Add mcTVM mctvm mxcc perf regression gate

[ghangz]

Summary

• Adds a focused mctvm mxcc perf regression gate improvement for MetaX-MACA/mcTVM.
• The change targets MetaX MACA development and validation workflows, with emphasis on earlier diagnostics, reproducible logs, or safer benchmark tooling.
• Existing default behavior is kept compatible; the new logic is scoped to explicit checks, helper tools, or validation metadata.

Validation

• Verified on Gitee.AI MetaX GPU resources: mctvm_TileLang_20260701, 6/6 PASS.
• Branch validation command: python tools/mxcc_perf_gate.py --self-test x y
• Pull request text is intentionally ASCII-only to avoid encoding issues on web forms and API clients.

Review notes

• Source branch: ghangz:mengz/mctvm-mxcc-perf-regression-gate
• Target branch: MetaX-MACA/mcTVM:dev
• Maintainers can modify this branch if follow-up adjustments are needed.

[gemini-code-assist]

Code Review

This pull request introduces a new performance gating script, tools/mxcc_perf_gate.py, designed to compare baseline and current compilation times and fail if regressions are detected. Feedback points out a critical bug in the regression detection logic: the script currently flags performance improvements as regressions (when ratio < -TOLERANCE) instead of flagging actual compile-time increases (when ratio > TOLERANCE).

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[gemini-code-assist]

The metric being measured is compile_seconds. An increase in compile time (where new > old and ratio > 0) represents a performance regression. However, the current logic flags a regression when ratio < -TOLERANCE (which is actually a performance improvement) and treats any increase in compile time as acceptable. This should be inverted so that a regression is triggered when ratio > TOLERANCE.

Suggested change

	status = "regression" if ratio < -TOLERANCE else "ok"
	status = "regression" if ratio > TOLERANCE else "ok"