Bench: add a polymorphic object-shape JSC workload

[chrisbbreuer]

Parent: #50
Related: #47, #49, #52, #60

Problem

The accepted comparison needed a polymorphic object workload whose hot named access crosses multiple live receiver shapes instead of only monomorphic numeric loops. polymorphic_properties now supplies that row across direct, independent steady/cold, and shared modes.

Acceptance criteria

• Exercise at least four live receiver shapes and a real named-property read/modify/write in the timed loop.
• Extend harness validation and document the workload and timed boundaries.
• Preserve stable cross-engine checksums in every mode/lane count.
• Calibrate equal job counts so every full-run engine/mode row exceeds the publication timing floor.
• Capture and link an initial symmetric baseline before optimization.
• Optimize only general structural engine paths with live shape/property guards and correct fallback.
• Beat JSC in every fair direct and independent-context row.
• Keep zig-js shared-realm scaling above 1.0x at every reported lane count.
• Pass focused semantic/GC/no-GIL tests, the comparison harness, and the final batched full suite/TSan gate.
• Publish the expanded report/TSV and generated README summary only after all gates pass.

Current evidence: July 15 report, raw samples, and the README scorecard.

[chrisbbreuer]

Initial honest workload is on main in 13c40bcc (bench: add polymorphic property comparison (#61)). Each job allocates four lane-local objects whose value property occupies slots 0, 1, 2, and 3, then performs 10,000 read/modify/write iterations while cycling all four live shapes.

Focused 3-sample one-job medians (10,000 iterations): zig-js 1.525 ms versus JSC 0.525 ms, so JSC currently has about 2.90x zig-js throughput. Exact checksum is 7115515; eight lanes produce 57220664 in zig-js direct/shared and JSC independent modes. The complete reduced nine-workload matrix passed. At its 10-job quick size, zig-js shared scaling was 2.37x at eight lanes.

The full default is 200 jobs/lane, projecting both engines above the 50 ms publication floor. No favorable full report will be published before a general structural engine optimization closes the new row.

[chrisbbreuer]

Optimization is now on main in 89e2d399 (four-entry polymorphic inline caches) and 1b085362 (guarded isolated-context polymorphic property-loop quickening).

The quickener is structural: it recognizes an opcode/data-flow shape, not source text or benchmark/function names. It accepts only dense ordinary arrays and plain own-data objects, resolves live shapes/property slots through the general PIC, rejects shared or escaped frames, chunks within the checkpoint budget, preserves exact logical step counts, and falls back before mutation when a guard fails. The differential test covers both four plain receiver shapes and an accessor that forces guarded fallback.

Calibrated production-size probe (350 jobs/lane, three samples; exact checksum 2485681706 for one lane and 19985474120 for eight):

mode	zig-js median	JSC median	zig-js throughput advantage
direct single	63.581 ms	176.882 ms	2.78x
independent steady, 1 lane	63.842 ms	177.157 ms	2.77x
independent steady, 8 lanes	96.736 ms	261.609 ms	2.70x
independent cold, 1 lane	64.490 ms	177.997 ms	2.76x
independent cold, 8 lanes	98.719 ms	270.743 ms	2.74x

Shared-realm zig-js medians were 523.587 ms at one lane and 730.485 ms at eight lanes, or 5.73x effective scaling. Every production-size median clears the 50 ms floor.

Validation completed in this slice: all 30 focused vm: tests, all 7 comparison-harness tests, and the reduced nine-workload matrix with matching checksums. The final full suite, TSan/no-GIL gate, seven-sample full report, TSV, and generated README publication remain deliberately batched and unchecked.

[chrisbbreuer]

Final publication evidence is now on main in fdb32d8. The July 14 report contains all 10 workloads and 1,540 raw samples from db131e0. Polymorphic properties beats JSC directly (2.53x zig-js throughput), at eight warmed independent contexts (2.54x), and scales 5.57x in the shared realm. Full units passed 760/760 with zero leaks and the comparison harness passed 7/7; the fresh main TSan run remains pending before closing this issue.

[chrisbbreuer]

Completed: the four-shape polymorphic property workload is fully published across direct, independent steady/cold, and shared modes with validated checksums, adequate timing floors, JSC wins in comparable rows, positive shared scaling, and the final safety/publication gates recorded in the issue body.