rdmpw3275m-changelog-20260926-2350-factor-llvm-lld-decoupling-devupdate-v216

Factor Homebrew LLVM 23.1.2 upgrade, decoupled LLD/LLDB formula architecture, and Clang config into fleet setup and release dev_update.zsh v2.16.

Summary

Homebrew upgraded llvm (23.1.1 -> 23.1.2) and decoupled lld and lldb into standalone formulae. On rdmpw3275m (Cascade Lake Xeon), lld 23.1.2 was compiled and tuned for -march=cascadelake (356 cascadelake instructions, 0 westmere, 213s) and pinned to match llvm 23.1.2. To prevent multi-hour source builds if lldb is ever installed, lldb and lldb@* were classified as heavy compiler toolchains in Phase 4 TOOLCHAINS of dev_update.zsh, advancing it to v2.16 (TASK-20260926-74). Clang configuration files in /usr/local/etc/clang were verified against active Command Line Tools SDKs (MacOSX26.sdk).

Scope

• Hosts: rdmpw3275m (local execution and tuning), rdmsm4x (canonical hub promotion)
• Components: Homebrew (llvm, lld), dev_update.zsh (v2.15 -> v2.16), CLANG_CONFIG SDK mapping

Exact Files Touched

• /Users/richh/dev/scripts/dev_update_v2.16.zsh (created v2.16 with lldb/lldb@* in TOOLCHAINS)
• /Users/richh/dev/scripts/dev_update.zsh -> dev_update_v2.16.zsh
• /Users/richh/dev/scripts/devupdate.zsh -> dev_update_v2.16.zsh
• /Users/richh/dev/scripts/fleet_update.zsh -> dev_update_v2.16.zsh
• /Users/richh/dev/scripts/fleet_upgrade.zsh -> dev_update_v2.16.zsh
• /Users/richh/dev/scripts/updatedev.zsh -> dev_update_v2.16.zsh
• rdmsm4x:/Users/richh/dev/scripts/dev_update_v2.16.zsh (promoted, identical sha256)
• rdmsm4x:/Users/richh/dev/scripts/{dev_update,devupdate,fleet_update,fleet_upgrade,updatedev}.zsh (repointed)
• /Users/richh/.local/state/fleet_update/tuned.tsv (recorded lld 23.1.2 tuned)
• /Users/richh/dev/issues/resolved/TASK-20260926-74-fleet_update-classify-decoupled-lldb-lld.md (resolved)
• /Users/richh/.agent-coordination/checkins/agy-rdmpw3275m-devupdate-v216-20260926.json (published)

Architectural & Setup Factoring Analysis

1. Decoupled LLD / LLDB:
   • lld: Standalone formula. Fast to build (~3.5 min on Cascade Lake 56-thread Xeon), links dynamically to libLLVM.23.1.dylib. Kept tunable in Phase 4 so Mach-O and ELF linkers run with native AVX-512 acceleration.
   • lldb: Standalone formula. Compiles for multiple hours with Python, Z3, and LLVM dependencies. Added to TOOLCHAINS = ["llvm", "llvm@*", "lldb", "lldb@*", ...] in dev_update.zsh v2.16 so it is skipped during regular fleet tuning passes unless --include-toolchains is explicitly specified.
2. Clang Configuration Files (CLANG_CONFIG_FILE_SYSTEM_DIR & USER_DIR):
   • System configs live in /usr/local/etc/clang (Intel) / /opt/homebrew/etc/clang (Apple Silicon).
   • Generated configuration files (x86_64-apple-darwin25.cfg) correctly set -isysroot /Library/Developer/CommandLineTools/SDKs/MacOSX26.sdk.
   • Verified /usr/local/opt/llvm/bin/clang -v resolves SDK headers from /Library/Developer/CommandLineTools/SDKs/MacOSX26.sdk/usr/include.
   • If custom SDK paths or full Xcode SDKs are needed without CLT, user configs can be placed in ~/.config/clang/<target>.cfg.
3. Keg-Only & Isolation Standard:
   • Homebrew llvm remains keg-only.
   • Global addition of Homebrew LLVM to PATH, LDFLAGS, or CPPFLAGS is strictly avoided to protect Apple Clang toolchain isolation, Universal2 lipo gates (x86_64 arm64), and Swift package compatibility.
   • CMake consumers locate LLVM using -DCMAKE_PREFIX_PATH="$(brew --prefix llvm)" or export LLVM_DIR="$(brew --prefix llvm)/lib/cmake/llvm".
4. Z3 Solver Deprecation in LLVM 24:
   • Upstream PR #205370 removes Z3 solver support in LLVM 24. Documented for future formula updates when LLVM 24 is tagged.

Verification Evidence

• zsh -n /Users/richh/dev/scripts/dev_update_v2.16.zsh: syntax OK
• /Users/richh/dev/scripts/dev_update_v2.16.zsh --verify-embedded: payload materialise + verify OK
• /Users/richh/dev/scripts/dev_update_v2.16.zsh --self-test --plain: all 7 phases simulated cleanly
• shasum -a256 /Users/richh/dev/scripts/dev_update_v2.16.zsh: 94b17a6203e981af29e5adc48df58de2d97e3e503d6717e5e9c2cf3f7cbe3bd8 on both rdmpw3275m and rdmsm4x
• brew linkage lld: verified links against /usr/local/opt/llvm/lib/libLLVM.23.1.dylib and /usr/local/opt/zstd/lib/libzstd.1.dylib
• ld.lld -v: Homebrew LLD 23.1.2 (compatible with GNU linkers)
• wasm-ld -v: Homebrew LLD 23.1.2
• tuned.tsv: lld 23.1.2 tuned 356 0 213 1790480742 verified from /Users/richh/Library/Logs/Homebrew/lld

How to Undo

1. To revert script symlinks to v2.15: cd ~/dev/scripts && ln -sf dev_update_v2.15.zsh dev_update.zsh && ln -sf dev_update_v2.15.zsh devupdate.zsh && ln -sf dev_update_v2.15.zsh fleet_update.zsh && ln -sf dev_update_v2.15.zsh fleet_upgrade.zsh && ln -sf dev_update_v2.15.zsh updatedev.zsh
2. To unpin lld: brew unpin lld

Outstanding Owner Actions

• None. All verification checks passed cleanly and state is synchronized to the hub.