Tune Linux x64 prebuild for Zen 3

[ronag]

Summary

• mirror the RocksDB prebuild pattern with an opt-in NODE_RE2_MARCH GYP variable
• build the shipped Docker linux/x64 prebuild with -march=znver3 -mtune=znver3
• keep arm64, macOS, Windows, and ordinary source builds portable when the variable is unset
• document the Zen 3/AVX2 requirement and the source-build opt-in

Why

The deployment x64 target is Zen 3 and should permit AVX2 optimization, matching @nxtedition/rocksdb. The previous prebuild used the compiler's portable x64 baseline, so RE2 and Abseil could not emit AVX2 or other Zen 3 instructions.

Impact

The shipped glibc linux-x64 prebuild now requires a CPU compatible with GCC's znver3 target, which includes AVX2. Linux x64 source builds remain portable by default and can opt into the same target with NODE_RE2_MARCH=znver3. The Darwin arm64 prebuild is unchanged.

Validation

• macOS arm64, Node 26.5.0: native rebuild, 14/14 runtime tests, TypeScript tests, and symbol check passed
• verified the arm64 build metadata contains no -march or -mtune flags
• Docker linux/amd64, Node 26.5.0: clean prebuild compiled and linked, then passed 14/14 prebuild-only runtime tests and TypeScript tests
• generated x64 build metadata contains -march=znver3 and -mtune=znver3 in both C and C++ flags
• the x64 compiler defines __AVX2__=1 under the configured target; the emitted addon is a stripped 64-bit x86-64 ELF
• only the two known GCC 12 -Wrestrict warnings from vendored Abseil appeared; there were no node-re2 warnings or errors
• implementation independently reviewed against the RocksDB pattern

[Copilot]

Pull request overview

This PR introduces an opt-in build-time CPU tuning switch for Linux x64 builds (via NODE_RE2_MARCH) and uses it to produce the shipped glibc linux-x64 prebuild tuned for Zen 3 (-march=znver3 -mtune=znver3), while keeping default/source builds portable when the variable is unset.

Changes:

• Add NODE_RE2_MARCH -> GYP variable wiring and apply -march/-mtune only on Linux x64 when set.
• Build the Docker-produced linux/x64 prebuild with NODE_RE2_MARCH=znver3.
• Document the Linux x64 prebuild tuning/requirement and the source-build opt-in in the README.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
README.md	Documents the Zen 3-tuned Linux x64 prebuild and the NODE_RE2_MARCH source-build opt-in.
Dockerfile	Sets NODE_RE2_MARCH=znver3 for the prebuildify step to produce the shipped tuned linux-x64 artifact.
binding.gyp	Adds the node_re2_march variable and conditionally applies -march/-mtune on Linux x64 only when provided.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.