLIR's CLI-pass registration entry point, so --convert-mhal-to-gpu is now discoverable from rocmlir-opt --help and can be driven by lit tests.

2. Adds eight new lit tests under mlir/test/Dialect/MHAL/ that systematically exercise every MHAL transform pass, the MHAL→GPU conversion pass, and all three custom MHAL attributes (round-trip).

The goal is to catch regressions in MHAL parsing/printing and in the pass pipeline at lit time, instead of requiring a full host+device E2E build, and to make any future refactor in external/mlir-hal/lib/Dialect/MHAL/Transforms/ and lib/Conversion/MHALToGPU/ immediately observable.

Technical Details

Source change — mlir/include/mlir/InitRocMLIRPasses.h (+5 lines)
MHAL declares its passes in two separate tablegen groups: Dialect/MHAL/Transforms/Passes.td (registered via registerMHALPasses() in vendored InitMHALPasses.h) and Conversion/MHALPasses.td with -name MHALConversion (registered via the generated registerMHALConversionPasses()). The conversion group was implemented but never wired into any registration entry point, so --convert-mhal-to-gpu was unreachable from rocmlir-opt. This PR adds the missing registerMHALConversionPasses() call inside registerRocMLIRPasses(), with an inline comment explaining the asymmetric tablegen grouping.

The fix is intentionally in rocMLIR-owned code (not in external/mlir-hal/) so the whole patch stays under a single AIROCMLIR-602 commit and adds no merge surface to the in-flight MHAL decoupling work (#2333, #2325).

Tests — 8 new files under mlir/test/Dialect/MHAL/ (+~1000 lines)
attrs-roundtrip.mlir — Custom parse/print for #mhal.target_obj, #mhal.kernel_pkg, #mhal.prefill. Pretty- and generic-printer round-trip; all TargetObjectType and TargetType keywords.

bufferize.mlir — --mhal-bufferize post-#2333 no-op path; preserves MHAL arg attrs and mhal.targets.

convert-mhal-to-gpu.mlir — --convert-mhal-to-gpu: alloc / memcpy / launch / wait; write_access copy-back; GPU-over-CPU selection; explicit negative checks for no-targets and CPU-only callees; scalar operand path.

drop-metadata.mlir — --mhal-drop-binary-metadata: strips properties/kernels; fat-binary across two arches; idempotence; top-level-only isolation.

package-targets.mlir — --mhal-package-targets: single-arch and multi-arch (CHECK-DAG); multiple binaries per kernel module; unmarked nested module and dangling original_func skipped.

prefill.mlir — --mhal-prefill: one/many prefills; f16/i8/i32 element-type matching with non-zero argIdx; missing properties key/dict; mixed-attr dyn_cast filter.

select-targets.mlir — --mhal-select-targets happy paths (4 RUN configurations): arch filter, type filter, last-match-wins, empty target-types wildcard, triple-vs-chip-only SystemDevice::isCompatible.

select-targets-error.mlir — --mhal-select-targets error path with --verify-diagnostics: CPU-only-with-GPU-required, GPU-arch-mismatch, multi-non-matching-packages.

Each test file's leading // COM: comments cite the exact external/mlir-hal/lib/... source file (and line numbers, where relevant) being exercised.

Test Plan

PR CI

Test Result

• PR CI

Submission Checklist

• Look over the contributing guidelines at https://github.com/ROCm/ROCm/blob/develop/CONTRIBUTING.md#pull-requests.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #2394      +/-   ##
===========================================
+ Coverage    79.50%   82.40%   +2.89%     
===========================================
  Files          100      120      +20     
  Lines        31016    42830   +11814     
  Branches      4819     7112    +2293     
===========================================
+ Hits         24659    35291   +10632     
- Misses        4245     4881     +636     
- Partials      2112     2658     +546     

Flag	Coverage Δ
gfx950	82.28% <100.00%> (?)
mfma	82.27% <100.00%> (+2.77%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
mlir/include/mlir/InitRocMLIRPasses.h	100.00% <100.00%> (ø)

... and 122 files with indirect coverage changes

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