[Enhancement](compile) Specific x86-64-v3 arch when AVX2 enabled

[zclllyybb]

AVX2 is only a part of x86-64-v3. when avx2 supported, it can be basically determined that x86-64-v3 is also supported. Enabling it introduces some performance benefits.

[Thearas]

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[zclllyybb]

/review

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[Copilot]

Pull request overview

Updates backend build flags so that when USE_AVX2 is enabled, compilation targets the x86-64-v3 micro-architecture level for potential performance gains.

Changes:

• Add -march=x86-64-v3 to BE compile options when USE_AVX2 is enabled.

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[github-actions]

Summary

This change is not safe to merge as-is. -march=x86-64-v3 is broader than -mavx2, but Doris' runtime/build/release contract still models this switch as an AVX2-only split.

Critical Checkpoints

• Goal of current task: Improve BE performance when USE_AVX2=ON. The flag may help on x86-64-v3 CPUs, but the PR does not fully accomplish the task safely because it silently raises the minimum ISA beyond AVX2 without updating the surrounding compatibility contract. No test was added to prove the new baseline is safe.
• Modification size and focus: The code diff is tiny, but the behavioral impact is broad: every AVX2-enabled x86_64 BE build now targets x86-64-v3. The surrounding contract changes are missing.
• Concurrency: Not applicable; this is a build-system change only.
• Lifecycle / static initialization: Applicable indirectly. BE relies on an early startup instruction probe in be/src/service/doris_main.cpp, but that probe no longer matches the compiler target after this change.
• Configuration items: No new config was added, but the meaning of existing USE_AVX2 effectively changes from "enable AVX2" to "require x86-64-v3". Existing docs, package naming, and runtime guidance are therefore stale.
• Incompatible changes: Yes. This raises the minimum CPU feature set for the default AVX2-enabled BE binary. Compatibility handling is incomplete.
• Parallel code paths: Related paths (build.sh, build-for-release.sh, and the BE startup instruction check) were not updated consistently with the new ISA baseline.
• Special conditional checks: The if (USE_AVX2) condition is no longer precise enough for what is being enabled.
• Test coverage: No build or runtime validation was added for CPUs/toolchains around the new boundary, and there is no regression coverage for the changed packaging/runtime contract.
• Test results modified: No.
• Observability: Existing startup error reporting is insufficient for the newly required feature set.
• Transaction / persistence: Not applicable.
• Data writes / modifications: Not applicable.
• FE-BE variable passing: Not applicable.
• Performance: The potential upside on x86-64-v3 CPUs is clear, but it comes with an unhandled compatibility regression.
• Other issues: No additional blockers beyond the compatibility-contract mismatch below.

[zclllyybb]

run buildall

[zclllyybb]

run beut

it's OK

[zclllyybb]

run buildall

[hello-stephen]

BE Regression && UT Coverage Report

Increment line coverage 100% (0/0) 🎉

Increment coverage report
Complete coverage report

Category	Coverage
Function Coverage	71.94% (26851/37324)
Line Coverage	55.06% (285421/518395)
Region Coverage	51.99% (235785/453513)
Branch Coverage	53.41% (101839/190687)

[zclllyybb]

skip buildall